WO2013183692A1 - Flexible printed wiring board and method for producing flexible printed wiring board - Google Patents

Flexible printed wiring board and method for producing flexible printed wiring board Download PDF

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Publication number
WO2013183692A1
WO2013183692A1 PCT/JP2013/065644 JP2013065644W WO2013183692A1 WO 2013183692 A1 WO2013183692 A1 WO 2013183692A1 JP 2013065644 W JP2013065644 W JP 2013065644W WO 2013183692 A1 WO2013183692 A1 WO 2013183692A1
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WO
WIPO (PCT)
Prior art keywords
conductor
wiring board
printed wiring
flexible printed
conductive
Prior art date
Application number
PCT/JP2013/065644
Other languages
French (fr)
Japanese (ja)
Inventor
岡　良雄
春日　隆
直太 上西
Original Assignee
住友電気工業株式会社
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by 住友電気工業株式会社 filed Critical 住友電気工業株式会社
Priority to CN201380023779.2A priority Critical patent/CN104272882B/en
Publication of WO2013183692A1 publication Critical patent/WO2013183692A1/en

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    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K1/00—Printed circuits
    • H05K1/02—Details
    • H05K1/11—Printed elements for providing electric connections to or between printed circuits
    • H05K1/115—Via connections; Lands around holes or via connections
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K3/00—Apparatus or processes for manufacturing printed circuits
    • H05K3/40—Forming printed elements for providing electric connections to or between printed circuits
    • H05K3/4038—Through-connections; Vertical interconnect access [VIA] connections
    • H05K3/4053—Through-connections; Vertical interconnect access [VIA] connections by thick-film techniques
    • H05K3/4069—Through-connections; Vertical interconnect access [VIA] connections by thick-film techniques for via connections in organic insulating substrates
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K1/00—Printed circuits
    • H05K1/02—Details
    • H05K1/11—Printed elements for providing electric connections to or between printed circuits
    • H05K1/118—Printed elements for providing electric connections to or between printed circuits specially for flexible printed circuits, e.g. using folded portions
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K2201/00—Indexing scheme relating to printed circuits covered by H05K1/00
    • H05K2201/03—Conductive materials
    • H05K2201/0332—Structure of the conductor
    • H05K2201/0388—Other aspects of conductors
    • H05K2201/0394—Conductor crossing over a hole in the substrate or a gap between two separate substrate parts

Definitions

  • the present invention relates to a flexible printed wiring board provided with a blind via formed of a conductive paste, and a method for manufacturing the flexible printed wiring board.
  • Patent Document 1 discloses an example of a printed wiring board in which blind vias are formed using a conductive paste.
  • the blind via 100 includes a first land portion 111 formed on the first surface of the substrate 110, a second land portion 112 formed on the second surface of the substrate 110, and a first land. And a conductor 114 that connects the portion 111 and the second land portion 112.
  • the conductor 114 is formed by filling the via hole 113 with a conductive paste and curing the conductive paste.
  • the surface 115 of the conductor 114 is processed flat.
  • the flexible printed wiring board is disclosed also in patent document 2, the shape of the conductor 210 is different from the flexible printed wiring board of FIG. As shown in FIG. 9, a depression 212 is provided on the surface 211 of the conductor 210 of the blind via 200.
  • ⁇ Flexible printed circuit boards are placed in a bent state or bent repeatedly.
  • a force is applied to the blind via. Therefore, when the stress applied to the conductive layer and the conductor becomes larger than the adhesive force between the conductive layer and the conductor, the conductor peels from the conductive layer. Peeling between the conductive layer and the conductor increases the contact resistance of the blind via and reduces the reliability of the electric circuit using the flexible printed wiring board. For this reason, it is required that the contact resistance between the conductor and the conductive layer does not increase due to bending of the flexible printed wiring board.
  • the present invention has been made to solve such problems, and an object of the present invention is to provide a flexible printed wiring board capable of suppressing an increase in the contact resistance of a blind via against bending, and the flexible printed wiring board. It is in providing the manufacturing method of.
  • the base material the first conductive layer formed on the first surface of the base material, and the second conductive layer formed on the second surface of the base material.
  • a flexible printed wiring board provided with the conductor which connects a said 1st conductive layer and a said 2nd conductive layer is provided.
  • the flexible printed wiring board includes a first land portion provided on the first conductive layer and a second land portion provided on the opposite side of the first land portion with the base material sandwiched between the second conductive layers. And a via hole penetrating the first land portion and the base material and reaching the second land portion.
  • the conductor is formed of a conductive paste, and the conductor fills the via hole so as to cover the entire bottom surface of the via hole, and at least a part of the surface of the first land portion. And the thickness of the conductor on the central axis of the via hole is smaller than the sum of the thickness of the base material and the thickness of the first land portion.
  • the outer surface of the substrate extends and the inner surface contracts. At this time, force is applied in a direction in which the first land portion and the conductor are separated from each other. As a result, a gap is generated between the conductor and the first land portion, and the contact resistance of the blind via is increased.
  • the degree of increase in the contact resistance of the blind via depends on the structure of the conductor constituting the blind via.
  • the thickness of the conductor on the central axis of the via hole is made smaller than the sum of the thickness of the base material and the thickness of the first land portion.
  • a recess is provided on the central axis of the via hole so that the conductor is easily deformed, and the conductor is easily deformed following the deformation of the base material.
  • the thickness of the conductor on the central axis of the via hole is preferably 5 ⁇ m or more.
  • the conductor is deformed when the flexible printed wiring board is bent.
  • the conductor is thin, there is a high possibility that the conductor will crack. Therefore, if the thickness of the conductor is 5 ⁇ m or more, it is possible to suppress the occurrence of cracks in the conductor as compared with the case where the thickness of the conductor on the central axis of the via hole is less than 5 ⁇ m.
  • the thickness of the thickest portion of the conductor covering the first land portion is 2 ⁇ m or more.
  • the contact resistance between the conductor and the first land portion increases. Considering this point, if the thickness of the thickest portion covering the first land portion is 2 ⁇ m or more, the occurrence of cracks in the portion covering the first land portion can be suppressed.
  • an inner circle and an outer circle of the cross section In a cross section of the conductor when the conductor is cut by a plane perpendicular to the central axis of the via hole and including the surface of the first land portion, an inner circle and an outer circle of the cross section The distance between is preferably 5 ⁇ m or more.
  • the portion of the conductor corresponding to the opening of the via hole is likely to crack. Considering this point, if the distance between the inner circle and the outer circle of the cross section of the conductor is set to 5 ⁇ m or more, a crack occurs in a portion corresponding to the opening on the first land side of the via hole. This can be suppressed.
  • the conductor preferably includes flat spherical conductive particles and a combination thereof.
  • the gaps between the conductive particles increase.
  • the conductive particles are flat spherical, the gap between the conductive particles is small.
  • the base material the first conductive layer formed on the first surface of the base material, and the second conductive layer formed on the second surface of the base material.
  • a method of manufacturing a flexible printed wiring board comprising a conductor connecting the first conductive layer and the second conductive layer.
  • the method includes forming the conductor using a conductive paste having a thixotropy index of 0.25 or less represented by the following formula (1).
  • Thixotropic index log ( ⁇ 1 / ⁇ 2) / log (D2 / D1) (1)
  • ⁇ 1 indicates the viscosity of the conductive paste when the shear rate D1 is 2 s ⁇ 1
  • ⁇ 2 indicates the viscosity of the conductive paste when the shear rate D2 is 20 s ⁇ 1 .
  • the upper part of the conductor is raised by the surface tension.
  • the electrically conductive paste of this invention the center part of the upper part of a conductor can be depressed. This is due to the following reason.
  • the conductive paste has a property that the viscosity increases as it approaches a state where no shear stress is applied, that is, thixotropic property.
  • the thixotropy index indicates that the smaller the value, the lower the thixotropy. That is, after applying a conductive paste having a thixotropy index of 0.25 or less to a substrate, the conductive paste can be flowed, so that a depression can be formed in the upper central portion of the conductor.
  • the conductor may be formed using a conductive paste containing flat spherical conductive particles and having a mass ratio of the flat spherical conductive particles of 70% by mass or more. desirable.
  • the upper central portion of the conductor can be recessed.
  • the conductive paste further includes spherical conductive particles having an average particle size of 30 nm to 200 nm.
  • the upper central portion of the conductor can be recessed.
  • the conductive paste includes, as the flat spherical conductive particles, first conductive particles having an average particle size of 1.4 ⁇ m or more and 3.3 ⁇ m or less, and first conductive particles having an average particle size of 0.5 ⁇ m or more and 1.8 ⁇ m or less. 2 conductive particles are desirably included. In this case, the upper central portion of the conductor can be recessed.
  • conductive particles having an average particle size of 1.4 ⁇ m or more and 3.3 ⁇ m or less are included in the conductive paste, the following effects can be obtained. That is, conductive particles having a size of 1.4 ⁇ m or more and 3.3 ⁇ m or less increase the thickness of the conductive paste. Thereby, it can suppress that the film thickness of an electrically conductive paste becomes small too much. If conductive particles having an average particle size larger than 3.3 ⁇ m are included in the conductive paste, the film thickness becomes too thick.
  • the present invention it is possible to provide a flexible printed wiring board capable of suppressing an increase in the contact resistance of the blind via against bending and a method for manufacturing the flexible printed wiring board.
  • the flexible printed wiring board 1 includes a base material 30, a first conductive pattern 10 (first conductive layer) formed on the first surface 31 of the base material 30, and a second surface 32 of the base material 30.
  • 2 conductive pattern 20 (2nd conductive layer), and the conductor 40 which connects the 1st conductive pattern 10 and the 2nd conductive pattern 20 are provided.
  • the second surface 32 of the substrate 30 is located on the side opposite to the first surface 31.
  • the base material 30 is formed of a flexible insulating film.
  • the base material 30 is made of polyimide, polyethylene terephthalate, or the like.
  • the thickness of the base material 30 is appropriately selected according to the use of the flexible printed wiring board 1. Specifically, a substrate 30 having a thickness of 5 ⁇ m to 50 ⁇ m is employed.
  • Each conductive pattern 10 and 20 is formed by processing the metal layer of the base material 30.
  • the conductive patterns 10 and 20 are formed by etching a double-sided copper-clad laminate.
  • it may replace with a double-sided copper clad laminated board, and may use the board
  • the thickness of the first conductive pattern 10 is appropriately selected according to the use of the flexible printed wiring board 1.
  • the second conductive pattern 20 is formed in the same manner as the first conductive pattern 10.
  • the blind via 50 that connects the first conductive pattern 10 and the second conductive pattern 20 will be described.
  • the blind via 50 includes a first land portion 11, a second land portion 21, and a conductor 40 that connects the land portions 11 and 21.
  • the first land portion 11 is circular, and a land hole 11b is formed at the center thereof.
  • the diameter of the first land portion 11 is set to 300 ⁇ m to 1000 ⁇ m, for example.
  • the first land portion 11 is a part of the first conductive pattern 10.
  • the second land portion 21 is provided on the opposite side of the first land portion 11 with the base material 30 interposed therebetween.
  • the second land portion 21 is formed in a circular shape.
  • the diameter of the second land portion 21 is set to 100 ⁇ m to 1000 ⁇ m.
  • the second land portion 21 is a part of the second conductive pattern 20.
  • the shape of the 1st land part 11 and the 2nd land part 21 should not be limited to circular, A rectangle may be sufficient.
  • the first land portion 11 and the base material 30 are formed with via holes 33 penetrating the first land portion 11 and the base material 30 up to the second land portion 21.
  • the bottom surface 33 b of the via hole 33 corresponds to the inner surface of the second land portion 21.
  • the bottom surface 33b of the via hole 33 is substantially circular.
  • the via hole 33 is formed by, for example, laser irradiation.
  • the diameter of the via hole 33 is, for example, 20 ⁇ m to 300 ⁇ m.
  • the land hole 11 b constitutes a part of the via hole 33.
  • the conductor 40 fills the via hole 33 so as to cover the entire bottom surface 33 b of the via hole 33.
  • the conductor 40 covers part or all of the surface 11 a of the first land portion 11.
  • the bottom portion 42 of the conductor 40 is in contact with the second land portion 21.
  • the upper portion 41 of the conductor 40 is in contact with the first land portion 11.
  • a depression 44 exists in the central portion of the upper portion 41 of the conductor 40.
  • the bottom portion 42 of the conductor 40 is in contact with the second conductive pattern 20 in the central axis direction Da of the via hole 33.
  • the upper portion 41 of the conductor 40 includes a portion that contacts the first conductive pattern 10 in the central axis direction Da of the via hole 33 and partially covers the first land portion 11.
  • the thickness td of the conductor 40 on the central axis Ca of the via hole 33 is smaller than the sum of the thickness ta of the base material 30 and the thickness tb of the first land portion 11. Further, the thickness td of the conductor 40 on the central axis Ca of the via hole 33 is set to 5 ⁇ m or more.
  • the thickness te of the thickest portion of the conductor 40 that covers the first land portion 11 is 2 ⁇ m or more.
  • an inner circle and an outer portion of the cross section of the conductor 40 are cut.
  • the distance Df between the circle (via hole 33) is 5 ⁇ m or more.
  • the conductor 40 is formed of a conductive paste containing conductive particles 60 and a binder resin. That is, the conductor 40 is a structure including the conductive particles 60 and a combined body that couples the conductive particles 60.
  • the conductive particles 60 are melt bonded or sintered bonded at the contact portion. There is also a portion where the conductive particles 60 are simply in contact with each other.
  • the conductive particles 60 are fixed to each other with a binder resin. Since the binder resin shrinks during heat curing, the conductive particles 60 are present in a state where they are pressed against each other.
  • the binder resin is a thermosetting resin and exists as a cured product in the conductor 40.
  • Part or all of the conductive particles 60 included in the conductive paste are metal particles having a flattened sphere shape (hereinafter referred to as “flattened spherical shape”), and in the conductor 40, they exist as a bonded body. .
  • the metal particles are made of silver, copper, nickel or the like.
  • FIG. 3A shows a perspective view of the conductive particles 60.
  • FIG. 3B is a plan view of the conductive particles 60 viewed from a direction along the rotational symmetry axis Cr (hereinafter, rotational symmetry axis direction Dr).
  • FIG. 3C shows a cross-sectional view of the conductive particles 60.
  • the shape of the conductive particles 60 viewed from the rotationally symmetric axis direction Dr is substantially circular (a shape approximated to a circle).
  • the cross section when the conductive particles 60 are cut along the plane including the rotational symmetry axis Cr is a shape obtained by crushing a circle.
  • the ratio of the short side Lx to the long side Ly (short side Lx / long side Ly) of the cross section is 0.2 or more and less than 1.0.
  • Such flat spherical conductive particles 60 are formed by crushing spherical metal particles with a pressing machine or the like.
  • the blind via 350 having a conventional structure is one having no depression 44 on the central axis Cb of the via hole 333.
  • a shear stress Fx is generated along the boundary surface between the surface 311a of the first land portion 311 and the conductor 340.
  • a vertical stress Fy is generated in a direction perpendicular to the boundary surface between the inner peripheral surface 333a of the via hole 333 and the conductor 340.
  • a tensile stress Fz is generated in the upper part 341 of the conductor 340.
  • the upper part 341 of the conductor 340 is deformed following the base material 330. That is, when the bending of the flexible printed wiring board 300 is small, the shear stress Fx is smaller than the adhesive force between the surface 311 a of the first land portion 311 and the conductor 340, or the vertical stress Fy is the via hole 333. Since it is smaller than the adhesive force between the inner peripheral surface 333a and the conductor 340, the conductor 340 does not peel from the first land portion 311.
  • the upper portion 341 of the conductor 340 is peeled from the first land portion 311. That is, when the bending of the flexible printed wiring board 300 is large, the upper portion 341 of the conductor 340 is greatly bent, the strain ⁇ increases, and the tensile stress Fz applied to the upper portion 341 of the conductor 340 increases. As a result, the shear stress Fx becomes larger than the adhesive force between the surface 311a of the first land portion 311 and the conductor 340, and the vertical stress Fy is between the inner peripheral surface 333a of the via hole 333 and the conductor 340. Since it becomes larger than the adhesive force, the upper portion 341 of the conductor 340 is peeled from the first land portion 311 as shown in FIG.
  • Such peeling occurs when the bending of the flexible printed wiring board 300 is smaller than a predetermined curvature but the bending frequency is high.
  • the bending frequency is high, since the shear stress Fx is repeatedly applied to the bonding portion between the surface 311a of the first land portion 311 and the conductor 340, the bonding force of the bonding portion gradually decreases and peeling occurs.
  • the strain ⁇ of the upper portion 41 of the conductor 40 when the flexible printed wiring board 1 is bent is small. That is, the upper portion 41 of the conductor 40 is recessed unlike the blind via 350 having a conventional structure. Such a depression 44 shortens the length Ls from the second land portion 21 to the surface 43 of the conductor 40 as compared with the blind via 350 having a conventional structure. Since the magnitude of the strain ⁇ of the surface portion of the conductor 40 is smaller as it is closer to the second land portion 21, the strain ⁇ of the upper portion 41 of the conductor 40 is reduced by the presence of such a depression 44.
  • the shear stress Fx becomes larger than the adhesive force between the surface 11a of the first land portion 11 and the conductor 40, or the vertical stress Fy. Is prevented from becoming larger than the adhesive force between the inner peripheral surface 33a of the via hole 33 and the conductor 40. For this reason, as shown in FIG. 5, the upper portion 41 of the conductor 40 does not peel from the first land portion 11, and the upper portion 41 of the conductor 40 is deformed following the base material 30. Next, a method for manufacturing the flexible printed wiring board 1 will be described.
  • the conductive patterns 10 and 20 are formed on both surfaces of the base material 30 by an etching method.
  • the first conductive pattern 10 includes a land portion.
  • the second conductive pattern 20 includes a second land portion 21.
  • the land portion of the first conductive pattern 10 is changed to the first land portion 11 by forming a land hole 11b by a laser in the next step.
  • the via hole 33 is formed by a laser. Specifically, by irradiating the land portion of the first conductive pattern 10 with a laser, a hole (via hole 33) penetrating both the land portion and the substrate 30 is formed.
  • the via paste 33 is filled with the conductive paste by a printing method. After filling, the conductive paste is allowed to flow until the conductive paste is in a stable and static state. That is, the conductive paste is caused to flow until the central portion of the via hole 33 is depressed. Specifically, the base material 30 after filling with the conductive paste is left at room temperature for several minutes to several hours. Thereafter, the substrate 30 is heated to cure the conductive paste. Conductive paste Next, the conductive paste will be described.
  • the conductive paste has a property that after filling the via hole 33, it flows for a period of time and does not spread too much along the via hole 33.
  • the conductive paste contains conductive particles, a binder resin, and a solvent.
  • the conductive particles the flat spherical metal particles (corresponding to the second conductive particles in Table 1) shown in FIG. 3 are used.
  • the mass ratio of the silver particles to the entire conductive paste (hereinafter also simply referred to as mass ratio) is preferably 70% by mass or more.
  • the average particle size indicates a particle size corresponding to a value of 50% in terms of a volume cumulative value in a volume cumulative distribution of the particle size of the conductive particles 60 (diameter of the conductive particles 60 in plan view).
  • the conductive paste preferably contains two or more kinds of conductive particles having different average particle diameters as flat spherical conductive particles.
  • conductive particles having an average particle size of 0.5 ⁇ m to 1.8 ⁇ m hereinafter referred to as second conductive particles
  • conductive particles having an average particle size of 1.4 ⁇ m to 3.3 ⁇ m hereinafter referred to as first particles. (Referred to as conductive particles) in the conductive paste.
  • spherical conductive particles (hereinafter referred to as third conductive particles) be present in addition to the flat spherical conductive particles 60 in the conductive paste.
  • the spherical conductive particles preferably have an average particle size smaller than the average particle size of the flat spherical conductive particles 60.
  • spherical conductive particles having an average particle size of 30 nm to 200 nm are used.
  • the mass ratio of the spherical conductive particles is set smaller than the mass ratio of the flat spherical conductive particles 60.
  • the mass ratio of the spherical conductive particles is set to 1.0% by mass or more and 15% by mass or less.
  • conductive particles having an average particle size of 1.4 ⁇ m or more and 3.3 ⁇ m or less
  • coating particles whose surfaces are coated with metal can be used.
  • silver-coated copper particles in which copper particles are coated with silver can be used.
  • epoxy resin epoxy resin, phenol resin, polyester resin, acrylic resin, melamine resin, polyimide resin, polyamideimide resin, phenoxy resin, or the like is used.
  • a thermosetting resin is employed. Epoxy resins are particularly suitable.
  • the type of epoxy resin is not particularly limited.
  • a bisphenol type epoxy resin made from bisphenol A, bisphenol F, bisphenol S, bisphenol AD or the like is used.
  • a naphthalene type epoxy resin, a novolac type epoxy resin, a biphenyl type epoxy resin, a dicyclopentadiene type epoxy resin, or the like can also be used.
  • Epoxy resins include one-component and two-component epoxy resins, and any of them can be used.
  • a one-component epoxy resin in which a microcapsule type curing agent is dispersed in a main agent (epoxy resin).
  • a microcapsule type curing agent for example, butyl carbitol acetate or ethyl carbitol acetate is used as a solvent.
  • the mass ratio of the various conductive particles, the binder resin, and the solvent is set so as to satisfy the following expression (1).
  • Thixotropic index ⁇ 0.25
  • Thixotropic index log ( ⁇ 1 / ⁇ 2) / log (D2 / D1)
  • ⁇ 1 indicates the viscosity (Pa ⁇ s) of the conductive paste when the shear rate D1 is 2 s ⁇ 1
  • ⁇ 2 indicates the viscosity (Pa ⁇ s) of the conductive paste when the shear rate D2 is 20 s ⁇ 1 .
  • the average particle diameter and mass ratio of the conductive particles 60, the type and number of types of the conductive particles 60 included in the conductive paste, the type and mass ratio of the binder resin, the type and mass ratio of the solvent so that the formula (1) is satisfied. Etc. are set.
  • the type of the conductive particles 60 indicates a classification according to shape, such as spherical conductive particles and flat spherical conductive particles.
  • the number of types indicates the number of types of conductive particles included in the conductive paste.
  • Such a conductive paste has the following properties.
  • the conductive paste flows for a while.
  • a recess 44 is formed on the central axis Ca of the via hole 33.
  • Such properties can be realized by selecting the shape of the conductive particles 60. Hereinafter, this point will be described.
  • the fluidity of the conductive paste can be adjusted by the binder resin.
  • the mass ratio of the binder resin to the entire conductive paste is small, the fluidity adjustment range is small. For this reason, it is difficult to adjust the thixotropy index by selecting the type of binder resin.
  • the fluidity of the conductive paste is small because the scaly conductive particles 60 are present in a state of being caught with each other.
  • the spherical conductive particles 60 are the main component of the conductive paste, since the spherical conductive particles 60 are not caught, the fluidity of the conductive paste increases and may spread beyond the first land portion 11. .
  • flat spherical conductive particles 60 having an average particle size of 0.5 ⁇ m or more and 3.3 ⁇ m or less are used as the main component of the conductive paste.
  • the conductive particles 60 having such a shape the fluidity and shape retention shown above are exhibited. This is because the flat spherical conductive particles 60 are easy to flow because the mutual catching is small, and the flat spherical conductive particles 60 are rearranged into a dense and structurally stable state with this flow. It is thought that it is caused by being done.
  • Table 1 gives examples of conductive paste.
  • the conductive pastes 1 to 4 are suitable for manufacturing the flexible printed wiring board 1 of the present embodiment.
  • the conductive pastes 1 to 3 are particularly preferable for use in manufacturing the flexible printed wiring board 1 of the present embodiment.
  • the conductive paste 5 is an example of a conductive paste to be compared.
  • the first conductive particles are silver-coated copper particles and have a flat spherical shape as shown in FIG.
  • the average particle diameter (diameter in plan view) of the first conductive particles is 1.9 ⁇ m.
  • the second conductive particles are silver particles and have a flat spherical shape as shown in FIG.
  • the average particle size of the second conductive particles is 0.9 ⁇ m.
  • the third conductive particles are spherical silver particles.
  • the average particle diameter of the third conductive particles is 100 nm.
  • the epoxy resin is a bisphenol A type epoxy resin having a molecular weight of 45000 to 55000.
  • the curing agent indicates a microencapsulated imidazole-based latent curing agent (manufactured by Asahi Kasei E-Materials Co., Ltd., NovaCure (registered trademark) HX3941HP).
  • the viscosity of each conductive paste was measured using a viscometer (manufactured by Toki Sangyo Co., Ltd., TVE-22HT) at a temperature of 25 ° C. ⁇ 0.2 ° C. and a cone rotor (manufactured by Toki Sangyo Co., Ltd., 3 ° ⁇ R7.7 ( Measurement was performed using a rotor cord 07)).
  • the conductive pastes 1 to 3 satisfy the above formula (1) (thixotropic index is 0.25 or less). This is because the mass ratio of the flat spherical conductive particles (first conductive particles and second conductive particles) is set to 70% by mass or more, and the mass ratio of the first conductive particles is smaller than the mass ratio of the second conductive particles. This is because the conductive paste was prepared.
  • the conductive pastes 4 and 5 do not satisfy the above formula (1) (thixotropic index is 0.25 or less). This is because the mass ratio of the flat spherical first conductive particles is excessively increased.
  • the first conductive particles are flat spherical conductive particles having an average particle diameter of 1.9 ⁇ m
  • the second conductive particles are flat spherical conductive particles having an average particle diameter of 0.9 ⁇ m.
  • a conductive paste satisfying the equation is realized.
  • the mass ratio of the conductive particles is set to 70% by mass or more and the mass of the first conductive particles is set.
  • the conductive paste 4 is slightly deviated from the range defined in the above formula (1).
  • this conductive paste 4 as shown in Example 4 below, the depression 44 of the present embodiment A blind via 50 can be formed. However, the depth of the recess 44 of the blind via 50 is small.
  • Example An example of the flexible printed wiring board 1 will be described.
  • the flexible printed wiring board 1 of each embodiment has the same structure except for the structure of the blind via 50.
  • FIGS. 6A and 6B show the flexible printed wiring board 1 according to each embodiment.
  • FIG. 6A is a plan view of the flexible printed wiring board 1
  • FIG. 6B is a cross-sectional view of the flexible printed wiring board 1.
  • FIG. The flexible printed wiring board 1 has 36 blind vias 50 connected in a daisy chain shape.
  • Each first land portion 11 is formed on the first surface 31 of the base material 30.
  • Each second land portion 21 is formed on the second surface 32 of the base material 30.
  • the first land portions 11 are connected by connecting patterns 12 in order of two from the end.
  • Two second land portions 21 are connected by connecting patterns 22 in order from the end.
  • the connection pattern 12 of the second surface 32 is formed on the opposite side of the portion of the first surface 31 where there is no connection pattern 12 with the base material 30 in between. That is, in the plan view, the connection pattern 12 on the first surface 31 and the connection pattern 22 on the second surface 32 are alternately arranged.
  • each member is as follows (see FIGS. 2 and 6).
  • Dimension Dc (inner diameter of via hole 33) is 100 ⁇ m.
  • the outer diameter of the first land portion 11 is 500 ⁇ m.
  • the outer diameter of the second land portion 21 is 500 ⁇ m.
  • Dimension TD (dimension ta + dimension tb) is 24 ⁇ m.
  • “Dimension ta” in Table 2 indicates the thickness of the base material 30. “Dimension tb” indicates the thickness of the first land portion 11. “Dimension Dc” indicates the inner diameter of the via hole 33. “Dimension TD” indicates the sum of the dimension ta and the dimension tb. “Dimension td” indicates the thickness of the conductor 40 on the central axis Ca of the via hole 33. “Dimension te” indicates the thickness of the thickest portion of the conductor 40 that covers the first land portion 11 (covering portion).
  • the “dimension Df” is a cross section of the conductor 40 when the conductor 40 is cut along a plane that is perpendicular to the central axis Ca of the via hole 33 and includes the surface 11a of the first land portion 11. The distance of the smallest part in the distance between the inner circle and outer circle (via hole 33) of a cross section is shown. “Dimension Dg” indicates the distance of the portion of the conductor 40 having the smallest interval between the inner peripheral surface 33a of the via hole 33 and the outer periphery of the portion covering the first land portion 11 (covering portion). . These dimensions ta, tb, Dc, td, te, Df, and Dg indicate the average values of the 36 blind vias 50 of the flexible printed wiring board 1.
  • Example 1 the flexible printed wiring board 1 was formed using the conductive paste 1 shown in Table 1.
  • the shape of the blind via 50 is as follows (see Table 2).
  • a depression 44 was formed on the central axis Ca of the via hole 33.
  • the thickness te of the covering portion of the conductor 40 was 2 ⁇ m or more.
  • the distance Df of the conductor 40 was 5 ⁇ m or more.
  • the distance Dg of the covering portion of the conductor 40 was 5 ⁇ m or more.
  • the resistance increase rate of the blind via 50 before and after the bending test was 0.6%. This value is smaller than the determination value (10%).
  • a brass bending jig 70 having a curved surface with a radius r of 1.0 mm at the tip is prepared. Prior to the bending test, the resistance of the conductive pattern is measured. Next, a bending test is performed.
  • the first surface 31 of the flexible printed wiring board 1 according to the test is disposed outside and the flexible printed wiring board 1 is brought into close contact with the bending jig 70.
  • the flexible printed wiring board 1 is moved so as to pass through the curved surface.
  • the second surface 32 of the flexible printed wiring board 1 is set to the outside, and the flexible printed wiring board 1 is brought into close contact with the bending jig 70 so as to be curved from the first surface 71 to the second surface 72 of the bending jig 70. Move to pass.
  • Such a bending operation is counted as one time, and a total of 10 bending operations are performed.
  • the resistance change rate is obtained based on the resistance of the conductive pattern before and after the bending test.
  • the resistance change rate is obtained as an average value of the resistance change rates of the 36 blind vias 50.
  • Example 2 a flexible printed wiring board 1 having the same structure as Example 1 was formed using the conductive paste 2 shown in Table 1.
  • a depression 44 was formed on the central axis Ca of the via hole 33.
  • the thickness te (dimension te) of the covering portion of the conductor 40 was 2 ⁇ m or more.
  • the distance Df (dimension Df) of the conductor 40 was 5 ⁇ m or more.
  • the distance Dg (dimension Dg) of the covering portion of the conductor 40 was 5 ⁇ m or more.
  • the change rate of the resistance of the blind via 50 before and after the bending test was 1.4%. This value is smaller than the determination value (10%). No peeling was observed between the conductor 40 and the first land portion 11 after the bending test. That is, the same result as in Example 1 was obtained.
  • Example 3 a flexible printed wiring board 1 having the same structure as Example 1 was formed using the conductive paste 3 shown in Table 1.
  • a depression 44 was formed on the central axis Ca of the via hole 33.
  • the thickness te (dimension te) of the covering portion of the conductor 40 was 2 ⁇ m or more.
  • the distance Df (dimension Df) of the conductor 40 was 5 ⁇ m or more.
  • the distance Dg (dimension Dg) of the covering portion of the conductor 40 was 5 ⁇ m or more.
  • the change rate of the resistance of the blind via 50 before and after the bending test was 2.1%. This value is smaller than the determination value (10%). No peeling was observed between the conductor 40 and the first land portion 11 after the bending test. That is, the same result as in Example 1 was obtained.
  • Example 4 the flexible printed wiring board 1 having the same structure as that of Example 1 was formed using the conductive paste 4 shown in Table 1.
  • the recess 44 was not formed in the via hole 33 in the conductor 40.
  • the rate of change in the resistance of the blind via 50 before and after the bending test was 18.2%. This value is larger than the determination value (10%). Separation occurred between the conductor 40 and the first land portion 11 after the bending test.
  • the increment of the contact resistance of the blind via 50 with respect to the bending of the flexible printed wiring board 1 is reduced. This is mainly due to a decrease in the flexural modulus of the blind via 50 due to the presence of the recess 44.
  • Example 4 it is shown that it is more preferable to use a conductive paste having a thixotropy index of 0.25 or less in order to form the blind via 350 having such a depression 44.
  • the conductive paste having a thixotropy index of 0.28 is used to form the blind via 350 having the depression 44 and having a resistance increase rate of 10% or less after the test.
  • the depth is small. For this reason, in order to form the hollow 44 reliably, it can be said that it is preferable to make the thixotropy index
  • the mass ratio of the first conductive particles (conductive particles having an average particle size of 1.4 ⁇ m to 3.3 ⁇ m) is set to the second conductive particles (average particle size is The mass ratio of the conductive particles (0.5 ⁇ m to 1.8 ⁇ m) is preferably smaller. That is, in Example 4, the conductive paste 4 in which the mass ratio of the first conductive particles is larger than the mass ratio of the second conductive particles is used. And also with this electrically conductive paste 4, the blind via
  • the thickness (dimension td) of the conductor 40 on the central axis Ca of the via hole 33 is the same as the thickness (dimension ta) of the substrate 30 and the thickness (dimension) of the first land portion 11. It is smaller than the sum (dimension TD) with tb).
  • the degree of increase in the contact resistance of the blind via 50 depends on the structure of the conductor 40 constituting the blind via 50.
  • the conductor 40 is not deformed when the flexible printed wiring board 1 is bent, the inner peripheral surface 33a of the via hole 33 and the conductor 40 are separated from each other, or the conductor 40 is peeled from the first land portion 11. For this reason, the contact resistance of the blind via 50 increases.
  • the thickness (dimension td) of the conductor 40 on the central axis Ca of the via hole 33 is set to the thickness (dimension ta) of the substrate 30. It is smaller than the sum of the thickness (dimension tb) of the first land portion 11. That is, in the conductor 40, a recess 44 is provided on the central axis Ca of the via hole 33 so that the conductor 40 is easily deformed, and the conductor 40 is easily deformed following the deformation of the substrate 30. . Thereby, the increase in the contact resistance of the blind via 50 with respect to the bending of the flexible printed wiring board 1 can be suppressed.
  • the thickness (dimension td) of the conductor 40 on the central axis Ca of the via hole 33 is 5 ⁇ m or more.
  • the conductor 40 When the flexible printed wiring board 1 is bent, the conductor 40 is deformed. When the conductor 40 is thin, there is a high possibility that the conductor 40 will crack. In the conductor 40, if the thickness td on the central axis Ca of the via hole 33 is less than 5 ⁇ m, the possibility that the conductor 40 will crack increases. Therefore, the thickness td of the conductor 40 is set to 5 ⁇ m or more. Thereby, compared with the case where the thickness td of the conductor 40 on the central axis Ca of the via hole 33 is less than 5 ⁇ m, the occurrence of cracks in the conductor 40 can be suppressed.
  • the thickness (dimension te) of the thickest portion of the conductor 40 covering the first land portion 11 is set to 2 ⁇ m or more.
  • the portion of the conductor 40 that covers the first land portion 11 is related to the magnitude of the contact resistance between the conductor 40 and the first land portion 11.
  • the contact resistance between the conductor 40 and the first land portion 11 increases.
  • the thickness te of the thickest portion covering the first land portion 11 is set to 2 ⁇ m or more. Thereby, it can suppress that a crack generate
  • the distance Df (dimension Df) is 5 ⁇ m or more.
  • a portion of the conductor 40 corresponding to the opening 34 of the via hole 33 is likely to crack. Therefore, in the donut-shaped cross section when the conductor 40 is cut by a plane perpendicular to the central axis Ca of the via hole 33 and including the surface 11a of the first land portion 11, an inner circle of the cross section of the conductor 40 is obtained.
  • the distance Df (dimension Df) between the outer circle and the outer circle (a circle corresponding to the inner peripheral surface 33a of the via hole 33) is 5 ⁇ m or more. Thereby, it can suppress that a crack generate
  • the distance Dg (dimension Dg) is 5 ⁇ m or more.
  • the distance between the inner peripheral surface 33a of the via hole 33 and the outer periphery of the covering portion covering the first land portion 11 is the smallest distance.
  • the distance Dg (dimension Dg) is set to 5 ⁇ m or more. Thereby, it can suppress that a crack generate
  • the conductor 40 has a structure including flat spherical conductive particles 60 and a combination thereof.
  • the conductor 40 When there are protrusions on the surface of the conductive particles 60 constituting the conductor 40, the gap between the adjacent conductive particles 60 increases. Therefore, the conductor 40 is composed of flat spherical conductive particles 60, and the density of the conductive particles 60 is increased. Thereby, the allowable current amount of the blind via 50 can be increased.
  • a conductive paste having a thixotropy index of 0.25 or less is used as shown in the above formula (1).
  • the upper portion 41 of the conductor 40 rises due to surface tension.
  • the central portion of the upper portion 41 of the conductor 40 can be recessed. This is due to the following reason.
  • a conductive paste having a large thixotropy index that is, a conductive paste having an increased viscosity when no shear stress is applied, has been used. For this reason, after filling the via hole 33 with the conductive paste, the conductive paste did not spread and was in a raised state.
  • a conductive paste having a thixotropy index of 0.25 or less is used.
  • an electrically conductive paste can be made to flow.
  • the conductive paste flows along the shape of the via hole 33, and the central portion of the conductor 40 is depressed. That is, the depression 44 can be formed in the central portion of the conductor 40 by using a conductive paste having a thixotropy index of 0.25 or less.
  • a conductive paste having a thixotropy index of 0.25 or less, including flat spherical conductive particles, and a mass ratio of these flat spherical conductive particles to the entire conductive paste is 70% by mass or more is used. . Thereby, the central part of the surface 43 of the conductor 40 can be depressed.
  • the conductive paste has an average particle size of 0.5 ⁇ m or more and 1.8 ⁇ m or less and a flat spherical conductive particle (second conductive particle), and an average particle size of 1.4 ⁇ m or more and 3.3 ⁇ m or less of conductive particles (first Conductive particles). Thereby, the center part of the upper part 41 of the conductor 40 can be depressed.
  • conductive particles (first conductive particles) having an average particle size of 1.4 ⁇ m or more and 3.3 ⁇ m or less are included in the conductive paste, the following effects can be obtained. That is, the conductive particles (first conductive particles) having a size of 1.4 ⁇ m or more and 3.3 ⁇ m or less increase the thickness of the conductive paste. Thereby, it can suppress that an electrically conductive paste becomes thin too much.
  • the mass ratio of the first conductive particles is 30% by mass or less.
  • the recess 44 is difficult to be formed.
  • the depression 44 can be more reliably formed by setting the mass ratio of the first conductive particles to 30 mass% or less.
  • the spherical conductive particles (third conductive particles) having an average particle size of 30 nm to 200 nm are included in the conductive paste, and the thixotropic index of the conductive paste is set to 0.25 or less. Thereby, the center part of the upper part 41 of the conductor 40 can be depressed.
  • the means for forming the depression 44 in the conductor 40 the use of a conductive paste having a thixotropy index of 0.25 or more is adopted, but the means for forming the depression 44 is not limited to this.
  • a means of forming the depression 44 on the central axis Ca of the via hole 33 can be adopted.
  • the depth, shape, and the like of the recess 44 can be arbitrarily set by selecting a mold.
  • the structure of the conductor 40 having the depression 44 is applied to the blind via 50, but this structure is not applied only to the blind via 50.
  • the present invention can also be applied to the conductor 40. Also in this case, peeling of the conductor 40 from the hole or groove corresponding to the via hole 33 can be suppressed.
  • the present invention can also be applied to a multilayer flexible printed wiring board having three or more layers.
  • SYMBOLS 1 Flexible printed wiring board, 10 ... 1st conductive pattern, 11 ... 1st land part, 11a ... Surface, 11b ... Land hole, 12 ... Connection pattern, 20 ... 2nd conductive pattern, 21 ... 2nd land part, 22 Connection pattern, 30 ... base material, 31 ... first surface, 32 ... second surface, 33 ... via hole, 33a ... inner peripheral surface, 33b ... bottom surface, 34 ... opening, 40 ... conductor, 41 ... upper part, 42 ... bottom, 43 ... surface, 44 ... depression, 50 ... blind via, 60 ... conductive particles, 70 ... bending jig, 71 ... first surface, 72 ... second surface, 100 ...
  • blind via 110 ... base material, DESCRIPTION OF SYMBOLS 111 ... 1st land part, 112 ... 2nd land part, 113 ... Via hole, 114 ... Conductor, 115 ... Surface, 200 ... Blind via, 210 ... Conductor, 211 ... Surface, 212 ... Depression, 300 ... Flexible print wiring , 311 ... first land portion, 311a ... surface, 321 ... second land portion, 330 ... substrate, 333 ... via hole, 333a ... inner peripheral surface, 340 ... conductor, 341 ... top 350 ... blind vias.

Abstract

This flexible printed wiring board is provided with a base (30), a first conductive pattern, a second conductive pattern, and a conductor (40) that connects the first conductive pattern and the second conductive pattern with each other. The first conductive pattern has a first land portion (11), and the second conductive pattern has a second land portion (21) that is arranged opposite to the first land portion (11) across the base (30) lying therebetween. The conductor (40) is formed of a conductive paste and is arranged so that a via hole (33) that penetrates through the first land portion (11) and the base (30) and reaches the second land portion (21) is filled with the conductor (40) and at least a part of the surface of the first land portion (11) is covered with the conductor (40). The thickness of the conductor (40) above the central axis (Ca) of the via hole (33) is set to be smaller than the sum of the thickness of the base (30) and the thickness of the first land portion (11).

Description

フレキシブルプリント配線板およびフレキシブルプリント配線板の製造方法Flexible printed wiring board and method for manufacturing flexible printed wiring board
　本発明は、導電ペーストにより形成されるブラインドビアを備えるフレキシブルプリント配線板、およびそのフレキシブルプリント配線板の製造方法に関する。 The present invention relates to a flexible printed wiring board provided with a blind via formed of a conductive paste, and a method for manufacturing the flexible printed wiring board.
　基材の両面の導電層をブラインドビアで接続するフレキシブルプリント配線板において、ブラインドビアを導電ペーストで形成する技術が知られている。特許文献１には、導電ペーストによりブラインドビアを形成したプリント配線板の例が開示されている。 In a flexible printed wiring board in which conductive layers on both sides of a base material are connected by blind vias, a technique for forming blind vias with a conductive paste is known. Patent Document 1 discloses an example of a printed wiring board in which blind vias are formed using a conductive paste.
　図８に示すようにブラインドビア１００は、基材１１０の第１面に形成された第１ランド部１１１と、基材１１０の第２面に形成された第２ランド部１１２と、第１ランド部１１１と第２ランド部１１２とを接続する導電体１１４とを有する。導電体１１４は、導電ペーストをビア孔１１３に充填してこの導電ペーストを硬化することにより形成される。導電体１１４の表面１１５は平坦に加工されている。 As shown in FIG. 8, the blind via 100 includes a first land portion 111 formed on the first surface of the substrate 110, a second land portion 112 formed on the second surface of the substrate 110, and a first land. And a conductor 114 that connects the portion 111 and the second land portion 112. The conductor 114 is formed by filling the via hole 113 with a conductive paste and curing the conductive paste. The surface 115 of the conductor 114 is processed flat.
　また、特許文献２にもフレキシブルプリント配線板が開示されているが、導電体２１０の形状が図８のフレキシブルプリント配線板とは異なる。図９に示すように、ブラインドビア２００の導電体２１０の表面２１１には、窪み２１２が設けられている。 Moreover, although the flexible printed wiring board is disclosed also in patent document 2, the shape of the conductor 210 is different from the flexible printed wiring board of FIG. As shown in FIG. 9, a depression 212 is provided on the surface 211 of the conductor 210 of the blind via 200.
特開２０１１－２３６７６号公報JP 2011-23676 A 特開２００８－１０３５４８号公報JP 2008-103548 A
　フレキシブルプリント配線板は、曲げた状態で配置されたり、繰り返し曲げられるたりする。フレキシブルプリント配線板が曲げられるとき、ブラインドビアに力が加わる。そのため、導電層と導電体との間の接着力よりも導電層と導電体とに加わる応力が大きくなると、導電層から導電体が剥離する。導電層と導電体との間の剥離はブラインドビアの接触抵抗を増大させ、フレキシブルプリント配線板を用いた電気回路の信頼性を低下させる。このようなことから、フレキシブルプリント配線板の曲げにより導電体と導電層との間の接触抵抗が増大しないことが要求される。 ¡Flexible printed circuit boards are placed in a bent state or bent repeatedly. When the flexible printed wiring board is bent, a force is applied to the blind via. Therefore, when the stress applied to the conductive layer and the conductor becomes larger than the adhesive force between the conductive layer and the conductor, the conductor peels from the conductive layer. Peeling between the conductive layer and the conductor increases the contact resistance of the blind via and reduces the reliability of the electric circuit using the flexible printed wiring board. For this reason, it is required that the contact resistance between the conductor and the conductive layer does not increase due to bending of the flexible printed wiring board.
　しかし、上記のいずれの文献にも、フレキシブルプリント配線板の曲げに起因して、ブラインドビアの接触抵抗が増大するということについては、記載されていない。また、このような課題に対する技術、すなわち、フレキシブルプリント配線板の曲げに起因するブラインドビアの接触抵抗の増大を抑制する技術についても、開示されていない。 However, none of the above documents describes that the contact resistance of the blind via increases due to the bending of the flexible printed wiring board. Further, there is no disclosure of a technique for such a problem, that is, a technique for suppressing an increase in the contact resistance of the blind via caused by bending of the flexible printed wiring board.
　本発明はこのような課題を解決するためになされたものであり、その目的は、曲げに対してブラインドビアの接触抵抗の増大を抑制することのできるフレキシブルプリント配線板、およびそのフレキシブルプリント配線板の製造方法を提供することにある。 The present invention has been made to solve such problems, and an object of the present invention is to provide a flexible printed wiring board capable of suppressing an increase in the contact resistance of a blind via against bending, and the flexible printed wiring board. It is in providing the manufacturing method of.
　（１）本発明の第１の態様によれば、基材と、前記基材の第１面に形成された第１導電層と、前記基材の第２面に形成された第２導電層と、前記第１導電層と前記第２導電層とを接続する導電体とを備えるフレキシブルプリント配線板が提供される。そのフレキシブルプリント配線板は、前記第１導電層に設けられた第１ランド部と、前記第２導電層において前記基材を挟んで前記第１ランド部の反対側に設けられた第２ランド部と、前記第１ランド部および前記基材を貫通して前記第２ランド部に達するビア孔とを備えている。前記導電体は、導電ペーストにより形成されたものであって、前記導電体は、前記ビア孔の底面の全部を覆うようにこのビア孔を充たし、かつ前記第１ランド部の表面の少なくとも一部を覆うように形成され、前記ビア孔の中心軸上における前記導電体の厚さは、前記基材の厚さと前記第１ランド部の厚さとの和よりも小さい。 (1) According to the first aspect of the present invention, the base material, the first conductive layer formed on the first surface of the base material, and the second conductive layer formed on the second surface of the base material. And a flexible printed wiring board provided with the conductor which connects a said 1st conductive layer and a said 2nd conductive layer is provided. The flexible printed wiring board includes a first land portion provided on the first conductive layer and a second land portion provided on the opposite side of the first land portion with the base material sandwiched between the second conductive layers. And a via hole penetrating the first land portion and the base material and reaching the second land portion. The conductor is formed of a conductive paste, and the conductor fills the via hole so as to cover the entire bottom surface of the via hole, and at least a part of the surface of the first land portion. And the thickness of the conductor on the central axis of the via hole is smaller than the sum of the thickness of the base material and the thickness of the first land portion.
　第１ランド部を外側にしてフレキシブルプリント配線板を曲げると、基材の外面が延びるとともに内面が縮む。このとき、第１ランド部と導電体とが離間する方向に力が加わる。この結果、導電体と第１ランド部との間に隙間が生じ、ブラインドビアの接触抵抗が増大する。ブラインドビアの接触抵抗の増大の程度は、ブラインドビアを構成する導電体の構造に依存する。 When the flexible printed wiring board is bent with the first land portion outside, the outer surface of the substrate extends and the inner surface contracts. At this time, force is applied in a direction in which the first land portion and the conductor are separated from each other. As a result, a gap is generated between the conductor and the first land portion, and the contact resistance of the blind via is increased. The degree of increase in the contact resistance of the blind via depends on the structure of the conductor constituting the blind via.
　本発明の第１の態様では、このような点を考慮し、導電体が変形しやすい構造を採用している。すなわち、ビア孔の中心軸上の導電体の厚さを、基材の厚さと第１ランド部の厚さとの和よりも小さくする。具体的には、導電体において、ビア孔の中心軸上に窪みを設け、導電体を変形しやすくし、基材の変形に追従して導電体が変形しやすい構造を構成している。これにより、フレキシブルプリント配線板の曲げに対するブラインドビアの接触抵抗の増大を抑制することができる。なお、上記「ビア孔の中心軸」とは、ビア孔の底面の中心点を通過しかつ底面に垂直に延びる軸である。 In the first aspect of the present invention, in consideration of such points, a structure in which the conductor is easily deformed is adopted. That is, the thickness of the conductor on the central axis of the via hole is made smaller than the sum of the thickness of the base material and the thickness of the first land portion. Specifically, in the conductor, a recess is provided on the central axis of the via hole so that the conductor is easily deformed, and the conductor is easily deformed following the deformation of the base material. Thereby, increase of the contact resistance of the blind via | veer with respect to the bending of a flexible printed wiring board can be suppressed. The “central axis of the via hole” is an axis that passes through the center point of the bottom surface of the via hole and extends perpendicularly to the bottom surface.
　（２）前記ビア孔の中心軸上における前記導電体の厚さは５μｍ以上であることが望ましい。 (2) The thickness of the conductor on the central axis of the via hole is preferably 5 μm or more.
　フレキシブルプリント配線板を曲げると導電体が変形する。導電体が薄いとき、導電体に亀裂が生じる可能性が高くなる。そこで、導電体の厚さを５μｍ以上とすれば、ビア孔の中心軸上の導電体の厚さを５μｍ未満とする場合に比べ、導電体に亀裂が発生することを抑制することができる。 ¡The conductor is deformed when the flexible printed wiring board is bent. When the conductor is thin, there is a high possibility that the conductor will crack. Therefore, if the thickness of the conductor is 5 μm or more, it is possible to suppress the occurrence of cracks in the conductor as compared with the case where the thickness of the conductor on the central axis of the via hole is less than 5 μm.
　（３）前記導電体のうち前記第１ランド部を覆う部分の最も厚い箇所の厚さが２μｍ以上であることが望ましい。第１ランド部を覆う部分に亀裂が生じるとき、導電体と第１ランド部との間の接触抵抗が増大する。この点を考慮し、第１ランド部を覆う部分の最も厚い箇所の厚さが２μｍ以上であれば、第１ランド部を覆う部分に亀裂が発生することを抑制することができる。 (3) It is desirable that the thickness of the thickest portion of the conductor covering the first land portion is 2 μm or more. When a crack occurs in the portion covering the first land portion, the contact resistance between the conductor and the first land portion increases. Considering this point, if the thickness of the thickest portion covering the first land portion is 2 μm or more, the occurrence of cracks in the portion covering the first land portion can be suppressed.
　（４）前記ビア孔の中心軸に対し垂直でありかつ前記第１ランド部の表面を含む面で前記導電体を切断したときの前記導電体の断面において、この断面の内円と外円との間の距離は５μｍ以上であることが望ましい。 (4) In a cross section of the conductor when the conductor is cut by a plane perpendicular to the central axis of the via hole and including the surface of the first land portion, an inner circle and an outer circle of the cross section The distance between is preferably 5 μm or more.
　導電体においてビア孔の開口部に対応する部分は、亀裂が生じやすい。この点を考慮し、前記導電体の断面の内円と外円との間の距離を５μｍ以上とすれば、ビア孔の第１ランド部側の開口部に対応する部分において、亀裂が発生することを抑制することができる。 The portion of the conductor corresponding to the opening of the via hole is likely to crack. Considering this point, if the distance between the inner circle and the outer circle of the cross section of the conductor is set to 5 μm or more, a crack occurs in a portion corresponding to the opening on the first land side of the via hole. This can be suppressed.
　（５）前記導電体は、扁平球状の導電粒子およびこれらの結合体を含むことが望ましい。導電体を構成する導電粒子の表面に突起があるとき、導電粒子間の隙間が多くなる。一方、導電粒子が扁平球状であるとき、導電粒子同士の空隙は小さくなる。この点を考慮し、導電体を扁平球状の導電粒子により構成し、導電粒子の密度を大きくすれば、ブラインドビアの許容電流量を高くすることができる。 (5) The conductor preferably includes flat spherical conductive particles and a combination thereof. When there are protrusions on the surface of the conductive particles constituting the conductor, the gaps between the conductive particles increase. On the other hand, when the conductive particles are flat spherical, the gap between the conductive particles is small. Considering this point, if the conductor is composed of flat spherical conductive particles and the density of the conductive particles is increased, the allowable current amount of the blind via can be increased.
　（６）本発明の第２の態様によれば、基材と、前記基材の第１面に形成された第１導電層と、前記基材の第２面に形成された第２導電層と、前記第１導電層と前記第２導電層とを接続する導電体とを備えるフレキシブルプリント配線板の製造方法が提供される。その方法では、下記の（１）式で示されるチクソトロピー指数が０．２５以下の導電ペーストを用いて前記導電体を形成することを含んでいる。 (6) According to the second aspect of the present invention, the base material, the first conductive layer formed on the first surface of the base material, and the second conductive layer formed on the second surface of the base material. And a method of manufacturing a flexible printed wiring board comprising a conductor connecting the first conductive layer and the second conductive layer. The method includes forming the conductor using a conductive paste having a thixotropy index of 0.25 or less represented by the following formula (1).
　チクソトロピー指数
＝ｌｏｇ（η１／η２）／ｌｏｇ（Ｄ２／Ｄ１）・・・（１）
　ここで、η１はせん断速度Ｄ１が２ｓ－１のときの前記導電ペーストの粘度を示し、η２はせん断速度Ｄ２が２０ｓ－１のときの前記導電ペーストの粘度を示す。 Thixotropic index = log (η1 / η2) / log (D2 / D1) (1)
Here, η1 indicates the viscosity of the conductive paste when the shear rate D1 is 2 s −1 , and η2 indicates the viscosity of the conductive paste when the shear rate D2 is 20 s −1 .
　従来の導電ペーストによれば、導電体の上部が表面張力により盛り上がる。一方、本発明の導電ペーストによれば、導電体の上部の中央部分を窪ませることができる。これは次の理由による。 According to the conventional conductive paste, the upper part of the conductor is raised by the surface tension. On the other hand, according to the electrically conductive paste of this invention, the center part of the upper part of a conductor can be depressed. This is due to the following reason.
　導電ペーストは、せん断応力を加えない状態に近づくにしたがって、粘度が増大するという性質、すなわち、チキソトロピー性を備えている。チクソトロピー指数は、その値が小さいほど、チクソトロピー性が低いことを示す。すなわち、チクソトロピー指数が０．２５以下の導電ペーストを基材に塗布した後には、その導電ペーストを流動させることができるため、導電体の上部の中央部分に窪みを形成することができる。 The conductive paste has a property that the viscosity increases as it approaches a state where no shear stress is applied, that is, thixotropic property. The thixotropy index indicates that the smaller the value, the lower the thixotropy. That is, after applying a conductive paste having a thixotropy index of 0.25 or less to a substrate, the conductive paste can be flowed, so that a depression can be formed in the upper central portion of the conductor.
　（７）フレキシブルプリント配線板の製造方法において、扁平球状の導電粒子を含みかつこの扁平球状の導電粒子の質量比が７０質量％以上である導電ペーストを用いて、前記導電体を形成することが望ましい。この場合、導電体の上部の中央部分を窪ませることができる。 (7) In the method for producing a flexible printed wiring board, the conductor may be formed using a conductive paste containing flat spherical conductive particles and having a mass ratio of the flat spherical conductive particles of 70% by mass or more. desirable. In this case, the upper central portion of the conductor can be recessed.
　（８）フレキシブルプリント配線板の製造方法において、前記導電ペーストは、平均粒径が３０ｎｍ以上２００ｎｍ以下の球状の導電粒子を更に含むことが望ましい。この場合、導電体の上部の中央部分を窪ませることができる。 (8) In the method for manufacturing a flexible printed wiring board, it is preferable that the conductive paste further includes spherical conductive particles having an average particle size of 30 nm to 200 nm. In this case, the upper central portion of the conductor can be recessed.
　平均粒径が３０ｎｍ以上２００ｎｍ以下の球状の導電粒子を導電ペーストに含む場合、これら導電粒子は、扁平球状または球状の導電粒子の間の隙間に入るため、導電体の導電粒子密度を高くすることができる。これにより、ブラインドビアの最大許容電流量を高くすることができる。 When spherical conductive particles having an average particle size of 30 nm to 200 nm are included in the conductive paste, these conductive particles enter the gaps between the flat spherical or spherical conductive particles, so that the conductive particle density of the conductor is increased. Can do. Thereby, the maximum allowable current amount of the blind via can be increased.
　（９）前記導電ペーストには、前記扁平球状の導電粒子として、平均粒径が１．４μｍ以上３．３μｍ以下の第１導電粒子と、平均粒径が０．５μｍ以上１．８μｍ以下の第２導電粒子とが含まれることが望ましい。この場合、導電体の上部の中央部分を窪ませることができる。 (9) The conductive paste includes, as the flat spherical conductive particles, first conductive particles having an average particle size of 1.4 μm or more and 3.3 μm or less, and first conductive particles having an average particle size of 0.5 μm or more and 1.8 μm or less. 2 conductive particles are desirably included. In this case, the upper central portion of the conductor can be recessed.
　また、平均粒径が１．４μｍ以上３．３μｍ以下の導電粒子を導電ペーストに含めることから、次の効果が得られる。すなわち、１．４μｍ以上３．３μｍ以下の導電粒子は、導電ペーストの膜厚を大きくする。これにより、導電ペーストの膜厚が小さくなりすぎることを抑制することができる。なお、平均粒径が３．３μｍよりも大きい導電粒子を導電ペーストに含めると、膜厚が厚くなりすぎる。 In addition, since conductive particles having an average particle size of 1.4 μm or more and 3.3 μm or less are included in the conductive paste, the following effects can be obtained. That is, conductive particles having a size of 1.4 μm or more and 3.3 μm or less increase the thickness of the conductive paste. Thereby, it can suppress that the film thickness of an electrically conductive paste becomes small too much. If conductive particles having an average particle size larger than 3.3 μm are included in the conductive paste, the film thickness becomes too thick.
　本発明によれば、曲げに対してブラインドビアの接触抵抗の増大を抑制することのできるフレキシブルプリント配線板、およびそのフレキシブルプリント配線板の製造方法を提供することができる。 According to the present invention, it is possible to provide a flexible printed wiring board capable of suppressing an increase in the contact resistance of the blind via against bending and a method for manufacturing the flexible printed wiring board.
実施形態のフレキシブルプリント配線板の断面図である。It is sectional drawing of the flexible printed wiring board of embodiment. ブラインドビアの断面図である。It is sectional drawing of a blind via. （ａ）は導電粒子の斜視図、（ｂ）は導電粒子の平面図、（ｃ）は図３（ｂ）の３Ｃ－３Ｃ線に沿う断面図である。(A) is a perspective view of conductive particles, (b) is a plan view of conductive particles, and (c) is a cross-sectional view taken along line 3C-3C in FIG. 3 (b). 従来構造のブラインドビアの断面構造を示す断面図である。It is sectional drawing which shows the cross-section of the blind via of the conventional structure. 実施形態のブラインドビアの断面構造を示す断面図である。It is sectional drawing which shows the cross-section of the blind via of embodiment. （ａ）フレキシブルプリント配線板の平面図、（ｂ）フレキシブルプリント配線板の断面図である。(A) The top view of a flexible printed wiring board, (b) It is sectional drawing of a flexible printed wiring board. 曲げ試験を説明する模式図である。It is a schematic diagram explaining a bending test. 従来のフレキシブルプリント配線板の断面図である。It is sectional drawing of the conventional flexible printed wiring board. 従来のフレキシブルプリント配線板の断面図である。It is sectional drawing of the conventional flexible printed wiring board.
フレキシブルプリント配線板
　図１を参照して、フレキシブルプリント配線板１について説明する。 Flexible Printed Wiring Board The flexible printed wiring board 1 will be described with reference to FIG.
　フレキシブルプリント配線板１は、基材３０と、基材３０の第１面３１に形成された第１導電パターン１０（第１導電層）と、基材３０の第２面３２に形成された第２導電パターン２０（第２導電層）と、第１導電パターン１０と第２導電パターン２０とを接続する導電体４０とを備える。基材３０の第２面３２は第１面３１とは反対側に位置する。 The flexible printed wiring board 1 includes a base material 30, a first conductive pattern 10 (first conductive layer) formed on the first surface 31 of the base material 30, and a second surface 32 of the base material 30. 2 conductive pattern 20 (2nd conductive layer), and the conductor 40 which connects the 1st conductive pattern 10 and the 2nd conductive pattern 20 are provided. The second surface 32 of the substrate 30 is located on the side opposite to the first surface 31.
　基材３０は、可撓性を有する絶縁フィルムにより形成されている。 The base material 30 is formed of a flexible insulating film.
　例えば、基材３０は、ポリイミド、ポリエチレンテレフタレート等により形成されている。基材３０の厚さはフレキシブルプリント配線板１の用途に応じて適宜選択される。具体的には、５μｍ～５０μｍ厚の基材３０が採用される。 For example, the base material 30 is made of polyimide, polyethylene terephthalate, or the like. The thickness of the base material 30 is appropriately selected according to the use of the flexible printed wiring board 1. Specifically, a substrate 30 having a thickness of 5 μm to 50 μm is employed.
　各導電パターン１０，２０は、基材３０の金属層を加工することにより形成される。例えば、両面銅張積層板をエッチングすることにより各導電パターン１０，２０が形成される。なお、両面銅張積層板に代えて、両面がめっき層の基板を用いてもよい。 Each conductive pattern 10 and 20 is formed by processing the metal layer of the base material 30. For example, the conductive patterns 10 and 20 are formed by etching a double-sided copper-clad laminate. In addition, it may replace with a double-sided copper clad laminated board, and may use the board | substrate with a plating layer on both surfaces.
　第１導電パターン１０の厚さはフレキシブルプリント配線板１の用途に応じて適宜選択される。第２導電パターン２０は、第１導電パターン１０と同様に形成される。 The thickness of the first conductive pattern 10 is appropriately selected according to the use of the flexible printed wiring board 1. The second conductive pattern 20 is formed in the same manner as the first conductive pattern 10.
　図２を参照して、第１導電パターン１０と第２導電パターン２０とを接続するブラインドビア５０について説明する。ブラインドビア５０は、第１ランド部１１と、第２ランド部２１と、これらランド部１１，２１を接続する導電体４０とを含む。 Referring to FIG. 2, the blind via 50 that connects the first conductive pattern 10 and the second conductive pattern 20 will be described. The blind via 50 includes a first land portion 11, a second land portion 21, and a conductor 40 that connects the land portions 11 and 21.
　第１ランド部１１は、円形であり、その中心部にランド孔１１ｂが形成されている。第１ランド部１１の直径は、例えば、３００μｍ～１０００μｍに設定される。第１ランド部１１は第１導電パターン１０の一部である。 The first land portion 11 is circular, and a land hole 11b is formed at the center thereof. The diameter of the first land portion 11 is set to 300 μm to 1000 μm, for example. The first land portion 11 is a part of the first conductive pattern 10.
　第２ランド部２１は、基材３０を挟んで第１ランド部１１の反対側に設けられている。第２ランド部２１は円形に形成される。第２ランド部２１の直径は、１００μｍ～１０００μｍに設定される。第２ランド部２１は、第２導電パターン２０の一部である。第１ランド部１１および第２ランド部２１の形状は円形に限定されるべきものではなく、矩形でもよい。 The second land portion 21 is provided on the opposite side of the first land portion 11 with the base material 30 interposed therebetween. The second land portion 21 is formed in a circular shape. The diameter of the second land portion 21 is set to 100 μm to 1000 μm. The second land portion 21 is a part of the second conductive pattern 20. The shape of the 1st land part 11 and the 2nd land part 21 should not be limited to circular, A rectangle may be sufficient.
　第１ランド部１１および基材３０には、第２ランド部２１に至るまで第１ランド部１１および基材３０を貫通するビア孔３３が形成されている。ビア孔３３の底面３３ｂは第２ランド部２１の内面に対応する。ビア孔３３の底面３３ｂは略円形である。ビア孔３３は、例えばレーザ照射により形成される。ビア孔３３の直径は例えば２０μｍ～３００μｍとされる。ランド孔１１ｂは、ビア孔３３の一部を構成する。 The first land portion 11 and the base material 30 are formed with via holes 33 penetrating the first land portion 11 and the base material 30 up to the second land portion 21. The bottom surface 33 b of the via hole 33 corresponds to the inner surface of the second land portion 21. The bottom surface 33b of the via hole 33 is substantially circular. The via hole 33 is formed by, for example, laser irradiation. The diameter of the via hole 33 is, for example, 20 μm to 300 μm. The land hole 11 b constitutes a part of the via hole 33.
　導電体４０は、ビア孔３３の底面３３ｂの全部を覆うように、このビア孔３３を充たしている。導電体４０は第１ランド部１１の表面１１ａの一部または全部を覆っている。導電体４０の底部４２は第２ランド部２１に接触している。導電体４０の上部４１は第１ランド部１１に接触している。導電体４０の上部４１の中央部分には窪み４４が存在している。 The conductor 40 fills the via hole 33 so as to cover the entire bottom surface 33 b of the via hole 33. The conductor 40 covers part or all of the surface 11 a of the first land portion 11. The bottom portion 42 of the conductor 40 is in contact with the second land portion 21. The upper portion 41 of the conductor 40 is in contact with the first land portion 11. A depression 44 exists in the central portion of the upper portion 41 of the conductor 40.
　導電体４０の底部４２は、ビア孔３３の中心軸方向Ｄａにおいて第２導電パターン２０に接触している。導電体４０の上部４１は、ビア孔３３の中心軸方向Ｄａにおいて第１導電パターン１０に接触し、第１ランド部１１を部分的に覆う部分を含む。 The bottom portion 42 of the conductor 40 is in contact with the second conductive pattern 20 in the central axis direction Da of the via hole 33. The upper portion 41 of the conductor 40 includes a portion that contacts the first conductive pattern 10 in the central axis direction Da of the via hole 33 and partially covers the first land portion 11.
　ビア孔３３の中心軸Ｃａ上における導電体４０の厚さｔｄは、基材３０の厚さｔａと第１ランド部１１の厚さｔｂとの和よりも小さい。また、ビア孔３３の中心軸Ｃａ上における導電体４０の厚さｔｄは５μｍ以上とされる。導電体４０のうち第１ランド部１１を覆う部分の最も厚い箇所の厚さｔｅは、２μｍ以上である。ビア孔３３の中心軸Ｃａに対し垂直でありかつ第１ランド部１１の表面１１ａを含む面に沿って、導電体４０を切断したときの導電体４０の断面において、この断面の内円と外円（ビア孔３３）との間の距離Ｄｆは５μｍ以上である。 The thickness td of the conductor 40 on the central axis Ca of the via hole 33 is smaller than the sum of the thickness ta of the base material 30 and the thickness tb of the first land portion 11. Further, the thickness td of the conductor 40 on the central axis Ca of the via hole 33 is set to 5 μm or more. The thickness te of the thickest portion of the conductor 40 that covers the first land portion 11 is 2 μm or more. In the cross section of the conductor 40 when the conductor 40 is cut along a plane that is perpendicular to the central axis Ca of the via hole 33 and includes the surface 11a of the first land portion 11, an inner circle and an outer portion of the cross section of the conductor 40 are cut. The distance Df between the circle (via hole 33) is 5 μm or more.
　次に、導電体４０の構成材料について説明する。 Next, the constituent material of the conductor 40 will be described.
　導電体４０は、導電粒子６０およびバインダ樹脂を含む導電ペーストにより形成されている。すなわち、導電体４０は、導電粒子６０およびこれらの導電粒子６０を結合する結合体を含む構造体である。導電粒子６０同士は接触部分で溶融結合または焼結結合する。導電粒子６０同士が単に接触している部分もある。導電粒子６０は、バインダ樹脂により互いに固定されている。バインダ樹脂は加熱硬化時に収縮するため、導電粒子６０同士は互いに押圧された状態で存在している。 The conductor 40 is formed of a conductive paste containing conductive particles 60 and a binder resin. That is, the conductor 40 is a structure including the conductive particles 60 and a combined body that couples the conductive particles 60. The conductive particles 60 are melt bonded or sintered bonded at the contact portion. There is also a portion where the conductive particles 60 are simply in contact with each other. The conductive particles 60 are fixed to each other with a binder resin. Since the binder resin shrinks during heat curing, the conductive particles 60 are present in a state where they are pressed against each other.
　バインダ樹脂は熱硬化性樹脂であり、導電体４０においては硬化物として存在する。導電ペーストに含まれる導電粒子６０の一部もしくは全部は、球を扁平化した形状（以下、「扁平球状」という。）の金属粒子であり、導電体４０においては互いに結合した結合体として存在する。金属粒子は銀、銅またはニッケル等により形成されている。 The binder resin is a thermosetting resin and exists as a cured product in the conductor 40. Part or all of the conductive particles 60 included in the conductive paste are metal particles having a flattened sphere shape (hereinafter referred to as “flattened spherical shape”), and in the conductor 40, they exist as a bonded body. . The metal particles are made of silver, copper, nickel or the like.
　図３（ａ）～（ｃ）を参照して、典型的な扁平球状の導電粒子６０について説明する。図３（ａ）は導電粒子６０の斜視図を示す。図３（ｂ）は導電粒子６０を回転対称軸Ｃｒに沿う方向（以下、回転対称軸方向Ｄｒ）から見た平面図を示す。図３（ｃ）は導電粒子６０の断面図を示す。 A typical flat spherical conductive particle 60 will be described with reference to FIGS. FIG. 3A shows a perspective view of the conductive particles 60. FIG. 3B is a plan view of the conductive particles 60 viewed from a direction along the rotational symmetry axis Cr (hereinafter, rotational symmetry axis direction Dr). FIG. 3C shows a cross-sectional view of the conductive particles 60.
　導電粒子６０を回転対称軸方向Ｄｒから見た形状は略円形（円形に近似される形状）である。回転対称軸Ｃｒを含む面で導電粒子６０を切断したときの断面は、円を押しつぶした形状である。この断面の短辺Ｌｘと長辺Ｌｙとの比率（短辺Ｌｘ／長辺Ｌｙ）は、０．２以上１．０未満である。このような扁平球状の導電粒子６０は、球状の金属粒子を押圧機等で押し潰すことにより形成される。 The shape of the conductive particles 60 viewed from the rotationally symmetric axis direction Dr is substantially circular (a shape approximated to a circle). The cross section when the conductive particles 60 are cut along the plane including the rotational symmetry axis Cr is a shape obtained by crushing a circle. The ratio of the short side Lx to the long side Ly (short side Lx / long side Ly) of the cross section is 0.2 or more and less than 1.0. Such flat spherical conductive particles 60 are formed by crushing spherical metal particles with a pressing machine or the like.
　図４および図５を参照して、フレキシブルプリント配線板１の曲げに対するブラインドビア５０の作用について、従来構造のブラインドビア３５０（図４参照）を有するフレキシブルプリント配線板３００と比較して説明する。従来構造のブラインドビア３５０とはビア孔３３３の中心軸Ｃｂ上に窪み４４のないものを示す。 4 and 5, the action of the blind via 50 on the bending of the flexible printed wiring board 1 will be described in comparison with the flexible printed wiring board 300 having the blind via 350 having a conventional structure (see FIG. 4). The blind via 350 having a conventional structure is one having no depression 44 on the central axis Cb of the via hole 333.
　従来構造のフレキシブルプリント配線板３００を曲げたとき、ブラインドビア３５０には次のように力が作用する。図４に示すように、導電体３４０の上部３４１を外側にした状態でフレキシブルプリント配線板３００を曲げると、基材３３０、第１ランド部３１１、第２ランド部３２１、および導電体３４０のそれぞれに応力が発生する。 When the flexible printed wiring board 300 having the conventional structure is bent, a force acts on the blind via 350 as follows. As shown in FIG. 4, when the flexible printed wiring board 300 is bent with the upper portion 341 of the conductor 340 facing outside, each of the base material 330, the first land portion 311, the second land portion 321, and the conductor 340 is formed. Stress is generated.
　第１に、第１ランド部３１１の表面３１１ａと導電体３４０との境界面に沿って、せん断応力Ｆｘが発生する。第２に、ビア孔３３３の内側周面３３３ａと導電体３４０との境界面に垂直な方向に垂直応力Ｆｙが発生する。第３に、導電体３４０の上部３４１に引張応力Ｆｚが発生する。 First, a shear stress Fx is generated along the boundary surface between the surface 311a of the first land portion 311 and the conductor 340. Second, a vertical stress Fy is generated in a direction perpendicular to the boundary surface between the inner peripheral surface 333a of the via hole 333 and the conductor 340. Third, a tensile stress Fz is generated in the upper part 341 of the conductor 340.
　フレキシブルプリント配線板３００の曲げが小さいときは、導電体３４０の上部３４１は基材３３０に追従して変形する。すなわち、フレキシブルプリント配線板３００の曲げが小さいときは、せん断応力Ｆｘが第１ランド部３１１の表面３１１ａと導電体３４０との間の接着力よりも小さく、または、垂直応力Ｆｙがビア孔３３３の内側周面３３３ａと導電体３４０との間の接着力よりも小さいため、導電体３４０が第１ランド部３１１から剥離しない。 When the bending of the flexible printed wiring board 300 is small, the upper part 341 of the conductor 340 is deformed following the base material 330. That is, when the bending of the flexible printed wiring board 300 is small, the shear stress Fx is smaller than the adhesive force between the surface 311 a of the first land portion 311 and the conductor 340, or the vertical stress Fy is the via hole 333. Since it is smaller than the adhesive force between the inner peripheral surface 333a and the conductor 340, the conductor 340 does not peel from the first land portion 311.
　一方、フレキシブルプリント配線板３００の曲げが所定の曲率よりも大きくなるとき、導電体３４０の上部３４１が第１ランド部３１１から剥離する。すなわち、フレキシブルプリント配線板３００の曲げが大きいとき、導電体３４０の上部３４１が大きく曲げられ、歪δが大きくなり、導電体３４０の上部３４１に加わる引張応力Ｆｚが大きくなる。この結果、せん断応力Ｆｘが第１ランド部３１１の表面３１１ａと導電体３４０との間の接着力よりも大きくなるとともに垂直応力Ｆｙがビア孔３３３の内側周面３３３ａと導電体３４０との間の接着力よりも大きくなるため、図４に示すように、第１ランド部３１１から導電体３４０の上部３４１が剥離する。 On the other hand, when the bending of the flexible printed wiring board 300 becomes larger than a predetermined curvature, the upper portion 341 of the conductor 340 is peeled from the first land portion 311. That is, when the bending of the flexible printed wiring board 300 is large, the upper portion 341 of the conductor 340 is greatly bent, the strain δ increases, and the tensile stress Fz applied to the upper portion 341 of the conductor 340 increases. As a result, the shear stress Fx becomes larger than the adhesive force between the surface 311a of the first land portion 311 and the conductor 340, and the vertical stress Fy is between the inner peripheral surface 333a of the via hole 333 and the conductor 340. Since it becomes larger than the adhesive force, the upper portion 341 of the conductor 340 is peeled from the first land portion 311 as shown in FIG.
　このような剥離は、フレキシブルプリント配線板３００の曲げが所定の曲率よりも小さくても、曲げの頻度が多いときには、生じる。曲げの頻度が多いとき、第１ランド部３１１の表面３１１ａと導電体３４０との接着部分に繰り返しせん断応力Ｆｘが加わるため、当該接着部分の接着力が徐々に低下して剥離が発生する。 Such peeling occurs when the bending of the flexible printed wiring board 300 is smaller than a predetermined curvature but the bending frequency is high. When the bending frequency is high, since the shear stress Fx is repeatedly applied to the bonding portion between the surface 311a of the first land portion 311 and the conductor 340, the bonding force of the bonding portion gradually decreases and peeling occurs.
　それに対し、本実施形態のフレキシブルプリント配線板１を曲げたときは、ブラインドビア５０に次のように力が作用する。フレキシブルプリント配線板１の曲げが小さいとき、導電体４０の上部４１は基材３０に追従して変形する。すなわち、フレキシブルプリント配線板１の曲げが小さいときにブラインドビア５０に加わる力は、従来構造のブラインドビア３５０に対する作用と殆ど変わらない。 On the other hand, when the flexible printed wiring board 1 of the present embodiment is bent, a force acts on the blind via 50 as follows. When the bending of the flexible printed wiring board 1 is small, the upper portion 41 of the conductor 40 is deformed following the base material 30. That is, the force applied to the blind via 50 when the bending of the flexible printed wiring board 1 is small is almost the same as the effect on the blind via 350 having the conventional structure.
　一方、フレキシブルプリント配線板１を、従来構造のフレキシブルプリント配線板３００において剥離が生じる曲率（以下、「従来限界曲率Ｒｘ」）まで曲げたときは、従来構造のフレキシブルプリント配線板３００とは異なり、導電体４０の上部４１が基材３０に追従して変形する。この結果、第１ランド部１１からの導電体４０の剥離は生じない。 On the other hand, when the flexible printed wiring board 1 is bent to a curvature at which peeling occurs in the flexible printed wiring board 300 having the conventional structure (hereinafter referred to as “conventional limit curvature Rx”), unlike the flexible printed wiring board 300 having the conventional structure, The upper portion 41 of the conductor 40 is deformed following the base material 30. As a result, no peeling of the conductor 40 from the first land portion 11 occurs.
　以下、この理由を説明する。 The reason for this will be explained below.
　フレキシブルプリント配線板１の曲げが大きくなるとき、導電体４０の上部４１が大きく曲げられるため、導電体４０の上部４１に加わる引張応力Ｆｚが大きくなるが、従来構造のブラインドビア３５０と比べて引張応力Ｆｚは小さい。 When the flexure of the flexible printed wiring board 1 is increased, the upper portion 41 of the conductor 40 is greatly bent, so that the tensile stress Fz applied to the upper portion 41 of the conductor 40 is increased. The stress Fz is small.
　これは、フレキシブルプリント配線板１の曲げにおける導電体４０の上部４１の歪δが小さいことによる。すなわち、導電体４０の上部４１は、従来構造のブラインドビア３５０と異なり、窪んでいる。このような窪み４４は、第２ランド部２１からの導電体４０の表面４３までの長さＬｓを従来構造のブラインドビア３５０に比べて短くする。導電体４０の表面部分の歪δの大きさは第２ランド部２１に近い程、小さくなるため、このような窪み４４の存在により、導電体４０の上部４１の歪δが小さくなる。 This is because the strain δ of the upper portion 41 of the conductor 40 when the flexible printed wiring board 1 is bent is small. That is, the upper portion 41 of the conductor 40 is recessed unlike the blind via 350 having a conventional structure. Such a depression 44 shortens the length Ls from the second land portion 21 to the surface 43 of the conductor 40 as compared with the blind via 350 having a conventional structure. Since the magnitude of the strain δ of the surface portion of the conductor 40 is smaller as it is closer to the second land portion 21, the strain δ of the upper portion 41 of the conductor 40 is reduced by the presence of such a depression 44.
　この結果、フレキシブルプリント配線板１が従来限界曲率Ｒｘまで曲げられるときでも、せん断応力Ｆｘが第１ランド部１１の表面１１ａと導電体４０との間の接着力よりも大きくなったり、垂直応力Ｆｙがビア孔３３の内側周面３３ａと導電体４０との間の接着力よりも大きくなったりすることが抑制される。このため、図５に示すように、導電体４０の上部４１が第１ランド部１１から剥離せず、導電体４０の上部４１が基材３０に追従して変形する。
フレキシブルプリント配線板の製造方法
　次に、フレキシブルプリント配線板１の製造方法について説明する。 As a result, even when the flexible printed wiring board 1 is bent to the conventional limit curvature Rx, the shear stress Fx becomes larger than the adhesive force between the surface 11a of the first land portion 11 and the conductor 40, or the vertical stress Fy. Is prevented from becoming larger than the adhesive force between the inner peripheral surface 33a of the via hole 33 and the conductor 40. For this reason, as shown in FIG. 5, the upper portion 41 of the conductor 40 does not peel from the first land portion 11, and the upper portion 41 of the conductor 40 is deformed following the base material 30.
Next, a method for manufacturing the flexible printed wiring board 1 will be described.
　第１工程では、エッチング法により基材３０の両面に導電パターン１０，２０を形成する。第１導電パターン１０にはランド部が含まれる。第２導電パターン２０には第２ランド部２１が含まれている。第１導電パターン１０のランド部は、次工程でレーザによりランド孔１１ｂが形成されることにより、第１ランド部１１に変更される。 In the first step, the conductive patterns 10 and 20 are formed on both surfaces of the base material 30 by an etching method. The first conductive pattern 10 includes a land portion. The second conductive pattern 20 includes a second land portion 21. The land portion of the first conductive pattern 10 is changed to the first land portion 11 by forming a land hole 11b by a laser in the next step.
　第２工程では、レーザによりビア孔３３が形成される。具体的には、第１導電パターン１０のランド部にレーザを照射することにより、ランド部および基材３０をともに貫通する孔（ビア孔３３）が形成される。 In the second step, the via hole 33 is formed by a laser. Specifically, by irradiating the land portion of the first conductive pattern 10 with a laser, a hole (via hole 33) penetrating both the land portion and the substrate 30 is formed.
　第３工程では、印刷法により導電ペーストがビア孔３３に充填される。充填後、導電ペーストが静止する安定な状態になるまで、導電ペーストが流動させられる。すなわち、ビア孔３３の中心部分が窪む状態になるまで、導電ペーストが流動させられる。具体的には、導電ペーストを充填した後の基材３０が室温で数分～数時間に亘って放置される。この後、基材３０が加熱され、導電ペーストを硬化させる。
導電ペースト
　次に、導電ペーストについて説明する。 In the third step, the via paste 33 is filled with the conductive paste by a printing method. After filling, the conductive paste is allowed to flow until the conductive paste is in a stable and static state. That is, the conductive paste is caused to flow until the central portion of the via hole 33 is depressed. Specifically, the base material 30 after filling with the conductive paste is left at room temperature for several minutes to several hours. Thereafter, the substrate 30 is heated to cure the conductive paste.
Conductive paste Next, the conductive paste will be described.
　導電ペーストは、ビア孔３３に充填された後、暫くの期間にわたって流動し、かつビア孔３３に沿って広がり過ぎない性質を有する。 The conductive paste has a property that after filling the via hole 33, it flows for a period of time and does not spread too much along the via hole 33.
　導電ペーストは、導電粒子と、バインダ樹脂と、溶剤とを含む。導電粒子としては、図３で示した扁平球状の金属粒子（表１の第２導電粒子に対応する。）が用いられる。例えば、導電粒子６０を、平面視したとき、すなわち、回転対称軸方向Ｄｒに沿った方向から見たときの平均粒径（直径）が０．５μｍ以上３．３μｍ以下である銀粒子が用いられる。この銀粒子の導電ペースト全体に対する質量比（以下、単に質量比というときも同じ意味である。）は、７０質量％以上とすることが好ましい。平均粒径とは、導電粒子６０の粒径（平面視の導電粒子６０の直径）の体積累積分布において、体積累積値で５０％の値に相当する粒径を示す。 The conductive paste contains conductive particles, a binder resin, and a solvent. As the conductive particles, the flat spherical metal particles (corresponding to the second conductive particles in Table 1) shown in FIG. 3 are used. For example, silver particles having an average particle diameter (diameter) of 0.5 μm or more and 3.3 μm or less when the conductive particles 60 are viewed in plan, that is, when viewed from a direction along the rotational symmetry axis direction Dr, are used. . The mass ratio of the silver particles to the entire conductive paste (hereinafter also simply referred to as mass ratio) is preferably 70% by mass or more. The average particle size indicates a particle size corresponding to a value of 50% in terms of a volume cumulative value in a volume cumulative distribution of the particle size of the conductive particles 60 (diameter of the conductive particles 60 in plan view).
　導電ペーストには、扁平球状の導電粒子として、平均粒径が異なる２種以上の導電粒子を含ませることが好ましい。例えば、平均粒径が０．５μｍ以上１．８μｍ以下である導電粒子（以下、第２導電粒子という。）と、平均粒径が１．４μｍ以上３．３μｍ以下の導電粒子（以下、第１導電粒子という。）とを導電ペーストに含める。 The conductive paste preferably contains two or more kinds of conductive particles having different average particle diameters as flat spherical conductive particles. For example, conductive particles having an average particle size of 0.5 μm to 1.8 μm (hereinafter referred to as second conductive particles) and conductive particles having an average particle size of 1.4 μm to 3.3 μm (hereinafter referred to as first particles). (Referred to as conductive particles) in the conductive paste.
　また、導電ペーストには、扁平球状の導電粒子６０の他、球状の導電粒子（以下、第３導電粒子という。）を存在させることが好ましい。球状の導電粒子としては、平均粒径が扁平球状の導電粒子６０の平均粒径よりも小さいことが好ましい。例えば、平均粒径３０ｎｍ以上２００ｎｍ以下の球状の導電粒子が用いられる。また、球状の導電粒子の質量比は、扁平球状の導電粒子６０の質量比よりも小さく設定される。例えば、球状の導電粒子の質量比は１．０質量％以上１５質量％以下に設定される。 Further, it is preferable that spherical conductive particles (hereinafter referred to as third conductive particles) be present in addition to the flat spherical conductive particles 60 in the conductive paste. The spherical conductive particles preferably have an average particle size smaller than the average particle size of the flat spherical conductive particles 60. For example, spherical conductive particles having an average particle size of 30 nm to 200 nm are used. The mass ratio of the spherical conductive particles is set smaller than the mass ratio of the flat spherical conductive particles 60. For example, the mass ratio of the spherical conductive particles is set to 1.0% by mass or more and 15% by mass or less.
　平均粒径が１．４μｍ以上３．３μｍ以下の導電粒子（第１導電粒子）としては、表面を金属で被覆したコーティング粒子を用いることもできる。例えば、銅粒子を銀で被覆した銀コート銅粒子を用いることができる。 As the conductive particles (first conductive particles) having an average particle size of 1.4 μm or more and 3.3 μm or less, coating particles whose surfaces are coated with metal can be used. For example, silver-coated copper particles in which copper particles are coated with silver can be used.
　バインダ樹脂としては、エポキシ樹脂、フェノール樹脂、ポリエステル樹脂、アクリル樹脂、メラミン樹脂、ポリイミド樹脂、ポリアミドイミド樹脂、フェノシキ樹脂等が用いられる。耐熱性を考慮する場合は、熱硬化性樹脂が採用される。特にエポキシ樹脂が好適である。 As the binder resin, epoxy resin, phenol resin, polyester resin, acrylic resin, melamine resin, polyimide resin, polyamideimide resin, phenoxy resin, or the like is used. When considering heat resistance, a thermosetting resin is employed. Epoxy resins are particularly suitable.
　エポキシ樹脂の種類は特に限定されない。 The type of epoxy resin is not particularly limited.
　例えば、ビスフェノールＡ、ビスフェノールＦ、ビスフェノールＳ、ビスフェノールＡＤ等を原料とするビスフェノール型エポキシ樹脂が用いられる。また、ナフタレン型エポキシ樹脂、ノボラック型エポキシ樹脂、ビフェニル型エポキシ樹脂、ジシクロペンタジエン型エポキシ樹脂等を用いることもできる。また、エポキシ樹脂には一液性のもの、二液性のものがあるが、いずれも用いることができる。 For example, a bisphenol type epoxy resin made from bisphenol A, bisphenol F, bisphenol S, bisphenol AD or the like is used. A naphthalene type epoxy resin, a novolac type epoxy resin, a biphenyl type epoxy resin, a dicyclopentadiene type epoxy resin, or the like can also be used. Epoxy resins include one-component and two-component epoxy resins, and any of them can be used.
　マイクロカプセル型の硬化剤を主剤（エポキシ樹脂）に分散させた一液性エポキシ樹脂を用いることもできる。マイクロカプセル型の硬化剤を均一に分散させるため、溶剤として、例えば、ブチルカルビトールアセテート、またはエチルカルビトールアセテートが用いられる。 It is also possible to use a one-component epoxy resin in which a microcapsule type curing agent is dispersed in a main agent (epoxy resin). In order to uniformly disperse the microcapsule type curing agent, for example, butyl carbitol acetate or ethyl carbitol acetate is used as a solvent.
　上記各種の導電粒子、バインダ樹脂、および溶剤については、次の（１）式を充たすように、それらの質量比が設定されている。 The mass ratio of the various conductive particles, the binder resin, and the solvent is set so as to satisfy the following expression (1).
　チクソトロピー指数　≦　０．２５・・・（１）
・チクソトロピー指数＝ｌｏｇ（η１／η２）／ｌｏｇ（Ｄ２／Ｄ１）
・η１は、せん断速度Ｄ１が２ｓ－１のときの導電ペーストの粘度（Ｐａ・ｓ）を示す。
・η２は、せん断速度Ｄ２が２０ｓ－１のときの導電ペーストの粘度（Ｐａ・ｓ）を示す。 Thixotropic index ≦ 0.25 (1)
Thixotropic index = log (η1 / η2) / log (D2 / D1)
Η1 indicates the viscosity (Pa · s) of the conductive paste when the shear rate D1 is 2 s −1 .
Η2 indicates the viscosity (Pa · s) of the conductive paste when the shear rate D2 is 20 s −1 .
　すなわち、（１）式が成立するように、導電粒子６０の平均粒径および質量比、導電ペーストに含める導電粒子６０の種類および種別数、バインダ樹脂の種類および質量比、溶剤の種類および質量比等が設定される。なお、導電粒子６０の種類とは、球状の導電粒子、扁平球状の導電粒子等、形状別の分類を示す。種別数とは、導電ペーストに含める導電粒子の種類の数を示す。 That is, the average particle diameter and mass ratio of the conductive particles 60, the type and number of types of the conductive particles 60 included in the conductive paste, the type and mass ratio of the binder resin, the type and mass ratio of the solvent so that the formula (1) is satisfied. Etc. are set. The type of the conductive particles 60 indicates a classification according to shape, such as spherical conductive particles and flat spherical conductive particles. The number of types indicates the number of types of conductive particles included in the conductive paste.
　このような導電ペーストは次の性質を有する。 Such a conductive paste has the following properties.
　ビア孔３３に充填された後、導電ペーストは暫くの間に亘って流動する。そして、導電ペーストの流動が止まるときには、ビア孔３３の中心軸Ｃａ上に窪み４４が形成される。 After the via hole 33 is filled, the conductive paste flows for a while. When the flow of the conductive paste stops, a recess 44 is formed on the central axis Ca of the via hole 33.
　このような性質は、導電粒子６０の形状の選択により実現することができる。以下、この点について説明する。 Such properties can be realized by selecting the shape of the conductive particles 60. Hereinafter, this point will be described.
　バインダ樹脂により導電ペーストの流動性を調整することができる。しかし、バインダ樹脂の導電ペースト全体に対する質量比は小さいため、流動性の調整幅は小さい。このため、バインダ樹脂の種類を選択することにより、チクソトロピー指数を調整することは難しい。 The fluidity of the conductive paste can be adjusted by the binder resin. However, since the mass ratio of the binder resin to the entire conductive paste is small, the fluidity adjustment range is small. For this reason, it is difficult to adjust the thixotropy index by selecting the type of binder resin.
　鱗片状の導電粒子６０を導電ペーストの主成分とする場合、鱗片状の導電粒子６０が互いに引っ掛かった状態で存在するため、導電ペーストの流動性が小さい。一方、球状の導電粒子６０を導電ペーストの主成分とする場合、球状の導電粒子６０同士の引っ掛かりがないため、導電ペーストの流動性が大きくなり、第１ランド部１１を超えて広がる虞がある。 When the scaly conductive particles 60 are the main component of the conductive paste, the fluidity of the conductive paste is small because the scaly conductive particles 60 are present in a state of being caught with each other. On the other hand, when the spherical conductive particles 60 are the main component of the conductive paste, since the spherical conductive particles 60 are not caught, the fluidity of the conductive paste increases and may spread beyond the first land portion 11. .
　そこで、導電ペーストの主成分として、平均粒径が０．５μｍ以上３．３μｍ以下でありかつ扁平球状の導電粒子６０を用いる。このような形状の導電粒子６０の採用により、上記に示す流動性および形態保持性が発現する。これは、扁平球状の導電粒子６０同士は互いの引っ掛かりが小さいため流動しやすいこと、及び、この流動にともなって扁平球状の導電粒子６０同士が密な状態かつ構造的に安定な状態に再配列されることに起因すると考えられる。 Therefore, flat spherical conductive particles 60 having an average particle size of 0.5 μm or more and 3.3 μm or less are used as the main component of the conductive paste. By adopting the conductive particles 60 having such a shape, the fluidity and shape retention shown above are exhibited. This is because the flat spherical conductive particles 60 are easy to flow because the mutual catching is small, and the flat spherical conductive particles 60 are rearranged into a dense and structurally stable state with this flow. It is thought that it is caused by being done.
　表１に、導電ペーストの例を挙げる。 Table 1 gives examples of conductive paste.
　導電ペースト１～４は、本実施形態のフレキシブルプリント配線板１の製造に好適である。特に、導電ペースト１～３は、本実施形態のフレキシブルプリント配線板１の製造に用いるのに特に好ましい。導電ペースト５は、比較対象の導電ペーストの一例である。 The conductive pastes 1 to 4 are suitable for manufacturing the flexible printed wiring board 1 of the present embodiment. In particular, the conductive pastes 1 to 3 are particularly preferable for use in manufacturing the flexible printed wiring board 1 of the present embodiment. The conductive paste 5 is an example of a conductive paste to be compared.
　以下、表１に示す各成分について説明する。 Hereinafter, each component shown in Table 1 will be described.
　第１導電粒子は、銀コート銅粒子であり、図３に示すような扁平球状を呈する。第１導電粒子の平均粒径（平面視における直径）は１．９μｍである。 The first conductive particles are silver-coated copper particles and have a flat spherical shape as shown in FIG. The average particle diameter (diameter in plan view) of the first conductive particles is 1.9 μm.
　第２導電粒子は、銀粒子であり、図３に示すような扁平球状を呈する。第２導電粒子の平均粒径は０．９μｍである。 The second conductive particles are silver particles and have a flat spherical shape as shown in FIG. The average particle size of the second conductive particles is 0.9 μm.
　第３導電粒子は、球状の銀粒子である。第３導電粒子の平均粒径は１００ｎｍである。 The third conductive particles are spherical silver particles. The average particle diameter of the third conductive particles is 100 nm.
　エポキシ樹脂は、分子量４５０００～５５０００のビスフェノールＡ型エポキシ樹脂を示す。 The epoxy resin is a bisphenol A type epoxy resin having a molecular weight of 45000 to 55000.
　硬化剤は、マイクロカプセル化したイミダゾール系潜在性硬化剤（旭化成イーマテリアルズ株式会社製、ノバキュア（登録商標）ＨＸ３９４１ＨＰ）を示す。 The curing agent indicates a microencapsulated imidazole-based latent curing agent (manufactured by Asahi Kasei E-Materials Co., Ltd., NovaCure (registered trademark) HX3941HP).
　各導電ペーストの粘度は、粘度計（東機産業株式会社製、ＴＶＥ-２２ＨＴ）により、温度２５℃±０．２℃で、コーンロータ（東機産業株式会社製、３°×Ｒ７．7（ロータコード０７））を用いて測定した。 The viscosity of each conductive paste was measured using a viscometer (manufactured by Toki Sangyo Co., Ltd., TVE-22HT) at a temperature of 25 ° C. ± 0.2 ° C. and a cone rotor (manufactured by Toki Sangyo Co., Ltd., 3 ° × R7.7 ( Measurement was performed using a rotor cord 07)).
　なお、表１に示す「η１」は、コーンロータの回転速度を１ｒｐｍ（せん断速度Ｄ１＝２ｓ－１）に設定し、回転開始から５分経過後の粘度を示す。 “Η1” shown in Table 1 indicates the viscosity after 5 minutes from the start of rotation with the rotation speed of the cone rotor set to 1 rpm (shear speed D1 = 2s −1 ).
　表１に示す「η２」は、コーンロータの回転速度を１０ｒｐｍ（せん断速度Ｄ２＝２０ｓ－１）に設定し、回転開始から３４秒経過後の粘度を示す。 “Η2” shown in Table 1 indicates the viscosity after 34 seconds from the start of rotation with the cone rotor rotation speed set to 10 rpm (shear speed D2 = 20 s −1 ).
Figure JPOXMLDOC01-appb-T000001
  
　表１に示すように導電ペースト１～３は上記（１）式（チクソトロピー指数が０．２５以下）を充たす。これは、扁平球状の導電粒子（第１導電粒子および第２導電粒子）の質量比を７０質量％以上に設定し、かつ第１導電粒子の質量比を第２導電粒子の質量比よりも小さくなるように導電ペーストを調製したことによる。一方、表１に示すように導電ペースト４，５は上記（１）式（チクソトロピー指数が０．２５以下）を充たさない。これは、扁平球状の第１導電粒子の質量比率を大きくし過ぎたことによる。
Figure JPOXMLDOC01-appb-T000001
As shown in Table 1, the conductive pastes 1 to 3 satisfy the above formula (1) (thixotropic index is 0.25 or less). This is because the mass ratio of the flat spherical conductive particles (first conductive particles and second conductive particles) is set to 70% by mass or more, and the mass ratio of the first conductive particles is smaller than the mass ratio of the second conductive particles. This is because the conductive paste was prepared. On the other hand, as shown in Table 1, the conductive pastes 4 and 5 do not satisfy the above formula (1) (thixotropic index is 0.25 or less). This is because the mass ratio of the flat spherical first conductive particles is excessively increased.
　実施例の導電ペーストでは、第１導電粒子として平均粒径１．９μｍの扁平球状の導電粒子を用い、かつ第２導電粒子として平均粒径０．９μｍの扁平球状の導電粒子を用いて、上記（１）式を充たす導電ペーストを実現する。一方、第２導電粒子として平均粒径０．５μｍ未満の扁平球状の導電粒子を主成分として用いて上記（１）式の導電ペーストを実現することは難しい。また、平均粒径３．３μｍよりも大きい扁平球状の導電粒子を主成分として用いて上記（１）式の導電ペーストを実現することは難しい。 In the conductive paste of the example, the first conductive particles are flat spherical conductive particles having an average particle diameter of 1.9 μm, and the second conductive particles are flat spherical conductive particles having an average particle diameter of 0.9 μm. (1) A conductive paste satisfying the equation is realized. On the other hand, it is difficult to realize the conductive paste of the above formula (1) using, as the main component, flat spherical conductive particles having an average particle size of less than 0.5 μm as the second conductive particles. In addition, it is difficult to realize the conductive paste of the above formula (1) using flat spherical conductive particles larger than the average particle size of 3.3 μm as a main component.
　すなわち、平均粒径が０．５μｍ以上３．３μｍ以下の範囲内にある扁平球状の導電粒子であれば、当該導電粒子の質量比を７０質量％以上に設定し、かつ第１導電粒子の質量比を第２導電粒子の質量比よりも小さくし、かつ溶剤の質量比等を適宜調整することにより、上記（１）式を充たす導電ペーストを形成することができる。 That is, in the case of flat spherical conductive particles having an average particle size in the range of 0.5 μm or more and 3.3 μm or less, the mass ratio of the conductive particles is set to 70% by mass or more and the mass of the first conductive particles is set. By making the ratio smaller than the mass ratio of the second conductive particles and appropriately adjusting the mass ratio of the solvent and the like, a conductive paste satisfying the above formula (1) can be formed.
　導電ペースト４は、上記（１）式に規定された範囲から僅かに外れるものであるが、この導電ペースト４を用いることにより、以降の実施例４に示すように、本実施形態の窪み４４の有するブラインドビア５０を形成することができる。しかし、ブラインドビア５０の窪み４４の深さは小さい。
実施例
　フレキシブルプリント配線板１の実施例について説明する。 The conductive paste 4 is slightly deviated from the range defined in the above formula (1). By using this conductive paste 4, as shown in Example 4 below, the depression 44 of the present embodiment A blind via 50 can be formed. However, the depth of the recess 44 of the blind via 50 is small.
Example An example of the flexible printed wiring board 1 will be described.
　各実施例のフレキシブルプリント配線板１は、ブラインドビア５０の構造を除き、同じ構造を有する。 The flexible printed wiring board 1 of each embodiment has the same structure except for the structure of the blind via 50.
　図６（ａ），（ｂ）に、各実施例に係るフレキシブルプリント配線板１を示す。 FIGS. 6A and 6B show the flexible printed wiring board 1 according to each embodiment.
　図６（ａ）はフレキシブルプリント配線板１の平面図であり、図６（ｂ）はフレキシブルプリント配線板１の断面図である。フレキシブルプリント配線板１は、デイジーチェーン状に連結した３６個のブラインドビア５０を有する。各第１ランド部１１は、基材３０の第１面３１に形成されている。各第２ランド部２１は、基材３０の第２面３２に形成されている。 6A is a plan view of the flexible printed wiring board 1, and FIG. 6B is a cross-sectional view of the flexible printed wiring board 1. FIG. The flexible printed wiring board 1 has 36 blind vias 50 connected in a daisy chain shape. Each first land portion 11 is formed on the first surface 31 of the base material 30. Each second land portion 21 is formed on the second surface 32 of the base material 30.
　第１ランド部１１は端から順に２個ずつ連結パターン１２により接続されている。第２ランド部２１は端から順に２個ずつ連結パターン２２により接続されている。第２面３２の連結パターン１２は、基材３０を挟んで、第１面３１の連結パターン１２の無い部分の反対側に形成されている。すなわち、平面視において、第１面３１の連結パターン１２と第２面３２の連結パターン２２とは、交互に配置されている。 The first land portions 11 are connected by connecting patterns 12 in order of two from the end. Two second land portions 21 are connected by connecting patterns 22 in order from the end. The connection pattern 12 of the second surface 32 is formed on the opposite side of the portion of the first surface 31 where there is no connection pattern 12 with the base material 30 in between. That is, in the plan view, the connection pattern 12 on the first surface 31 and the connection pattern 22 on the second surface 32 are alternately arranged.
　各部材の寸法は次のとおりである（図２および図６参照）。 The dimensions of each member are as follows (see FIGS. 2 and 6).
　寸法ｔａ（基材３０の厚さ）は１２μｍ。 Dimension ta (thickness of substrate 30) is 12 μm.
　寸法ｔｂ（第１ランド部１１の厚さ）は１２μｍ。 Dimension tb (thickness of the first land portion 11) is 12 μm.
　寸法Ｄｃ（ビア孔３３の内径）は１００μｍ。 Dimension Dc (inner diameter of via hole 33) is 100 μm.
　第１ランド部１１の外径は５００μｍ。 The outer diameter of the first land portion 11 is 500 μm.
　第２ランド部２１の外径は５００μｍ。 The outer diameter of the second land portion 21 is 500 μm.
　寸法ＴＤ（寸法ｔａ＋寸法ｔｂ）は２４μｍ。 Dimension TD (dimension ta + dimension tb) is 24 μm.
　表２を参照して、各実施例の相違について説明する。各実施例では、導電ペーストを異ならせている。 Referring to Table 2, the differences between the embodiments will be described. In each embodiment, the conductive paste is different.
　表２の「寸法ｔａ」は基材３０の厚さを示す。「寸法ｔｂ」は、第１ランド部１１の厚さを示す。「寸法Ｄｃ」は、ビア孔３３の内径を示す。「寸法ＴＤ」は、寸法ｔａと寸法ｔｂの和を示す。「寸法ｔｄ」は、ビア孔３３の中心軸Ｃａ上における導電体４０の厚さを示す。「寸法ｔｅ」は、導電体４０のうち第１ランド部１１を覆う部分（被覆部）の最も厚い箇所の厚さを示す。「寸法Ｄｆ」は、ビア孔３３の中心軸Ｃａに対し垂直でありかつ第１ランド部１１の表面１１ａを含む面に沿って、導電体４０を切断したときの導電体４０の断面において、この断面の内円と外円（ビア孔３３）との間の距離で最も小さい部分の距離を示す。「寸法Ｄｇ」は、導電体４０において、ビア孔３３の内側周面３３ａと第１ランド部１１を覆う部分（被覆部）の外周との間のうち、その間隔が最も小さい部分の距離を示す。これらの寸法ｔａ、ｔｂ、Ｄｃ、ｔｄ、ｔｅ、Ｄｆ、Ｄｇは、フレキシブルプリント配線板１の３６個のブラインドビア５０の平均値を示す。 “Dimension ta” in Table 2 indicates the thickness of the base material 30. “Dimension tb” indicates the thickness of the first land portion 11. “Dimension Dc” indicates the inner diameter of the via hole 33. “Dimension TD” indicates the sum of the dimension ta and the dimension tb. “Dimension td” indicates the thickness of the conductor 40 on the central axis Ca of the via hole 33. “Dimension te” indicates the thickness of the thickest portion of the conductor 40 that covers the first land portion 11 (covering portion). The “dimension Df” is a cross section of the conductor 40 when the conductor 40 is cut along a plane that is perpendicular to the central axis Ca of the via hole 33 and includes the surface 11a of the first land portion 11. The distance of the smallest part in the distance between the inner circle and outer circle (via hole 33) of a cross section is shown. “Dimension Dg” indicates the distance of the portion of the conductor 40 having the smallest interval between the inner peripheral surface 33a of the via hole 33 and the outer periphery of the portion covering the first land portion 11 (covering portion). . These dimensions ta, tb, Dc, td, te, Df, and Dg indicate the average values of the 36 blind vias 50 of the flexible printed wiring board 1.
　実施例１では、表１に示す導電ペースト１を用いて、フレキシブルプリント配線板１を形成した。 In Example 1, the flexible printed wiring board 1 was formed using the conductive paste 1 shown in Table 1.
　ブラインドビア５０の形状は次のとおりである（表２参照）。 The shape of the blind via 50 is as follows (see Table 2).
　ビア孔３３の中心軸Ｃａ上に窪み４４が形成された。 A depression 44 was formed on the central axis Ca of the via hole 33.
　導電体４０の厚さｔｄは、５μｍ以上であり、かつ寸法ｔａと寸法ｔｂとの和（寸法ＴＤ＝２４μｍ）未満であった。 The thickness td of the conductor 40 was 5 μm or more and less than the sum of the dimension ta and the dimension tb (dimension TD = 24 μm).
　導電体４０の被覆部の厚さｔｅは、２μｍ以上であった。 The thickness te of the covering portion of the conductor 40 was 2 μm or more.
　導電体４０の距離Ｄｆは、５μｍ以上であった。 The distance Df of the conductor 40 was 5 μm or more.
　導電体４０の被覆部の距離Ｄｇは、５μｍ以上であった。 The distance Dg of the covering portion of the conductor 40 was 5 μm or more.
　曲げ試験前後における電気的特性および外形上の変化は次のとおりである。 Changes in electrical characteristics and external shape before and after the bending test are as follows.
　曲げ試験前後のブラインドビア５０の抵抗増加率は、０．６％であった。この値は、判定値（１０％）よりも小さい。 The resistance increase rate of the blind via 50 before and after the bending test was 0.6%. This value is smaller than the determination value (10%).
　曲げ試験後において導電体４０と第１ランド部１１との間に剥離は確認されなかった。 No peeling was observed between the conductor 40 and the first land portion 11 after the bending test.
Figure JPOXMLDOC01-appb-T000002
 　図７を参照して、曲げ試験方法について説明する。
Figure JPOXMLDOC01-appb-T000002
 The bending test method will be described with reference to FIG.
　先端に半径ｒが１．０ｍｍの曲面を有する真鍮製の曲げ治具７０を準備する。曲げ試験の前に、導電パターンの抵抗を測定する。次に曲げ試験を行う。 A brass bending jig 70 having a curved surface with a radius r of 1.0 mm at the tip is prepared. Prior to the bending test, the resistance of the conductive pattern is measured. Next, a bending test is performed.
　試験に係るフレキシブルプリント配線板１の第１面３１を外側に配置し、かつフレキシブルプリント配線板１を曲げ治具７０に密着させて、曲げ治具７０の第１面７１から第２面７２まで曲面を通過するように、フレキシブルプリント配線板１を移動させる。次に、そのフレキシブルプリント配線板１の第２面３２を外側にし、かつフレキシブルプリント配線板１を曲げ治具７０に密着させて、曲げ治具７０の第１面７１から第２面７２まで曲面を通過するように移動させる。このような曲げ操作を１回とカウントし、合計で１０回の曲げ操作を行う。 From the first surface 71 to the second surface 72 of the bending jig 70, the first surface 31 of the flexible printed wiring board 1 according to the test is disposed outside and the flexible printed wiring board 1 is brought into close contact with the bending jig 70. The flexible printed wiring board 1 is moved so as to pass through the curved surface. Next, the second surface 32 of the flexible printed wiring board 1 is set to the outside, and the flexible printed wiring board 1 is brought into close contact with the bending jig 70 so as to be curved from the first surface 71 to the second surface 72 of the bending jig 70. Move to pass. Such a bending operation is counted as one time, and a total of 10 bending operations are performed.
　導電パターンの抵抗の測定は以下のように行う。 Measure the resistance of the conductive pattern as follows.
　曲げ試験の試験前と試験後とにおける導電パターンの抵抗に基づいて、抵抗変化率を求める。抵抗変化率は、３６個のブラインドビア５０の抵抗変化率の平均値として求められる。 The resistance change rate is obtained based on the resistance of the conductive pattern before and after the bending test. The resistance change rate is obtained as an average value of the resistance change rates of the 36 blind vias 50.
　実施例２では、表１に示す導電ペースト２を用いて、実施例１と同様の構造を有するフレキシブルプリント配線板１を形成した。 In Example 2, a flexible printed wiring board 1 having the same structure as Example 1 was formed using the conductive paste 2 shown in Table 1.
　実施例１と同様に、ビア孔３３の中心軸Ｃａ上に窪み４４が形成された。 As in Example 1, a depression 44 was formed on the central axis Ca of the via hole 33.
　また、導電体４０の厚さｔｄ（寸法ｔｄ）は、５μｍ以上であり、かつ寸法ｔａと寸法ｔｂとの和（寸法ＴＤ＝２４μｍ）未満であった。導電体４０の被覆部の厚さｔｅ（寸法ｔｅ）は、２μｍ以上であった。導電体４０の距離Ｄｆ（寸法Ｄｆ）は、５μｍ以上であった。導電体４０の被覆部の距離Ｄｇ（寸法Ｄｇ）は５μｍ以上であった。 The thickness td (dimension td) of the conductor 40 was 5 μm or more and less than the sum of the dimension ta and the dimension tb (dimension TD = 24 μm). The thickness te (dimension te) of the covering portion of the conductor 40 was 2 μm or more. The distance Df (dimension Df) of the conductor 40 was 5 μm or more. The distance Dg (dimension Dg) of the covering portion of the conductor 40 was 5 μm or more.
　曲げ試験前後のブラインドビア５０の抵抗の変化率は、１．４％であった。この値は、判定値（１０％）よりも小さい。曲げ試験後において導電体４０と第１ランド部１１との間に剥離は確認されなかった。すなわち、実施例１と同様の結果が得られた。 The change rate of the resistance of the blind via 50 before and after the bending test was 1.4%. This value is smaller than the determination value (10%). No peeling was observed between the conductor 40 and the first land portion 11 after the bending test. That is, the same result as in Example 1 was obtained.
　実施例３では、表１に示す導電ペースト３を用いて、実施例１と同様の構造を有するフレキシブルプリント配線板１を形成した。 In Example 3, a flexible printed wiring board 1 having the same structure as Example 1 was formed using the conductive paste 3 shown in Table 1.
　実施例１と同様に、ビア孔３３の中心軸Ｃａ上に窪み４４が形成された。導電体４０の厚さｔｄ（寸法ｔｄ）は、５μｍ以上であり、かつ寸法ｔａと寸法ｔｂとの和（寸法ＴＤ＝２４μｍ）未満であった。導電体４０の被覆部の厚さｔｅ（寸法ｔｅ）は、２μｍ以上であった。導電体４０の距離Ｄｆ（寸法Ｄｆ）は、５μｍ以上であった。導電体４０の被覆部の距離Ｄｇ（寸法Ｄｇ）は５μｍ以上であった。 As in Example 1, a depression 44 was formed on the central axis Ca of the via hole 33. The thickness td (dimension td) of the conductor 40 was 5 μm or more and less than the sum of the dimension ta and the dimension tb (dimension TD = 24 μm). The thickness te (dimension te) of the covering portion of the conductor 40 was 2 μm or more. The distance Df (dimension Df) of the conductor 40 was 5 μm or more. The distance Dg (dimension Dg) of the covering portion of the conductor 40 was 5 μm or more.
　曲げ試験前後のブラインドビア５０の抵抗の変化率は、２．１％であった。この値は、判定値（１０％）よりも小さい。曲げ試験後において導電体４０と第１ランド部１１との間に剥離は確認されなかった。すなわち、実施例１と同様の結果が得られた。 The change rate of the resistance of the blind via 50 before and after the bending test was 2.1%. This value is smaller than the determination value (10%). No peeling was observed between the conductor 40 and the first land portion 11 after the bending test. That is, the same result as in Example 1 was obtained.
　実施例４では、表１に示す導電ペースト４を用いて、実施例１と同様の構造を有するフレキシブルプリント配線板１を形成した。 In Example 4, the flexible printed wiring board 1 having the same structure as that of Example 1 was formed using the conductive paste 4 shown in Table 1.
　実施例１と同様に、ビア孔３３の中心軸Ｃａ上に窪み４４が形成された。また、導電体４０の厚さｔｄ（寸法ｔｄ）は、５μｍ以上であり、かつ寸法ｔａと寸法ｔｂとの和（寸法ＴＤ＝２４μｍ）未満であった。導電体４０の被覆部の厚さｔｅ（寸法ｔｅ）は、２μｍ以上であった。導電体４０の距離Ｄｆ（寸法Ｄｆ）は、５μｍ以上であった。導電体４０の被覆部の距離Ｄｇ（寸法Ｄｇ）は５μｍ以上であった。 As in Example 1, a depression 44 was formed on the central axis Ca of the via hole 33. Further, the thickness td (dimension td) of the conductor 40 was 5 μm or more and less than the sum of the dimension ta and the dimension tb (dimension TD = 24 μm). The thickness te (dimension te) of the covering portion of the conductor 40 was 2 μm or more. The distance Df (dimension Df) of the conductor 40 was 5 μm or more. The distance Dg (dimension Dg) of the covering portion of the conductor 40 was 5 μm or more.
　曲げ試験前後のブラインドビア５０の抵抗の変化率は、３．５％であった。この値は、判定値（１０％）よりも小さい。曲げ試験後において導電体４０と第１ランド部１１との間に剥離は確認されなかった。すなわち、実施例１と同様の結果が得られた。
比較例
　比較例では、表１に示す導電ペースト５を用いて、実施例１と同様の構造を有するフレキシブルプリント配線板１を形成した。 The rate of change in the resistance of the blind via 50 before and after the bending test was 3.5%. This value is smaller than the determination value (10%). No peeling was observed between the conductor 40 and the first land portion 11 after the bending test. That is, the same result as in Example 1 was obtained.
Comparative Example In the comparative example, a flexible printed wiring board 1 having the same structure as that of Example 1 was formed using the conductive paste 5 shown in Table 1.
　この場合、導電体４０にはビア孔３３に窪み４４が形成されなかった。曲げ試験前後のブラインドビア５０の抵抗の変化率は、１８．２％であった。この値は、判定値（１０％）よりも大きい。曲げ試験後において導電体４０と第１ランド部１１との間に剥離が発生した。 In this case, the recess 44 was not formed in the via hole 33 in the conductor 40. The rate of change in the resistance of the blind via 50 before and after the bending test was 18.2%. This value is larger than the determination value (10%). Separation occurred between the conductor 40 and the first land portion 11 after the bending test.
　以上の結果から次のことが示される。 The above results indicate the following.
　導電体４０においてビア孔３３の中心軸Ｃａ上に窪み４４が存在し、かつ導電体４０の厚さｔｄ（寸法ｔｄ）が寸法ｔａと寸法ｔｂとの和（寸法ＴＤ）未満である場合には、従来構造のブラインドビア３５０に比べて、フレキシブルプリント配線板１の曲げに対するブラインドビア５０の接触抵抗の増分が少なくなる。これは、主に、窪み４４の存在によるブラインドビア５０の曲げ弾性率の低下に起因する。 In the conductor 40, when the depression 44 exists on the central axis Ca of the via hole 33 and the thickness td (dimension td) of the conductor 40 is less than the sum of the dimension ta and the dimension tb (dimension TD). As compared with the blind via 350 having the conventional structure, the increment of the contact resistance of the blind via 50 with respect to the bending of the flexible printed wiring board 1 is reduced. This is mainly due to a decrease in the flexural modulus of the blind via 50 due to the presence of the recess 44.
　このような窪み４４を有するブラインドビア３５０を形成するためには、チクソトロピー指数が０．２５以下の導電ペーストを用いることがより好ましいことが示される。実施例４では、チクソトロピー指数が０．２８の導電ペーストを用いることにより、窪み４４を有しかつ試験後の抵抗増加率が１０％以下のブラインドビア３５０を形成しているが、その窪み４４の深さは小さい。このため、窪み４４を確実に形成するためには、導電ペーストのチクソトロピー指数を０．２５以下にすることが好ましいといえる。 It is shown that it is more preferable to use a conductive paste having a thixotropy index of 0.25 or less in order to form the blind via 350 having such a depression 44. In Example 4, the conductive paste having a thixotropy index of 0.28 is used to form the blind via 350 having the depression 44 and having a resistance increase rate of 10% or less after the test. The depth is small. For this reason, in order to form the hollow 44 reliably, it can be said that it is preferable to make the thixotropy index | exponent of an electrically conductive paste into 0.25 or less.
　導電ペーストのチクソトロピー指数を０．２５以下にするためには、第１導電粒子（平均粒径が１．４μｍ以上３．３μｍ以下の導電粒子）の質量比を第２導電粒子（平均粒径が０．５μｍ以上１．８μｍ以下の導電粒子）の質量比よりも小さくすることが好ましい。すなわち、実施例４では、第１導電粒子の質量比が第２導電粒子の質量比よりも大きい導電ペースト４を用いている。そして、この導電ペースト４でも、窪み４４を有しかつ試験後の抵抗増加率が１０％以下のブラインドビア３５０を形成することができる。しかし、その窪み４４の深さは小さい。このため、窪み４４を確実に形成するためには、第１導電粒子の質量比が第２導電粒子の質量比よりも小さい導電ペーストを用いることが好ましい。 In order to set the thixotropy index of the conductive paste to 0.25 or less, the mass ratio of the first conductive particles (conductive particles having an average particle size of 1.4 μm to 3.3 μm) is set to the second conductive particles (average particle size is The mass ratio of the conductive particles (0.5 μm to 1.8 μm) is preferably smaller. That is, in Example 4, the conductive paste 4 in which the mass ratio of the first conductive particles is larger than the mass ratio of the second conductive particles is used. And also with this electrically conductive paste 4, the blind via | veer 350 which has the hollow 44 and whose resistance increase rate after a test is 10% or less can be formed. However, the depth of the depression 44 is small. For this reason, in order to reliably form the depression 44, it is preferable to use a conductive paste in which the mass ratio of the first conductive particles is smaller than the mass ratio of the second conductive particles.
　本実施形態の効果を説明する。 The effect of this embodiment will be described.
　（１）本実施形態では、ビア孔３３の中心軸Ｃａ上における導電体４０の厚さ（寸法ｔｄ）を、基材３０の厚さ（寸法ｔａ）と第１ランド部１１の厚さ（寸法ｔｂ）との和（寸法ＴＤ）よりも小さくしている。 (1) In this embodiment, the thickness (dimension td) of the conductor 40 on the central axis Ca of the via hole 33 is the same as the thickness (dimension ta) of the substrate 30 and the thickness (dimension) of the first land portion 11. It is smaller than the sum (dimension TD) with tb).
　フレキシブルプリント配線板１を曲げるとき、基材３０の外面が延びるとともに内面が縮む。このとき、第１ランド部１１と導電体４０とが離間する方向に力が加わる。この結果、導電体４０と第１ランド部１１との間に隙間が生じ、ブラインドビア５０の接触抵抗が増大する。 When the flexible printed wiring board 1 is bent, the outer surface of the substrate 30 extends and the inner surface shrinks. At this time, force is applied in a direction in which the first land portion 11 and the conductor 40 are separated from each other. As a result, a gap is generated between the conductor 40 and the first land portion 11, and the contact resistance of the blind via 50 is increased.
　ブラインドビア５０の接触抵抗の増大の程度は、ブラインドビア５０を構成する導電体４０の構造に依存する。フレキシブルプリント配線板１の曲げに際し、導電体４０が変形しない場合、ビア孔３３の内側周面３３ａと導電体４０とが離間し、または、第１ランド部１１から導電体４０が剥離する。このため、ブラインドビア５０の接触抵抗が増大する。 The degree of increase in the contact resistance of the blind via 50 depends on the structure of the conductor 40 constituting the blind via 50. When the conductor 40 is not deformed when the flexible printed wiring board 1 is bent, the inner peripheral surface 33a of the via hole 33 and the conductor 40 are separated from each other, or the conductor 40 is peeled from the first land portion 11. For this reason, the contact resistance of the blind via 50 increases.
　一方、フレキシブルプリント配線板１の曲げに際し、その曲げに応じて導電体４０が変形する場合には、ビア孔３３の内側周面３３ａと導電体４０とが離間せず、また、第１ランド部１１から導電体４０は剥離しない。このため、ブラインドビア５０の接触抵抗の増大は小さい。 On the other hand, when the conductor 40 is deformed in accordance with the bending of the flexible printed wiring board 1, the inner peripheral surface 33 a of the via hole 33 and the conductor 40 are not separated from each other, and the first land portion The conductor 40 does not peel from 11. For this reason, the increase in the contact resistance of the blind via 50 is small.
　本実施形態では、このような点を考慮し、上記したように、ビア孔３３の中心軸Ｃａ上における導電体４０の厚さ（寸法ｔｄ）を、基材３０の厚さ（寸法ｔａ）と第１ランド部１１の厚さ（寸法ｔｂ）との和よりも小さくする。すなわち、導電体４０において、ビア孔３３の中心軸Ｃａ上に窪み４４を設け、導電体４０が変形しやすい形状とし、基材３０の変形に追従して導電体４０が変形しやすい構造とする。これにより、フレキシブルプリント配線板１の曲げに対するブラインドビア５０の接触抵抗の増大を抑制することができる。 In the present embodiment, in consideration of such points, as described above, the thickness (dimension td) of the conductor 40 on the central axis Ca of the via hole 33 is set to the thickness (dimension ta) of the substrate 30. It is smaller than the sum of the thickness (dimension tb) of the first land portion 11. That is, in the conductor 40, a recess 44 is provided on the central axis Ca of the via hole 33 so that the conductor 40 is easily deformed, and the conductor 40 is easily deformed following the deformation of the substrate 30. . Thereby, the increase in the contact resistance of the blind via 50 with respect to the bending of the flexible printed wiring board 1 can be suppressed.
　（２）本実施形態では、ビア孔３３の中心軸Ｃａ上における導電体４０の厚さ（寸法ｔｄ）を５μｍ以上としている。 (2) In this embodiment, the thickness (dimension td) of the conductor 40 on the central axis Ca of the via hole 33 is 5 μm or more.
　フレキシブルプリント配線板１を曲げると導電体４０が変形する。導電体４０が薄いとき、導電体４０に亀裂が生じる可能性が高くなる。導電体４０において、ビア孔３３の中心軸Ｃａ上の厚さｔｄを５μｍ未満とすると、導電体４０に亀裂が生じる可能性が増大する。そこで、導電体４０の厚さｔｄを５μｍ以上とする。これにより、ビア孔３３の中心軸Ｃａ上の導電体４０の厚さｔｄを５μｍ未満とする場合に比べ、導電体４０に亀裂が発生することを抑制することができる。 When the flexible printed wiring board 1 is bent, the conductor 40 is deformed. When the conductor 40 is thin, there is a high possibility that the conductor 40 will crack. In the conductor 40, if the thickness td on the central axis Ca of the via hole 33 is less than 5 μm, the possibility that the conductor 40 will crack increases. Therefore, the thickness td of the conductor 40 is set to 5 μm or more. Thereby, compared with the case where the thickness td of the conductor 40 on the central axis Ca of the via hole 33 is less than 5 μm, the occurrence of cracks in the conductor 40 can be suppressed.
　（３）本実施形態では、導電体４０のうち第１ランド部１１を覆う部分の最も厚いところの厚さ（寸法ｔｅ）を２μｍ以上としている。 (3) In the present embodiment, the thickness (dimension te) of the thickest portion of the conductor 40 covering the first land portion 11 is set to 2 μm or more.
　導電体４０において第１ランド部１１を覆う部分は、導電体４０と第１ランド部１１との間の接触抵抗の大きさに関係する。第１ランド部１１を覆う部分に亀裂が生じるとき、導電体４０と第１ランド部１１との間の接触抵抗が増大する。この点を考慮し、第１ランド部１１を覆う部分の最も厚いところの厚さｔｅを２μｍ以上に設定する。これにより、第１ランド部１１を覆う部分に亀裂が発生することを抑制することができる。 The portion of the conductor 40 that covers the first land portion 11 is related to the magnitude of the contact resistance between the conductor 40 and the first land portion 11. When a crack occurs in the portion covering the first land portion 11, the contact resistance between the conductor 40 and the first land portion 11 increases. Considering this point, the thickness te of the thickest portion covering the first land portion 11 is set to 2 μm or more. Thereby, it can suppress that a crack generate | occur | produces in the part which covers the 1st land part 11. FIG.
　（４）本実施形態では距離Ｄｆ（寸法Ｄｆ）を５μｍ以上としている。 (4) In this embodiment, the distance Df (dimension Df) is 5 μm or more.
　導電体４０においてビア孔３３の開口部３４に対応する部分は、亀裂が生じやすい。そこで、ビア孔３３の中心軸Ｃａに対して垂直でありかつ第１ランド部１１の表面１１ａを含む面で導電体４０を切断したときのドーナツ状の断面において、導電体４０の断面の内円と外円（ビア孔３３の内側周面３３ａに対応する円）との間の距離Ｄｆ（寸法Ｄｆ）を５μｍ以上とする。これにより、ビア孔３３の第１ランド部１１側の開口部３４に対応する部分において、亀裂が発生することを抑制することができる。 A portion of the conductor 40 corresponding to the opening 34 of the via hole 33 is likely to crack. Therefore, in the donut-shaped cross section when the conductor 40 is cut by a plane perpendicular to the central axis Ca of the via hole 33 and including the surface 11a of the first land portion 11, an inner circle of the cross section of the conductor 40 is obtained. The distance Df (dimension Df) between the outer circle and the outer circle (a circle corresponding to the inner peripheral surface 33a of the via hole 33) is 5 μm or more. Thereby, it can suppress that a crack generate | occur | produces in the part corresponding to the opening part 34 by the side of the 1st land part 11 of the via hole 33. FIG.
　（５）本実施形態では距離Ｄｇ（寸法Ｄｇ）を５μｍ以上としている。 (5) In this embodiment, the distance Dg (dimension Dg) is 5 μm or more.
　導電体４０のうち第１ランド部１１を覆う被覆部において、ビア孔３３の内側周面３３ａと第１ランド部１１を覆う被覆部の外周との間のうち、その間隔が最も小さいところの距離Ｄｇを小さくするとき、剥離が発生しやすくなる。そこで、この距離Ｄｇ（寸法Ｄｇ）を５μｍ以上とする。これにより、導電体４０の被覆部において亀裂が発生することを抑制することができる。 In the covering portion covering the first land portion 11 of the conductor 40, the distance between the inner peripheral surface 33a of the via hole 33 and the outer periphery of the covering portion covering the first land portion 11 is the smallest distance. When Dg is reduced, peeling tends to occur. Therefore, the distance Dg (dimension Dg) is set to 5 μm or more. Thereby, it can suppress that a crack generate | occur | produces in the coating | coated part of the conductor 40. FIG.
　（６）本実施形態では、導電体４０を、扁平球状の導電粒子６０およびこれらの結合体を含む構造としている。 (6) In the present embodiment, the conductor 40 has a structure including flat spherical conductive particles 60 and a combination thereof.
　導電体４０を構成する導電粒子６０の表面に突起があるとき、隣接する導電粒子６０の間の隙間が多くなる。そこで、導電体４０を扁平球状の導電粒子６０により構成し、導電粒子６０の密度を大きくする。これにより、ブラインドビア５０の許容電流量を高くすることができる。 When there are protrusions on the surface of the conductive particles 60 constituting the conductor 40, the gap between the adjacent conductive particles 60 increases. Therefore, the conductor 40 is composed of flat spherical conductive particles 60, and the density of the conductive particles 60 is increased. Thereby, the allowable current amount of the blind via 50 can be increased.
　（７）本実施形態に係るフレキシブルプリント配線板１の製造方法では、上記（１）式に示すように、チクソトロピー指数が０．２５以下の導電ペーストを用いる。従来の導電ペーストによれば、導電体４０の上部４１は表面張力により盛り上がる。 (7) In the method for manufacturing the flexible printed wiring board 1 according to the present embodiment, a conductive paste having a thixotropy index of 0.25 or less is used as shown in the above formula (1). According to the conventional conductive paste, the upper portion 41 of the conductor 40 rises due to surface tension.
　一方、本実施形態の導電ペーストによれば、導電体４０の上部４１の中央部分を窪ませることができる。これは次の理由による。 On the other hand, according to the conductive paste of the present embodiment, the central portion of the upper portion 41 of the conductor 40 can be recessed. This is due to the following reason.
　従来の製造方法では、チクソトロピー指数が大きい導電ペースト、すなわち、せん断応力を加えない状態において粘度が増大する導電ペーストが用いられていた。このため、導電ペーストをビア孔３３に充填した後、導電ペーストが広がらず、盛り上がった状態となっていた。 In the conventional manufacturing method, a conductive paste having a large thixotropy index, that is, a conductive paste having an increased viscosity when no shear stress is applied, has been used. For this reason, after filling the via hole 33 with the conductive paste, the conductive paste did not spread and was in a raised state.
　一方、本実施形態の製造方法では、チクソトロピー指数が０．２５以下の導電ペーストを用いる。これにより、導電ペーストを基材３０に塗布した後に導電ペーストを流動させることができる。この結果、導電ペーストは、ビア孔３３の形状に沿うように流動し、導電体４０の中央部分が窪む。すなわち、チクソトロピー指数が０．２５以下の導電ペーストを用いることにより、導電体４０の中央部分に窪み４４を形成することができる。 On the other hand, in the manufacturing method of the present embodiment, a conductive paste having a thixotropy index of 0.25 or less is used. Thereby, after apply | coating the electrically conductive paste to the base material 30, an electrically conductive paste can be made to flow. As a result, the conductive paste flows along the shape of the via hole 33, and the central portion of the conductor 40 is depressed. That is, the depression 44 can be formed in the central portion of the conductor 40 by using a conductive paste having a thixotropy index of 0.25 or less.
　（８）本実施形態では、チクソトロピー指数が０．２５以下であり、扁平球状の導電粒子を含み、これら扁平球状の導電粒子の導電ペースト全体に対する質量比が７０質量％以上である導電ペーストを用いる。これにより、導電体４０の表面４３の中央部分を窪ませることができる。 (8) In the present embodiment, a conductive paste having a thixotropy index of 0.25 or less, including flat spherical conductive particles, and a mass ratio of these flat spherical conductive particles to the entire conductive paste is 70% by mass or more is used. . Thereby, the central part of the surface 43 of the conductor 40 can be depressed.
　（９）本実施形態では、次の導電ペーストを用いることもできる。 (9) In the present embodiment, the following conductive paste can also be used.
　導電ペーストに、平均粒径が０．５μｍ以上１．８μｍ以下でありかつ扁平球状の導電粒子（第２導電粒子）と、平均粒径が１．４μｍ以上３．３μｍ以下の導電粒子（第１導電粒子）とを含める。これにより、導電体４０の上部４１の中央部分を窪ませることができる。 The conductive paste has an average particle size of 0.5 μm or more and 1.8 μm or less and a flat spherical conductive particle (second conductive particle), and an average particle size of 1.4 μm or more and 3.3 μm or less of conductive particles (first Conductive particles). Thereby, the center part of the upper part 41 of the conductor 40 can be depressed.
　また、平均粒径が１．４μｍ以上３．３μｍ以下の導電粒子（第１導電粒子）を導電ペーストに含めることから、次の効果が得られる。すなわち、１．４μｍ以上３．３μｍ以下の導電粒子（第１導電粒子）は導電ペーストの膜厚を大きくする。これにより、導電ペーストが薄くなりすぎることを抑制することができる。 In addition, since conductive particles (first conductive particles) having an average particle size of 1.4 μm or more and 3.3 μm or less are included in the conductive paste, the following effects can be obtained. That is, the conductive particles (first conductive particles) having a size of 1.4 μm or more and 3.3 μm or less increase the thickness of the conductive paste. Thereby, it can suppress that an electrically conductive paste becomes thin too much.
　さらに、上記（９）の構成において、第１導電粒子の質量比を３０質量％以下にする個とが好ましい。第１導電粒子の質量比が大きいとき、窪み４４が形成されにくくなる。このため、第１導電粒子の質量比を３０質量％以下とすることにより、より確実に窪み４４が形成を形成することができる。 Furthermore, in the configuration of (9) above, it is preferable that the mass ratio of the first conductive particles is 30% by mass or less. When the mass ratio of the first conductive particles is large, the recess 44 is difficult to be formed. For this reason, the depression 44 can be more reliably formed by setting the mass ratio of the first conductive particles to 30 mass% or less.
　（１０）本実施形態では、次の導電ペーストを用いることもできる。 (10) In the present embodiment, the following conductive paste can also be used.
　導電ペーストに、平均粒径が３０ｎｍ以上２００ｎｍ以下の球状の導電粒子（第３導電粒子）を含め、更に、導電ペーストのチクソトロピー指数を０．２５以下とする。これにより、導電体４０の上部４１の中央部分を窪ませることができる。 The spherical conductive particles (third conductive particles) having an average particle size of 30 nm to 200 nm are included in the conductive paste, and the thixotropic index of the conductive paste is set to 0.25 or less. Thereby, the center part of the upper part 41 of the conductor 40 can be depressed.
　平均粒径が３０ｎｍ以上２００ｎｍ以下の球状の導電粒子（第３導電粒子）を導電ペーストに含めることから、次の効果が得られる。すなわち、これら導電粒子は、扁平球状の導電粒子（第１導電粒子および第２導電粒子）の間の隙間に入るため、このような導電ペーストにより形成される導電体４０では、導電粒子密度を高くできる。このため、ブラインドビア５０の最大許容電流量が高くなる。
その他の実施形態
　なお、本発明の実施態様は上記に示した態様に限られるものではなく、これを例えば、以下に示すように変更して実施することもできる。また、以下の各変形例は、上記各実施形態についてのみ適用されるものではなく、異なる変形例同士を互いに組み合わせて実施することもできる。 Since spherical conductive particles (third conductive particles) having an average particle size of 30 nm to 200 nm are included in the conductive paste, the following effects can be obtained. That is, since these conductive particles enter the gap between the flat spherical conductive particles (first conductive particles and second conductive particles), in the conductor 40 formed of such a conductive paste, the conductive particle density is increased. it can. For this reason, the maximum allowable current amount of the blind via 50 is increased.
Other Embodiments Note that the embodiments of the present invention are not limited to the above-described embodiments, and the embodiments can be modified as follows, for example. In addition, the following modifications are not applied only to the above-described embodiments, and different modifications can be performed in combination with each other.
　・上記実施形態では、導電体４０に窪み４４を形成する手段として、チクソトロピー指数が０．２５以上の導電ペーストを用いることを採用したが、窪み４４の形成手段は、これに限定されない。例えば、ビア孔３３に導電ペーストを充填した後、一次硬化した状態においてプレスすることにより、ビア孔３３の中心軸Ｃａ上に窪み４４を形成するという手段を採用することもできる。この場合、金型の選択により、窪み４４の深さ、形状等を任意に設定することができる。 In the above embodiment, as the means for forming the depression 44 in the conductor 40, the use of a conductive paste having a thixotropy index of 0.25 or more is adopted, but the means for forming the depression 44 is not limited to this. For example, after filling the via hole 33 with the conductive paste and pressing in the primary cured state, a means of forming the depression 44 on the central axis Ca of the via hole 33 can be adopted. In this case, the depth, shape, and the like of the recess 44 can be arbitrarily set by selecting a mold.
　・上記実施形態では、窪み４４のある導電体４０の構造をブラインドビア５０に適用しているが、本構造はブラインドビア５０にのみ適用されるものではない。例えば、ビア孔３３に相当する孔もしくは溝に導電ペーストを充填して導電体４０を形成するフレキシブルプリント配線板１において、当該導電体４０に対しても本発明を適用することができる。この場合においも、ビア孔３３に相当する孔もしくは溝と導電体４０との剥離を抑制することができる。 In the above embodiment, the structure of the conductor 40 having the depression 44 is applied to the blind via 50, but this structure is not applied only to the blind via 50. For example, in the flexible printed wiring board 1 in which the conductor 40 is formed by filling a hole or groove corresponding to the via hole 33 with the conductive paste, the present invention can also be applied to the conductor 40. Also in this case, peeling of the conductor 40 from the hole or groove corresponding to the via hole 33 can be suppressed.
　・上記実施形態では、両面導電層のフレキシブルプリント配線板１について本発明を適用した例を挙げたが、本発明は、３層以上の多層フレキシブルプリント配線板にも適用することができる。 In the above embodiment, the example in which the present invention is applied to the flexible printed wiring board 1 having a double-sided conductive layer has been described, but the present invention can also be applied to a multilayer flexible printed wiring board having three or more layers.
　１…フレキシブルプリント配線板、１０…第１導電パターン、１１…第１ランド部、１１ａ…表面、１１ｂ…ランド孔、１２…連結パターン、２０…第２導電パターン、２１…第２ランド部、２２…連結パターン、３０…基材、３１…第１面、３２…第２面、３３…ビア孔、３３ａ…内側周面、３３ｂ…底面、３４…開口部、４０…導電体、４１…上部、４２…底部、４３…表面、４４…窪み、５０…ブラインドビア、６０…導電粒子、７０…曲げ治具、７１…第１面、７２…第２面、１００…ブラインドビア、１１０…基材、１１１…第１ランド部、１１２…第２ランド部、１１３…ビア孔、１１４…導電体、１１５…表面、２００…ブラインドビア、２１０…導電体、２１１…表面、２１２…窪み、３００…フレキシブルプリント配線板、３１１…第１ランド部、３１１ａ…表面、３２１…第２ランド部、３３０…基材、３３３…ビア孔、３３３ａ…内側周面、３４０…導電体、３４１…上部、３５０…ブラインドビア。 DESCRIPTION OF SYMBOLS 1 ... Flexible printed wiring board, 10 ... 1st conductive pattern, 11 ... 1st land part, 11a ... Surface, 11b ... Land hole, 12 ... Connection pattern, 20 ... 2nd conductive pattern, 21 ... 2nd land part, 22 Connection pattern, 30 ... base material, 31 ... first surface, 32 ... second surface, 33 ... via hole, 33a ... inner peripheral surface, 33b ... bottom surface, 34 ... opening, 40 ... conductor, 41 ... upper part, 42 ... bottom, 43 ... surface, 44 ... depression, 50 ... blind via, 60 ... conductive particles, 70 ... bending jig, 71 ... first surface, 72 ... second surface, 100 ... blind via, 110 ... base material, DESCRIPTION OF SYMBOLS 111 ... 1st land part, 112 ... 2nd land part, 113 ... Via hole, 114 ... Conductor, 115 ... Surface, 200 ... Blind via, 210 ... Conductor, 211 ... Surface, 212 ... Depression, 300 ... Flexible print wiring , 311 ... first land portion, 311a ... surface, 321 ... second land portion, 330 ... substrate, 333 ... via hole, 333a ... inner peripheral surface, 340 ... conductor, 341 ... top 350 ... blind vias.

Claims (9)

  1. 　基材と、前記基材の第１面に形成された第１導電層と、前記基材の第２面に形成された第２導電層と、前記第１導電層と前記第２導電層とを接続する導電体とを備えるフレキシブルプリント配線板であって、
    　前記第１導電層に設けられた第１ランド部と、
    　前記第２導電層において前記基材を挟んで前記第１ランド部の反対側に設けられた第２ランド部と、
    　前記第１ランド部および前記基材を貫通して前記第２ランド部に達するビア孔とを備え、
    　前記導電体は、導電ペーストにより形成されたものであって、
    　前記導電体は、前記ビア孔の底面の全部を覆うようにこのビア孔を充たし、かつ前記第１ランド部の表面の少なくとも一部を覆うように形成され、
    　前記ビア孔の中心軸上における前記導電体の厚さは、前記基材の厚さと前記第１ランド部の厚さとの和よりも小さいことを含むフレキシブルプリント配線板。     A base material, a first conductive layer formed on the first surface of the base material, a second conductive layer formed on the second surface of the base material, the first conductive layer and the second conductive layer, A flexible printed wiring board comprising a conductor for connecting
    A first land portion provided in the first conductive layer;
    A second land portion provided on the opposite side of the first land portion across the base material in the second conductive layer;
    A via hole penetrating the first land portion and the base material to reach the second land portion,
    The conductor is formed of a conductive paste,
    The conductor is formed to fill the via hole so as to cover the entire bottom surface of the via hole, and to cover at least a part of the surface of the first land portion,
    The flexible printed wiring board including a thickness of the conductor on a central axis of the via hole being smaller than a sum of a thickness of the base material and a thickness of the first land portion.
  2. 　請求項１に記載のフレキシブルプリント配線板であって、前記ビア孔の中心軸上における前記導電体の厚さは５μｍ以上であるフレキシブルプリント配線板。 2. The flexible printed wiring board according to claim 1, wherein the thickness of the conductor on the central axis of the via hole is 5 μm or more.
  3. 　請求項１または２に記載のフレキシブルプリント配線板であって、前記導電体のうち、前記第１ランド部を覆う部分の最も厚い箇所の厚さが２μｍ以上であるフレキシブルプリント配線板。 3. The flexible printed wiring board according to claim 1, wherein the thickest portion of the conductor covering the first land portion has a thickness of 2 μm or more.
  4. 　請求項１～３のいずれか一項に記載のフレキシブルプリント配線板であって、前記ビア孔の中心軸に対し垂直であり、かつ、前記第１ランド部の表面を含む面に沿って、前記導電体を切断したときの前記導電体の断面において、この断面の内円と外円との間の距離は５μｍ以上であるフレキシブルプリント配線板。 The flexible printed wiring board according to any one of claims 1 to 3, wherein the flexible printed wiring board is perpendicular to a central axis of the via hole and extends along a surface including a surface of the first land portion. A flexible printed wiring board, wherein a distance between an inner circle and an outer circle of the conductor when the conductor is cut is 5 μm or more.
  5. 　請求項１～４のいずれか一項に記載のフレキシブルプリント配線板であって、前記導電体は、扁平球状の導電粒子およびこれらの結合体を含むフレキシブルプリント配線板。 The flexible printed wiring board according to any one of claims 1 to 4, wherein the conductor includes flat spherical conductive particles and a combination thereof.
  6. 　基材と、前記基材の第１面に形成された第１導電層と、前記基材の第２面に形成された第２導電層と、前記第１導電層と前記第２導電層とを接続する導電体とを備えるフレキシブルプリント配線板の製造方法であって、
    　（１）式で示されるチクソトロピー指数が０．２５以下の導電ペーストを用いて前記導電体を形成することを含むフレキシブルプリント配線板の製造方法。
    　チクソトロピー指数
    ＝ｌｏｇ（η１／η２）／ｌｏｇ（Ｄ２／Ｄ１）・・・（１）
    　ここで、η１はせん断速度Ｄ１が２ｓ－１のときの前記導電ペーストの粘度を示し、η２はせん断速度Ｄ２が２０ｓ－１のときの前記導電ペーストの粘度を示す。     A base material, a first conductive layer formed on the first surface of the base material, a second conductive layer formed on the second surface of the base material, the first conductive layer and the second conductive layer, A method for producing a flexible printed wiring board comprising a conductor for connecting
    (1) The manufacturing method of a flexible printed wiring board including forming the said conductor using the electrically conductive paste whose thixotropy index shown by Formula is 0.25 or less.
    Thixotropic index = log (η1 / η2) / log (D2 / D1) (1)
    Here, η1 indicates the viscosity of the conductive paste when the shear rate D1 is 2 s −1 , and η2 indicates the viscosity of the conductive paste when the shear rate D2 is 20 s −1 .
  7. 　請求項６に記載のフレキシブルプリント配線板の製造方法であって、扁平球状の導電粒子を含み、かつ、この扁平球状の導電粒子の導電ペースト全体に対する質量比が７０質量％以上である導電ペーストを用いて、前記導電体を形成することを含むフレキシブルプリント配線板の製造方法。 It is a manufacturing method of the flexible printed wiring board of Claim 6, Comprising: The electrically conductive paste which contains a flat spherical conductive particle and whose mass ratio with respect to the whole conductive paste of this flat spherical conductive particle is 70 mass% or more. A method for producing a flexible printed wiring board, comprising forming the conductor.
  8. 　請求項７に記載のフレキシブルプリント配線板の製造方法であって、前記導電ペーストは、平均粒径が３０ｎｍ以上２００ｎｍ以下の球状の導電粒子を更に含むフレキシブルプリント配線板の製造方法。 8. The method for manufacturing a flexible printed wiring board according to claim 7, wherein the conductive paste further includes spherical conductive particles having an average particle diameter of 30 nm to 200 nm.
  9. 　請求項７または８に記載のフレキシブルプリント配線板の製造方法であって、前記導電ペーストには、前記扁平球状の導電粒子として、平均粒径が１．４μｍ以上３．３μｍ以下の第１導電粒子と、平均粒径が０．５μｍ以上１．８μｍ以下の第２導電粒子とが含まれるフレキシブルプリント配線板の製造方法。 It is a manufacturing method of the flexible printed wiring board of Claim 7 or 8, Comprising: In the said electrically conductive paste, 1st electroconductive particle with an average particle diameter of 1.4 micrometers or more and 3.3 micrometers or less as said flat spherical electrically conductive particle. And a method for producing a flexible printed wiring board, which includes second conductive particles having an average particle size of 0.5 μm or more and 1.8 μm or less.
PCT/JP2013/065644 2012-06-08 2013-06-06 Flexible printed wiring board and method for producing flexible printed wiring board WO2013183692A1 (en)

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