JP2011029348A - Connection structure of printed wiring board and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a connection structure, or the like of a printed wiring board capable of easily obtaining fully high connection strength by electrically connecting a flying lead of one printed wiring board to conductor wiring (substrate pad) of the other printed wiring board. <P>SOLUTION: The connection structure 50 of a printed wiring board includes: a first printed wiring board 10 including a plurality of conductors 15 positioned on a base material 11; a second printed wiring board 20 including the plurality of flying leads 25; an anisotropic conductive adhesive 33 for connecting the conductor of the first printed wiring board to the flying leads of the second printed wiring board; and a protective film 31 positioned on the second printed wiring board. The pull strength of the protective film 31 is larger than that of PTFE. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a printed wiring board connection structure and a manufacturing method thereof, and more specifically, a printed wiring board connection structure suitable for a case where one of the wiring boards is connected to a flying lead in an electronic device or the like. And its manufacturing method.

  In electronic devices, a structure in which conductor wirings on two printed wiring boards are electrically connected is often used. In some types of electronic equipment, the flexible printed wiring board may be placed along the front, side, and back of mechanical parts in the electronic equipment. Often the front and back are reversed. For this reason, in order to increase the flexibility of parts in production, in the field of use where the front and back surfaces are reversed at both ends as described above, the insulating base material is excluded from the conductor wiring at the connection part of the flexible printed wiring board. Thus, a bare conductor wiring called a flying lead is formed. Since the flying lead is connected facing the other conductor wiring on the front side or the back side, it is not necessary to prepare a flexible printed wiring board for each number of times of folding and for each folding form. Such connection between the flying lead and the conductor of the mating printed wiring board is performed by ultrasonic bonding in particular (Patent Document 1). As a result, a connection structure having a large bonding strength can be easily obtained.

JP 2007-173362 A

However, if the amount of information processed by electronic equipment increases rapidly and the fine pitch of the conductors on the printed wiring board progresses, ultrasonic bonding cannot eliminate the possibility of short-circuiting, and a connection method that supports fine pitch Development is underway. For this reason, a method has been studied in which an anisotropic conductive film (ACF: Anisotropy Conductive Film) is used to easily connect the flying lead to a substrate pad of a printed wiring board to make an electrical connection. This method of electrically connecting the flying leads using the ACF can easily cope with the fine pitch of the conductor, but has a drawback that the connection strength is not sufficiently strong.
The present invention provides a printed wiring board connection that can easily obtain a sufficiently high connection strength while electrically connecting the flying lead of one printed wiring board and the conductor wiring (board pad) of the other printed wiring board. It is an object of the present invention to provide a structure and a manufacturing method thereof.

  The method for manufacturing a printed wiring board connection structure according to the present invention includes a step of preparing a first printed wiring board in which a plurality of conductors are positioned on a base material, and anisotropic conductive adhesion on the first printed wiring board. A step of arranging an agent film, a step of arranging a second printed wiring board having flying leads on the ACF in accordance with the first printed wiring board, and a resin film from above the second printed wiring board And a step of thermocompression-bonding by applying pressure with a thermocompression-bonding tool, and using a resin film having a higher tensile strength than PTFE as the resin film.

PTFE is used for the release film when thermocompression bonding is performed. (1) Prevention of ACF adhesion to thermocompression bonding tools, (2) Thickness variation in the object to be bonded (conductor / ACF / flying lead), set in the device This is to absorb the displacement and pressurize appropriately so as not to enlarge these deviations. However, since the degree of softening is large due to temperature rise during thermocompression bonding, the ACF in the molten or semi-molten state is pressed against the ACF from between the flying leads by pressing of the thermocompression bonding tool, and the conductor of the first printed wiring board It often flows out from the outside. In order to increase the connection strength of (conductor / flying lead), ACF does not flow out to the outside, but accumulates in a large amount in the space between (conductor / flying lead), and the (conductor / flying lead) on both sides of the space It is necessary to reach the upper part of the side surface and coat the side surface thickly. When PTFE is used for the release film, a large amount of ACF often flows out from between the conductors to the outside, and high adhesive strength cannot be obtained stably.
By using a resin film with a higher tensile strength than PTFE as the release film, it maintains a strength of a predetermined level or higher even when softened at high temperatures. , Not pushed at all. As a result, the ACF reaches the upper part of the side surface of the (conductor / flying lead) through the thermocompression bonding process, and can cover the side surface with a large thickness. As a result, the connection strength can be improved.

  The resin film can be adhered to the ACF and left on the second printed wiring board as a protective film. ACF can be adhered to the resin film between the flying leads. Thereby, the man-hour which arrange | positions a protective film later can be saved, ensuring high connection intensity | strength. In addition, after a predetermined number of uses, the release film itself to be discarded and the number of man-hours for disposal can be reduced.

  An adhesive layer is interposed between the second printed wiring board and the resin film, and the resin film can be left as a protective film on the second printed wiring board. Thereby, a protective film can be reliably provided in the outermost layer. And the man-hour which arrange | positions a protective film later can be saved, ensuring high connection intensity | strength. In addition, although the arrangement of the adhesive layer is expensive, it is possible to reduce the release film itself to be discarded and its disposal man-hour after a predetermined number of uses.

  After the thermal bonding process, it is possible to leave no resin film. Thereby, high connection strength can be ensured without providing a protective film.

  A super engineering plastic (SEP) film can be used as the resin film. As SEP, polyimide (PI), polyamideimide (PAI), polyetherimide (PEI), polyetheretherketone (PEEK), polyphenylene sulfide (PPS), with the condition that its tensile strength exceeds that of PTFE ), Polyarylate (PAR), liquid crystal polymer (LCP), polysulfone (PSU), polyethersulfone (PES), and fluororesin other than PTFE. Accordingly, it is possible to obtain the possibility of providing the protective film while securing the connection strength using the SEP that is relatively easy to purchase.

  The printed wiring board connection structure of the present invention includes a first printed wiring board having a plurality of conductors positioned on a substrate, a second printed wiring board having a plurality of flying leads, and a first printed wiring board. And an anisotropic conductive adhesive for connecting the second printed wiring board and the flying lead of the second printed wiring board, and a protective film positioned on the second printed wiring board. The tensile strength of the protective film is PTFE. It is characterized by being larger than the tensile strength. Thereby, as above-mentioned, high connection intensity | strength and a protective film can be obtained, saving a process.

  The protective film may be bonded to the ACF, or may have a structure in which an adhesive layer is provided between the protective film and the second printed wiring board and is bonded to the adhesive layer. As a result, depending on the structure of the flying lead and the like, it is possible to obtain a more appropriate structure by selection in consideration of economy.

  A super engineering plastic film can be used as the protective film.

  According to the printed wiring board and the wiring board connection structure of the present invention, the flying lead of one printed wiring board and the conductor wiring (board pad) of the other printed wiring board are sufficiently high while being electrically connected. Connection strength can be easily obtained.

The connection structure of the printed wiring board in Embodiment 1 of this invention is shown, (a) is a top view, (b) is sectional drawing which follows the IB-IB line. FIG. 3 is a diagram illustrating a state in which the flying lead of the second printed wiring board is aligned with the conductor of the first printed wiring board in the manufacture of the connection structure of the printed wiring board of FIG. 1. It is a figure which shows the process of thermocompression bonding in manufacture of the connection structure of the printed wiring board of FIG. The connection structure of the printed wiring board in the modification of Embodiment 1 of this invention is shown, (a) is a top view, (b) is sectional drawing which follows the IV-IV line. The connection structure of the printed wiring board in Embodiment 2 of this invention is shown, (a) is a top view, (b) is sectional drawing which follows the VB-VB line | wire. It is a figure which shows the process of thermocompression bonding in manufacture of the connection structure of the printed wiring board of FIG. It is sectional drawing which shows the form of ACF of invention example A1 in the Example of this invention. It is sectional drawing which shows the form of ACF of comparative example B1 in the Example of this invention.

(Embodiment 1)
1A and 1B show an example of a printed wiring board connection structure 50 according to Embodiment 1 of the present invention, in which FIG. 1A is a plan view and FIG. 1B is a cross-sectional view taken along line IB-IV. This printed wiring board connection structure 50 is roughly composed of (first printed wiring board 10 having conductor wiring 15 on substrate 11 / anisotropic conductive adhesive (ACF) 33 / seconding lead 25 having flying leads 25). It is a laminate of printed wiring board 20 / protective film 31).
In the first printed wiring board 10, for example, a conductor wiring (hereinafter referred to as a conductor) 15, which is patterned by etching with a copper foil attached to an insulating base material 11, is arranged in parallel at a predetermined interval. is doing. The exposed conductor 15 arranged on the insulating base material 11 in the printed wiring board 10 is a part for connection and may be called a board pad.
The ACF 33 is a thermosetting resin adhesive containing the conductive particles 33p, and the conductor 15 and the flying lead 25 are conductively connected by the ACF 33, and conductivity is not expressed in other portions. The conductive connection between the conductor 15 and the flying lead 25 is manifested by shortening the distance between the conductor 15 and the flying lead 25 so as to be approximately equal to the size of the conductive particles in the thermosetting or thermoplastic adhesive resin. The distance between the conductor 15 expressing the conductive connection and the flying lead 25 is, for example, 1 μm, and may be larger or smaller than this, and may be in the range of 0.1 μm to 5 μm. In FIG. 1B, the conductor 15 and the flying lead 25 are shown to be in direct contact with each other, but the ACF 33 is interposed therebetween, and in particular, the conductive particles 33p are conductively connected. . The conductive particles 33p may be any metal such as nickel or silver, or may be a resin particle obtained by gold plating, silver plating, or nickel plating. The shape may be any shape such as a spherical shape, a granular shape, or a needle shape.
A protective film 31 is disposed on the flying lead 25 or the second printed wiring board 20. The present embodiment is characterized in that a super engineering plastic (SEP) having a higher tensile strength than PTFE is used for the protective film 31. The advantage of using SEP will be described after the description of the method for manufacturing the printed wiring board connection structure 50 or the method for manufacturing the printed wiring board connection structure in the present embodiment.

2 and 3 are diagrams for explaining a method of manufacturing a connection structure that connects the conductor 15 of the first printed wiring board 10 and the flying lead 25 of the second printed wiring board 20. As shown in FIG. 2, the flying lead 25 is disposed so as to match the conductor 15 of the first printed wiring board 10 in plan view. Flying leads 25 between the space D ₂ of the width, i.e. the distance between the flying leads, the width of the space D ₁ of the between the conductors 15, i.e. are aligned to the spacing of the conductor 15. Space D ₁ of the between the conductors 15 of the first printed wiring board 10 is open to the side as well as above.
In the second printed wiring board 20, the flying lead 25, which is a conductor wiring, has one end extending from the insulating base material 21 and the other end entering the insulating base material 21. Between one end and the other end is bare. As shown in FIG. 2, the flying lead 25 may have a configuration in which the other end side is terminated in a bare state even when the wiring is formed by entering the insulating base 21 on both ends. The flying lead regions may be divided into a plurality of locations, and the regions may be arranged side by side or arranged in a staggered manner (in the case of three or more regions).

As shown in FIG. 3, the ACF 33 is arranged between the conductor 15 and the flying lead 25 so as to cross over all the parallel conductors 15. Therefore, the ACF 33 exhibits conductivity only between the flying lead 25 and the conductor 15 to which pressure is applied, and does not develop conductivity in the ACF located between (conductor 15 / flying lead 25). . The thermocompression bonding conditions are preferably a temperature of 100 ° C. to 300 ° C., a holding time of 5 seconds to 45 seconds, a pressure of 1 MPa to 9 MPa, for example, a temperature of 200 ° C., a holding time of 15 seconds, and a pressure of 3 MPa. This temperature is the temperature of ACF33. For this reason, the temperature of 200 ° C. under the above-mentioned thermocompression bonding conditions sets the temperature of the thermocompression bonding tool 41 incorporating the heater to a higher temperature so that the temperature of the ACF 33 becomes 200 ° C. The holding time is a time for pressing with the pressure by the pressing tool 41.
As described above, the ACF 33 contains a thermosetting resin or a thermoplastic resin as a main component. In the case of a thermosetting resin, a molten or semi-molten state passes in a transient temperature range up to the curing temperature. In the case of a thermoplastic resin, it is melted or semi-molten at a high temperature. Pressure is applied to the molten or semi-molten state to thin the conductor 15 / flying lead 25 portion so that the conductive particles are conducted inside the ACF 33. Further, the conductivity is prevented from appearing in other portions where pressure cannot be applied.
For the pressure load, it is preferable to use a pressing tool (thermocompression bonding tool) 41 having a width dimension that fits in the length range in which the flying lead 25 is exposed. Between the pressing tool 41 and the flying tool 25, A protective film 31 also serving as a release film is interposed. The release film or protective film 31 is disposed in order to prevent the ACF from sticking to the pressing tool 41. In this embodiment, the protective film 31 itself may adhere to the ACF 33, and the connection structure in FIG.

Conventionally, a PTFE (Polytetrafluoroethylene) film or a silicon rubber sheet has been used as a release film because it is a resin film that is difficult to adhere. At the time of thermocompression bonding, the pressing tool 41, the first and second printed wiring boards 10, 20 and the like of the thermocompression bonding apparatus shown in FIG. 3 are arranged in the air atmosphere. The ACF 33 was softened by heat conduction from the pusher 41 and was lost by flowing due to the pressure caused by the pressing of the PTFE film made into a release film.
The problem here is that the PTFE of the release film is softened due to the temperature rise, so that it is pushed by the pusher 41 to the space D ₂ between the flying leads 25 and further the space D ₁ between the conductors 15. In many cases, it goes into the area. In FIG. 3, the dotted line indicates the position of pressure application for the thermocompression bonding of the pusher 41. The PTFE film pushed between the flying leads 25 applies pressure to the ACF 33 located immediately below. As a result, when the PTFE film is used as a release film, the ACF 33 flows under pressure and flows out from the side openings between the conductors 15. However, in the embodiment of the present invention, an SEP film having a strength higher than that of PTFE is used for the release film. Softening Therefore release film is suppressed, from being pushed into the space D ₂ between the flying lead 25 is suppressed or prevented. As a result, ACF accumulates in the space between (conductor 15 / flying lead 25) and fills up to the upper part of the side surface of conductor 15 / flying lead 25, thereby contributing to improved connection strength. Since the ACF 33 adheres to the side surface of the (conductor 15 / flying lead 25) in a molten or semi-molten state, the ACF 33 is flat in the space D between the (conductor 15 / flying lead 25) as shown in FIG. It exhibits a surface shape peculiar to viscous fluids that does not exhibit a surface and hangs down from the side surface to the middle part. If the amount of accumulation of ACF 33 is large, this sag is not steep. If the drooping is steep, the coating thickness on the side surface of (conductor 15 / flying lead 25) becomes thin, and the connection strength becomes low.
The film used for the release film for thermocompression bonding is not required to have the property of being difficult to stick to the adhesive resin, has high tensile strength, and is required to be difficult to soften during thermocompression bonding. For this reason, an SEP film is used. For this SEP film, polyimide (PI), polyamideimide (PAI), polyetherimide (PEI), polyetheretherketone (PEEK), polyphenylene sulfide (PPS), polyarylate (PAR) ), Liquid crystal polymer (LCP), polysulfone (PSU), polyethersulfone (PES), and fluororesin other than PTFE. In order to transmit the pressure of the pusher 41 downward, the thickness is preferably 10 μm to 300 μm, for example, 50 μm.

Returning to FIG. 1, the protective film 31 is left as a protective film by being adhered to the ACF 33 in the space D ₂ between the flying leads 25 while being used as a release film. Since the release film uses SEP having a higher tensile strength than PTFE, it is softened during thermocompression bonding and is not pushed between the flying leads 25. For this reason, the ACF 33 can be filled to a predetermined level in the space D (= D ₁ + D ₂ ) between (conductor 15 / flying lead 25). That is, the sagging does not become steep, and the thickness of the coating on the side surface can be increased. As a result, the ACF 33 is located between the first printed wiring board 10 and the second printed wiring board 20, and conductively connects the conductor 15 and the flying lead 25, and the first printed wiring board. The connection strength between 10 and the second printed wiring board 20 is made sufficiently high.
The ACF 33 reaches the upper part of the side surface of the conductive connection (conductor 15 / flying lead 25), and exhibits a surface shape that accumulates along the side surface (hangs down) between the side surfaces (space D). The more ACFs that partially occupy between the side surfaces, the stronger the connection between the conductor 15 and the flying lead 25.

When the ACF 33 reaches the upper part of the side surface of the (conductor 15 / flying lead 25) and overflows, the protective film 31 that also serves as a release film is bonded between the flying leads 25, and the protective film 31 is the second film. It is fixed on the printed wiring board 20. In the connection region between the flying lead 25 and the conductor 15, the thickness of the conductor 15, the thickness of the flying lead 25, the space D (= D ₁ + D ₂ ), the thickness of the ACF 33 before thermocompression bonding, etc. Otherwise, the ACF 33 is usually designed to fill the space D without a gap. For this reason, by using SEP with high tensile strength for the release film, it is difficult to be pushed between the flying leads at the time of thermocompression bonding, so the outflow of ACF33 is suppressed and the space D is filled as described above or completely Even if it is not filled with (conductor 15 / flying lead 25), it can protrude from the upper part of the side surface and can be bonded to the SEP film 31 which also serves as a release film.
On the other hand, even when the SEP film 31 is slightly pushed between the flying leads 25, the degree of the pushing is smaller than that of PTFE, so that the ACF 33 does not flow out in a large amount. Then, the slightly pushed SEP film 31 and ACF 33 come into contact with each other, and the SEP film 31 is bonded to the ACF 33 and fixed on the second printed wiring board 20.
In summary, in any of the above cases, the SEP film 31 is bonded to the ACF 33 and fixed on the second printed wiring board 20. Such an SEP film 31 includes a conductor 15 → thin ACF containing conductive particles 33p → conductive connection locations of the flying leads 25, a stress transmission path of the first printed wiring board 10 → ACF 33 → SEP film 31, ACF 33 Since the stress transmission path such as the second printed wiring board 20 → the SEP film 31 is formed, the connection strength between the first printed wiring board 10 (conductor 15) and the second printed wiring board 20 (flying lead 25). To improve.
In this type of printed wiring board connection structure, it is rare that the flying leads 25 are left exposed, and in general, a protective film is usually provided in a later step. According to the present embodiment, the protective film 31 can be provided during thermocompression bonding without providing the protective film 31 in a subsequent process.
The first printed wiring board 10 does not have to be reinforced, but when reinforced, it is preferable to reinforce from the back surface. When reinforcing from the back side, a glass epoxy plate, a polyimide plate, a polyethylene terephthalate (PET) plate, a stainless plate, or the like having an appropriate thickness is preferably bonded.

  The first and second printed wiring boards 10 and 20 are preferably flexible printed wiring boards (FPC), but may be other types of printed wiring boards. In the case of a flexible printed wiring board, the insulating base materials 11 and 21 can use, for example, a resin having versatility for a printed wiring board, such as polyimide and polyester. In addition, it is particularly preferable to have high heat resistance in addition to flexibility, and as such a resin, for example, a polyamide-based resin or a polyimide-based resin such as polyimide or polyamideimide is preferable. used.

  The conductor 15 or the flying lead 25 can be formed by etching and processing a metal foil such as a copper foil by a conventional method. The conductor 15 can also be formed by plating by a semi-additive method. The thickness of the conductor 15 is preferably in the range of 10 μm to 30 μm, for example, 18 μm. The thickness of the flying lead 25 is preferably in the range of 10 μm to 25 μm, for example 20 μm.

  The ACF 33 is an anisotropic conductive adhesive having anisotropic conductivity containing the conductive particles 33p. When a thermosetting adhesive resin is used, an epoxy resin, a high molecular weight epoxy resin, a phenoxy resin, a curing agent And a thermosetting adhesive containing conductive particles as an essential component. As the ACF 33, for example, an epoxy resin and a phenoxy resin that are insulating thermosetting resins as main components and conductive particles such as nickel, copper, silver, and gold dispersed therein can be used. By using an epoxy resin, it becomes possible to improve the film formability, heat resistance, and adhesive strength of ACF33. The thickness of the ACF 33 is preferably in the range of 30 μm to 45 μm, for example 35 μm.

  Examples of the epoxy resin contained in the ACF 33 include bisphenol A type, F type, S type, AD type, or a copolymer type epoxy resin of bisphenol A type and bisphenol F type, naphthalene type epoxy resin, and novolak type. An epoxy resin, a biphenyl type epoxy resin, a dicyclopentadiene type epoxy resin, or the like can be used. Moreover, ACF33 should just contain at least 1 sort (s) among the above-mentioned epoxy resins.

  The molecular weight of the epoxy resin and the phenoxy resin can be appropriately selected in consideration of the performance required for the ACF 33. For example, when a high molecular weight epoxy resin is used, the film forming property is high, the melt viscosity of the resin at the connection temperature can be increased, and there is an effect that the connection can be made without disturbing the orientation of the conductive particles described later. On the other hand, when a low molecular weight epoxy resin is used, the effect of increasing the crosslink density and improving the heat resistance is obtained. Moreover, the effect of reacting with the above-mentioned hardening | curing agent rapidly at the time of a heating, and improving adhesive performance is acquired. Therefore, it is preferable to use a combination of a high molecular weight epoxy resin having a molecular weight of 15000 or more and a low molecular weight epoxy resin having a molecular weight of 2000 or less because the balance of performance can be achieved. In addition, the compounding quantity of a high molecular weight epoxy resin and a low molecular weight epoxy resin can be selected suitably. In addition, the “average molecular weight” herein means a weight molecular weight in terms of polystyrene determined by gel permeation chromatography (GPC) developed with THF.

  Moreover, ACF33 contains a latent curing agent as a curing agent, and a high adhesive force can be obtained by containing a curing agent for promoting the curing of the epoxy resin. A latent curing agent is a curing agent that is excellent in storage stability at low temperatures and hardly undergoes a curing reaction at room temperature, but rapidly undergoes a curing reaction by heat, light, or the like. Examples of such latent curing agents include imidazole, hydrazide, boron trifluoride-amine complexes, amine imides, polyamines, tertiary amines, alkyl ureas and other amines, dicyandiamides, acid anhydrides, Phenol-based compounds and modified products thereof are exemplified, and these can be used alone or as a mixture of two or more.

  Among these latent curing agents, an imidazole-based latent curing agent is preferably used from the viewpoint of excellent storage stability at a low temperature and rapid effect. As the imidazole-based latent curing agent, a known imidazole-based latent curing agent can be used. More specifically, an adduct of an imidazole compound with an epoxy resin is exemplified. Examples of the imidazole compound include imidazole, 2-methylimidazole, 2-ethylimidazole, 2-propylimidazole, 2-dodecylimidazole, 2-finylimidazole, 2-finyl-4-methylimidazole, and 4-methylimidazole.

  In particular, these latent curing agents coated with a polymer material such as polyurethane and polyester, a metal thin film such as nickel and copper, and an inorganic material such as calcium silicate, This is preferable because it is possible to achieve both contradictory properties of storage stability and fast curability. Therefore, a microcapsule type imidazole-based latent curing agent is particularly preferable.

Conductive particles are dispersed in the ACF 33, and the conductive particles include a large number of fine metal particles (for example, metal particles made of spherical metal particles or spherical resin particles plated with metal) in a linear form. It is formed of a metal powder having a connected shape or a needle shape, a shape having a large so-called aspect ratio. In the present embodiment, the proportion of conductive particles in ACF 33 is preferably 0.0001% by volume or more and 0.2% by volume or less.
Although the above explained in detail about the case where a thermosetting adhesive was used for ACF33, it is as above-mentioned that a thermoplastic resin may be used.

(Modification of Embodiment 1)
FIG. 4 is a modification of the first embodiment of the present invention, and shows a printed wiring board connection structure 50 according to one embodiment of the present invention, where (a) is a plan view and (b) is IVB. It is sectional drawing which follows the -IVB line. In this embodiment, the printed wiring board connection structure is formed by the method shown in FIGS. 2 and 3, but unlike the printed wiring board connection structure of FIG. 1, a resin film having a higher tensile strength than the PTFE film. The feature is that 31 is not left in the connection structure 50. The embodiment described later also corresponds to the printed wiring board connection structure 50 of this modification.
In order not to leave the resin film 31 in the printed wiring board connection structure 50, the resin film 31 is prevented from adhering to the ACF 33. To that end, (a1) the resin film 31 itself has releasability, or (a2) whether the operating conditions at the time of thermocompression bonding correspond to this modification.

(A1) As the resin film 31, for example, a fluororesin film having a higher tensile strength than PTFE can be used. Such high strength of the _{fluororesin, - (CF 2 -CF 2)} m - (CH 2 -CH 2) n - by the notation, ethylene - tetrafluoroethylene copolymer (ETFE: Ethylenetetrafluoroethylene-copolymer) be mentioned Can do. This fluororesin is excellent in releasability and high tensile strength. Moreover, it is not limited to a fluororesin, You may use such resin, if it is excellent in mold release property and tensile strength is higher than PTFE. The above ETFE can be used multiple times as a release film.

  Further, even if the releasability is not excellent, a resin film having a tensile strength higher than that of PTFE, for example, a general SEP film, has a releasability at a release treatment, for example, a thermocompression bonding temperature, before thermocompression bonding. What is necessary is just to apply the coating liquid with a high characteristic. As a result, during thermocompression bonding, the ACF 33 can be filled into the space D because it is softened and is not easily pushed between the flying leads 25. Moreover, since this resin film also has releasability by the above-mentioned coating treatment, it is not adhered to the ACF 33, and a structure without a protective film can be obtained as shown in FIG.

(A2) At the time of thermocompression bonding, by applying a thermal pattern such that the temperature range in which the fluidity of the ACF becomes high is applied for a long time, the ACF 33 is caused to flow out without being filled so as to exceed the space between the flying leads 25. To do. As a result, the resin film 31 becomes difficult to adhere to the ACF 33 between the flying leads 25, and the resin film 31 does not remain in the connection structure 50 after the thermocompression bonding process. It can be used repeatedly in the subsequent thermocompression bonding step.
A thermal pattern in which the temperature range in which the fluidity of the ACF 33 is increased for a long time is easier to configure with a thermoplastic resin than to use a thermosetting resin for the ACF 33. An appropriate resin is preferably selected for the ACF 33 depending on the connection structure.

  According to the present embodiment, the conductive strength of the first printed wiring board 10 and the flying lead 25 of the second printed wiring board 20 are conductively connected, and the connection strength between the printed wiring boards 10 and 20 is increased. can do. And the connection structure of this printed wiring board can be obtained without a protective film.

(Embodiment 2)
5A and 5B show a printed wiring board connection structure 50 according to Embodiment 2 of the present invention, in which FIG. 5A is a plan view and FIG. 5B is a cross-sectional view taken along line VB-VB. In the present embodiment, an SEP film having a high tensile strength is used as the protective film 31, and an adhesive 37 is disposed between the protective film 31 and the second printed wiring board 20 or the flying lead 25. Has characteristics. As a result, the SEP film 31 is firmly bonded to the second printed wiring board 20 or the flying lead 25.

  FIG. 6 is a diagram for explaining a method of manufacturing the printed wiring board connection structure 50 shown in FIG. A SEP film 31 for preventing adhesion between the pressing tool 41 and ACF or the like is disposed on the layer that hits the pressing tool 41, and an adhesive 37 is disposed under the SEP film 31. The adhesive 37 is preferably a film because it is easy to handle. For the adhesive 37, other compositions of ACF excluding conductive particles can be used. The thickness is preferably in the range of 3 μm to 25 μm, for example, about 9 μm. The laminated structure of the second printed wiring board 20 having the flying leads 25 / the ACF 33 / the first printed wiring board 10 having the conductor 15 is the same as that shown in FIG. The conditions at the time of thermocompression bonding are the same as the conditions in the first embodiment.

In this embodiment, since SEP film 31 will not be pushed into the space D ₂ between the flying lead 25, ACF33 is to fill the space D, it is possible to improve the connection strength.
Furthermore, the following advantages can be obtained by bonding the SEP film 31 with the adhesive 37. The SEP film 31 includes a conductor 15 → thin ACF including the conductive particles 33p → the conductive connection location of the flying lead 25, the first printed wiring board 10 → the ACF 33 → the adhesive 37 → the stress transmission path of the SEP film 31, and the ACF 33 A stress transmission path such as the second printed wiring board 20, the adhesive 37, and the SEP film 31 is formed. As a result, the SEP film 31 can contribute with higher contribution than the connection structure shown in FIG. 1 in the first embodiment to improve the connection strength between the printed wiring boards 10 and 20.

About the three test bodies of this invention example and two comparative examples, thermocompression bonding was performed and the form of a cross section, adhesion strength, etc. were measured. Manufacture of the test body was performed only by changing the resin type of the resin film 31 to be brought into contact with the thermocompression pressing tool, and other conditions were common to the inventive examples A1 to A3 and the comparative examples B1 to B2.
A single-sided FPC was used for the first printed wiring board. The width of the conductor is 100 μm, the height is 18 μm, and the distance between the conductors is 100 μm. A single-sided FPC was used for the second printed wiring board. The thickness of the flying lead was 20 μm, the width was 100 μm, and the interval was 100 μm. ACF using linear Ni particles was used for ACF, and the film thickness before thermocompression bonding was set to 35 μm. The thermocompression bonding conditions were a temperature of 200 ° C., a holding time of 15 seconds, and a pressure of 3 MPa, but the resin film (common with a thickness of 50 μm) in contact with the pressing tool was changed according to the test body. This example is a connection structure corresponding to the modified example (see FIG. 4) of the first embodiment in which the resin film is not left as a protective film.
After the test specimen was manufactured, the cross-sectional shape and adhesion strength were measured. The cross-sectional form was based on an optical microscope. The adhesion strength was measured according to the conductor peeling strength (8.1.1) defined in JIS C5016.
Invention Example A1: Polyimide film: Tensile strength 350 MPa
Invention Example A2: Polyetheretherketone (PEEK): Tensile strength 147 MPa
Invention Example A3: Polyetherimide (PEI): Tensile strength 114 MPa
Comparative Example B1: Polytetrafluoroethylene (PTFE): Tensile strength 43.9 MPa
Comparative Example B2: Silicon rubber film: Tensile strength 3.9 MPa

The results are shown in Table 1. The reference for the bottom thickness and connection strength of ACF was Comparative Example B1 (PTFE on resin film).
As in the prior art, in the printed wiring board connection structure 150 using the PTFE film as the release film, as shown in FIG. 8, the conductive connection between the conductor 115 on the substrate 111 and the flying lead 125 is performed. ACF 133 is mostly washed away and does not remain between (conductor 115 / flying lead 125). For this reason, the ACF 133 hardly contributes to the improvement of the connection strength. In Comparative Example B2 using silicon rubber, the results were almost the same or inferior to Comparative Example B1. 8 and 7 show the ACF of (conductor / flying lead) in a cross section.
On the other hand, as shown in FIG. 7, the connection structure manufactured by using a PI film as the resin film for preventing the adhesion of the pusher as in Example A1 of the present invention has a sufficiently thick bottom portion as shown in FIG. 15 / The connection strength between the first printed wiring board 10 and the second printed wiring board 20 can be sufficiently increased while obtaining the conductive connection of the flying lead 25. Similar results were obtained for the other Invention Examples A2 and A3. Accordingly, it was confirmed that the connection strength can be improved by using a SEP film having a strength higher than that of PTFE as the resin film applied to the pressing tool during the thermocompression bonding.

  Although the embodiments of the present invention have been described above, the embodiments of the present invention disclosed above are merely examples, and the scope of the present invention is not limited to these embodiments. The scope of the present invention is indicated by the description of the scope of claims, and further includes meanings equivalent to the description of the scope of claims and all modifications within the scope.

  According to the printed wiring board connection structure and the like of the present invention, a sufficiently high connection strength is obtained while electrically connecting the flying lead of one printed wiring board and the conductor wiring (board pad) of the other printed wiring board. It can be obtained easily, and it can cope with higher density of the substrate pads.

10 (first) printed wiring board, 11 base material, 15 conductor (wiring), 20 (second) printed wiring board, 21 base material, 25 flying lead, 31 high strength resin film, 33 ACF, 33p conductive particle , 37 adhesive, 41 pusher 50 connected structure of the wiring board, D (conductor / flying leads) space between, the space between _{D 1} conductors, _{D 2} space between the flying leads, the width of _{P w} pusher.

Claims (8)

A step of preparing a first printed wiring board in which a plurality of conductors are positioned on a substrate;
Arranging an anisotropic conductive adhesive film on the first printed wiring board;
A step of arranging a second printed wiring board having flying leads on the anisotropic conductive adhesive film in accordance with the first printed wiring board;
From the top of the second printed wiring board, comprising a step of thermocompression applying pressure with a thermocompression bonding tool with a resin film interposed therebetween,
A method for manufacturing a printed wiring board connection structure, wherein a resin film having a tensile strength greater than that of PTFE (Polytetrafluoroethylene) is used as the resin film.   2. The printed wiring according to claim 1, wherein the resin film is adhered to the anisotropic conductive adhesive, and the resin film is left as a protective film on the second printed wiring board. Manufacturing method of board connection structure.   2. The adhesive film is interposed between the second printed wiring board and the resin film, and the resin film is left as a protective film on the second printed wiring board. The manufacturing method of the connection structure of the printed wiring board of description.   The method for manufacturing a printed wiring board connection structure according to claim 1, wherein the resin film is not left after the thermal bonding step.   The method for manufacturing a printed wiring board connection structure according to claim 1, wherein a super engineering plastic film is used as the resin film. A first printed wiring board having a plurality of conductors located on the substrate;
A second printed wiring board having a plurality of flying leads;
An anisotropic conductive adhesive for connecting the conductor of the first printed wiring board and the flying lead of the second printed wiring board;
A protective film positioned on the second printed wiring board;
A printed wiring board connection structure, wherein the tensile strength of the protective film is greater than that of PTFE (Polytetrafluoroethylene).   The protective film is adhered to the anisotropic conductive adhesive, or includes an adhesive layer between the second printed wiring board and adhered to the adhesive layer. The printed wiring board connection structure according to claim 6.   The printed wiring board connection structure according to claim 6, wherein the protective film is a super engineering plastic film.

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