JP2004200501A - Wiring board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wiring board that is superior in connection reliability, without discontinuity between a wiring conductor and a wiring conductor layer, even if long-term thermal history is repeatedly applied over a long time. <P>SOLUTION: The wiring board is formed, by stacking alternately an insulation layer 1 that a heat resistance fiber substrate is impregnated with a thermosetting resin and a wiring conductor 2 and further stacking alternately an insulating resin layer 6 and a wiring conductor layer 7 on a core substrate 5 that is formed by electrically connecting the wiring conductors 2 located vertically with the insulation layer in-between, through a through-conductor 4 with a through-hole 3 formed in the insulation layer 1 is filled with a conductor material. The through-hole 3 that is formed in the insulation layer 1 on the outermost side of the core substrate 5 is made smaller in diameter from its internal side toward its surface side. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a wiring board on which electronic components such as semiconductor elements are mounted, and more particularly to a wiring board capable of forming wiring conductors on a core substrate surface at high density.
[0002]
[Prior art]
In general, modern electronic devices are required to be small, thin, lightweight, high-performance, high-performance, high-quality, and high-reliable, as represented by mobile communication devices. Electronic devices to be used are also required to be smaller and higher in density. For this reason, there is a demand for smaller, thinner, and more terminals for the wiring boards that make up the electronic device, and in order to realize this, the width of the wiring conductors including the signal conductors and the like have been reduced and the intervals thereof have been reduced. Further, high-density wiring has been achieved by increasing the number of wiring conductors.
[0003]
As a wiring board capable of such high-density wiring, a wiring board manufactured by employing a build-up method is known. This build-up wiring board is manufactured, for example, by the method described below.
[0004]
First, a laser beam is applied to an insulating sheet in which a reinforcing material such as glass cloth or non-woven aramid is impregnated with a thermosetting resin represented by an allyl-modified polyphenylene ether resin having heat resistance and chemical resistance. A through hole having a diameter of 100 to 200 μm on the light incident side and a diameter of 50 to 150 μm on the emission side is formed, and the through hole is filled with a conductive material containing tin, for example, to form a through conductor. Next, a wiring conductor made of, for example, copper foil is embedded in the insulating sheet on which the through conductor is formed so as to cover the through conductor and that the surface of the wiring conductor is flush with the surface of the insulating sheet. This is heat-cured to obtain a core substrate in which the wiring conductor is electrically connected to the through conductor and the wiring conductor is embedded in the insulating substrate.
[0005]
The wiring conductor is embedded in the insulating substrate so as to cover the through conductor, as described later, when the core substrate surface is physically or chemically roughened, the through conductor is exposed on the core substrate surface. This is because the through conductor is also removed, and the connection reliability between the through conductor and the wiring conductor is reduced. For this reason, the width of the wiring conductor is designed to be larger than the diameter of the through hole.
[0006]
Next, the surface of the core substrate is physically or chemically roughened, and further, a resin film made of a thermosetting resin such as an epoxy resin is adhered to the core substrate and then heat-cured to have a thickness of 20 to 200 μm. An insulating resin layer is formed. Thereafter, a via hole having a diameter of 50 to 200 μm is formed in the insulating resin layer located above the wiring conductor by irradiating a laser beam, and the surface of the insulating resin layer and the inner surface of the via hole are further exposed to a potassium permanganate solution or the like. The surface of the insulating resin layer and the inner surface of the via hole are coated with a conductor film made of copper plating using a semi-additive method to form a wiring conductor layer and a via conductor. Then, the build-up wiring board is manufactured by repeating the formation of the insulating resin layer and the via conductor / wiring conductor layer a plurality of times thereon.
[0007]
Note that when a laser beam is applied to the insulating layer or the insulating resin layer to form a through hole or a via hole, the diameter of the through hole or the via hole is larger on the laser light incident side than on the laser light emitting side. That is, the cross section in the thickness direction of the insulating layer or the insulating resin layer in the through hole or the via hole has a trapezoidal shape in which the bottom side on the laser light incident side is longer than the bottom side on the emission side. In addition, the conductive material can be filled into the through holes of the insulating layer at a high density by using a screen printing method from the opening side having a large diameter, that is, from the opening on the laser light incident side. As a result, the conduction resistance of the through conductor can be reduced. Further, the insulating layer on which the through conductor is formed is usually laminated such that the surface on the incident side or the surface on the emission side of the laser beam faces in the same direction from a series of processing flows.
[0008]
Also, in the trend of miniaturization of electronic components in recent years, miniaturization of wiring conductors is required in order to increase the density of wiring boards. Since the wiring conductors for connection between the formed wiring conductor and the wiring conductor layer formed on the insulating layer laminated on the core substrate are densely formed, the wiring conductor is further miniaturized on the surface of the core substrate. Is required.
[0009]
[Patent Document 1]
JP 2002-141630 A
[Problems to be solved by the invention]
However, in the conventional wiring board, the through-hole formed in at least one of the insulating layers located on the outermost side of the core substrate is formed such that the opening having the larger diameter is exposed on the surface of the core substrate. Therefore, the width of the wiring conductor cannot be made smaller than the opening diameter of the larger diameter of the through-hole, and there is a problem that the miniaturization and the high density of the wiring conductor are limited. .
[0011]
The present invention has been completed in view of the problems of the related art, and an object of the present invention is to provide a wiring board capable of forming wiring conductors at a high density on the surface of a core substrate.
[0012]
[Means for Solving the Problems]
The wiring board according to the present invention is configured such that an insulating layer formed by impregnating a heat-resistant fiber base material with a thermosetting resin and a wiring conductor formed of a metal foil are alternately laminated in a plurality of layers, and positioned vertically above and below the insulating layer. An insulating resin layer and a wiring conductor layer are alternately formed on a core substrate formed by electrically connecting the wiring conductors to each other by a through conductor formed by filling a through hole formed in the insulating layer with a conductive material. In a wiring board formed by laminating a plurality of layers, the diameter of the through hole formed in the insulating layer located on the outermost side of the core substrate is reduced from the inner side to the front side of the core substrate. It is characterized by the following.
[0013]
According to the wiring board of the present invention, the diameter of the through-hole formed in the insulating layer located on the outermost side of the core substrate is reduced from the inside of the core substrate to the surface side. The width of the wiring conductor to be formed can be made finer, and a wiring board capable of high-density wiring can be obtained. Also, by filling the inside of the through hole with the conductive material from the opening having the larger diameter, the filling density of the through conductor can be increased, and as a result, the conduction resistance of the through conductor can be reduced.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, the wiring board of the present invention will be described in detail with reference to the accompanying drawings.
[0015]
FIG. 1 is a cross-sectional view showing an example of an embodiment of a wiring board of the present invention, and FIG. 2 is an enlarged cross-sectional view of a main part thereof. In these figures, 1 is an insulating layer, 2 is a wiring conductor, 3 is a through hole, 4 is a through conductor, 5 is a core substrate, 6 is an insulating resin layer, and 7 is a wiring conductor layer. Is configured. In this example, an example is shown in which a wiring board is manufactured by applying three insulating resin layers 6 above and below a core substrate 5 formed by laminating four insulating layers 1.
[0016]
The core substrate 5 is a substantially rectangular substrate having a thickness of 0.15 to 1.5 mm, and has a function as a support for the insulating resin layer 6 and the wiring conductor layer 7 and a function to impart strength to the wiring substrate. When the thickness of the core substrate 5 is less than 0.15 mm, the rigidity of the wiring substrate is reduced, and the warpage tends to occur. When the thickness exceeds 1.5 mm, the wiring substrate is unnecessarily thick and the wiring substrate is reduced in weight. Tends to be difficult. Therefore, the thickness of the core substrate 5 is preferably in the range of 0.15 to 1.5 mm.
[0017]
The insulating layer 1 constituting the core substrate 5 has a thickness of 50 to 150 μm and has a function of supporting the wiring conductors 2 and ensuring insulation between the wiring conductors 2 positioned above and below, and is made of glass cloth or aramid. A heat-resistant fiber base material such as fiber or wholly aromatic ester fiber is impregnated with a thermosetting resin such as epoxy resin, bismaleimide triazine resin, or allyl-modified polyphenylene ether resin. If the thickness of the insulating layer 1 is less than 50 μm, handling tends to be difficult, and if it exceeds 150 μm, the thickness of the insulating layer 1 becomes unnecessarily thick, and it becomes difficult to increase the density of the wiring conductor 2. There is. Therefore, the insulating layer 1 preferably has a thickness of 50 to 150 μm.
[0018]
Such an insulating layer 1 is formed by impregnating a thermosetting resin precursor such as an epoxy resin or an allyl-modified polyphenylene ether resin into a heat-resistant fiber base material such as a glass cloth or an aramid fiber and semi-curing the insulating sheet. It is formed by manufacturing and heat-curing it.
[0019]
Further, in each of the insulating layers 1, a plurality of through conductors 4 are provided from the upper surface to the lower surface. These through conductors 4 have a function of electrically connecting the wiring conductors 2 located above and below the insulating layer 1, and mainly include tin in the through holes 3 formed by irradiating the insulating layer 1 with laser light. It is formed by embedding and thermosetting a conductive material composed of a metal powder as a component and a thermosetting resin.
[0020]
The through-hole 3 is pierced by irradiating a laser beam, so that the opening diameter of the laser beam on the incident side is larger than the opening diameter on the emission side. This is because a part of the laser light is reflected by the heat-resistant fiber base material inside the insulating layer 1, and the reflected laser light causes the laser light incident side portion of the insulating layer 1 to be excessively perforated. Is consumed inside the insulating layer 1, and the energy on the emission side becomes smaller than the energy on the incident side.
[0021]
Further, as described above, the opening diameter of the through hole 3 on the laser light incident side is larger than the opening diameter of the emission side. Since the conductive material is filled into the through hole 3 from the opening having the larger diameter, that is, from the opening on the laser light incident side, by using a screen printing method, the through conductor 4 Can be increased, and as a result, the conduction resistance of the through conductor can be reduced.
[0022]
The diameter of the through-hole 3 on the laser light incident side is preferably 30 to 200 μm. If the diameter of the laser beam incident side of the through-hole 3 is less than 30 μm, it tends to be difficult to fill the through-hole 3 with a conductive material satisfactorily. is there. Therefore, it is preferable that the diameter of the through hole 3 on the laser hole incident side be 30 to 200 μm.
[0023]
Further, the diameter of the through hole 3 on the laser beam emission side is preferably 20 to 160 μm. If the diameter of the through hole 3 on the laser light emission side is less than 20 μm, it tends to be difficult to fill the through hole 3 with a conductive material, and if it exceeds 160 μm, it becomes difficult to miniaturize the wiring conductor 2. There is. Therefore, it is preferable that the diameter of the through hole 3 on the laser hole emission side be 30 to 200 μm.
[0024]
Although it is possible to drill a small through hole 3 in the core substrate 5 using a small diameter drill, when the fine through hole 3 is drilled using a drill, the diameter of the through hole 3 is reduced. It becomes the same from top to bottom, and it becomes difficult to fill the through hole 3 with the conductive material, and it tends to be difficult to increase the filling density of the through conductor 4.
[0025]
Further, the content of the metal powder of the conductive material is preferably 80 to 95% by mass. When the content of the metal powder is less than 80% by mass, the thermosetting resin tends to hinder the connection between the metal powders and increase the conduction resistance. When the content exceeds 95% by mass, the viscosity of the conductive material increases. Tend to be too good to be embedded. Therefore, the content of the metal powder of the conductive material is preferably 80 to 95% by mass.
[0026]
Such a metal powder is preferably made of an alloy of tin, silver, bismuth, and copper, and particularly preferably contains 30 to 80% by mass of tin when the wiring conductor 2 described later is made of copper foil. When the tin content is 30 to 80% by mass, a copper-tin alloy is favorably formed with the copper foil forming the wiring conductor 2, and the connection resistance between the through conductor 4 and the wiring conductor 2 is reduced. Can be.
[0027]
The average particle size of the metal powder is preferably 4 to 6 μm. If the average particle size is smaller than 4 μm, the viscosity of the conductive material tends to be too high to be satisfactorily embedded. Electric resistance tends to increase. Therefore, the average particle size of the metal powder is preferably 4 to 6 μm.
[0028]
The thermosetting resin is preferably a triazine-based thermosetting resin such as triallyl cyanurate or triallyl isocyanurate / tris epoxypropyl isocyanurate / tris (2-hydroxyethyl) isocyanurate.
[0029]
Such through holes 3 are formed at predetermined positions of the insulating sheet by employing a conventionally known method such as a carbon dioxide gas laser or a YAG laser. Then, a conductive material containing a metal powder containing tin as a main component and a thermosetting resin precursor such as a triazine-based resin is filled by a screen printing method (press-fitting) from an opening having a larger diameter of the through hole 3. Thereby, the through conductor 4 is formed.
[0030]
A wiring conductor 2 is embedded in the surface of each insulating layer 1. The wiring conductor 2 has a width of 20 to 200 μm and a thickness of 5 to 50 μm, and is made of metal foil such as copper, aluminum, nickel, silver, and gold, and may be made of copper foil from the viewpoint of workability and low cost. preferable. If the width of the wiring conductor 2 is less than 20 μm, deformation and disconnection of the wiring conductor 2 tend to occur easily, and if it exceeds 200 μm, high-density wiring tends not to be formed. Further, when the thickness of the wiring conductor 2 is less than 5 μm, the strength of the wiring conductor 2 tends to decrease and deformation or disconnection tends to occur, and when it exceeds 50 μm, it tends to be difficult to embed the insulating layer 1. . Therefore, the wiring conductor 2 preferably has a width of 20 to 200 μm and a thickness of 5 to 50 μm.
[0031]
Such a wiring conductor 2 is formed by etching a copper foil applied over the entire surface of a transfer sheet made of a heat-resistant resin such as polyethylene terephthalate (PET) resin via an adhesive into a predetermined pattern, and the transfer sheet is formed. Is placed on an uncured insulating sheet serving as the insulating layer 2 such that the predetermined through conductors 4 and the wiring conductors 2 are connected and the wiring conductors 2 cover the through conductors 4, and this is heated. The wiring conductor 2 is transferred and embedded in the insulating sheet by pressing for several minutes at a temperature of 100 to 150 ° C. using a press machine. Furthermore, the number of pressure of the transfer sheet was superimposed insulating sheet was peeled off the transfer sheet with peeling of an insulating sheet on a plurality vertically temperature of 150 to 240 ° C. using a hot press and 3 to 5 × 10 ⁶ Pa The core substrate 5 is manufactured by heating and pressing for a time.
[0032]
The reason why the wiring conductor 2 is embedded in the insulating layer 2 so as to cover the through conductor 4 is that when the surface of the core substrate 5 is physically or chemically roughened, the If exposed on the surface, the penetrating conductor 4 is also removed, and the connection reliability between the penetrating conductor 4 and the wiring conductor 2 is reduced. Therefore, it is important to make the width of the wiring conductor 2 larger than the diameter of the through conductor 4 and embed the wiring conductor 2 in the insulating layer 2 so as to cover the through conductor 4.
[0033]
In the wiring board of the present invention, the diameter of the through hole 3 formed in the insulating layer 1 located on the outermost side of the core substrate 5 decreases from the inner side to the front side of the core substrate 5. This is also important.
[0034]
According to the wiring board of the present invention, since the diameter of the through hole 3 formed in the insulating layer 1 located on the outermost side of the core substrate 5 decreases from the inner side to the front side of the core substrate 5, Since the opening diameter of the through hole 3 connected to the wiring conductor 2 can be reduced, the width of the wiring conductor 2 can be reduced, and as a result, the wiring conductor 2 can be miniaturized and a wiring board capable of high-density wiring can be obtained. be able to.
[0035]
Further, a plurality of insulating resin layers 6 and wiring conductor layers 7 are alternately laminated on the surface of the core substrate 5. The insulating resin layer 6 has a function as a support of the wiring conductor layer 7, has a thickness of 10 to 80 μm, and has an epoxy resin and silica having an average particle size of 0.01 to 2 μm and a content of 10 to 50 mass%. And inorganic insulating fillers such as alumina and aluminum nitride.
[0036]
The inorganic insulating filler adjusts the coefficient of thermal expansion of the insulating resin layer 6 so as to match the coefficient of thermal expansion of the wiring conductor layer 7, and forms moderate irregularities on the surface of the insulating resin layer 6, thereby forming the wiring conductor layer 7 and the insulating resin. It has a function of improving adhesion to the layer 6. If the average particle size of the inorganic insulating filler is less than 0.01 μm, it tends to be difficult to form the insulating resin layer 6 having a uniform thickness by agglomeration of the inorganic insulating fillers, and more than 2 μm. In addition, the irregularities on the surface of the insulating resin layer 6 become too large, so that fine wiring of the wiring conductor layer 7 cannot be formed, and high-density wiring tends to be difficult. Therefore, the average particle size of the inorganic insulating filler is preferably in the range of 0.01 to 2 μm.
[0037]
When the content of the inorganic insulating filler is less than 10% by mass, the effect of adjusting the thermal expansion coefficient of the insulating resin layer 6 is reduced, and the core substrate 5 and the insulating resin layer 6 tend to be easily separated. If the content exceeds 50% by mass, the amount of resin in the insulating resin layer 6 decreases, and water tends to stay between the inorganic insulating fillers, and the insulating property of the insulating resin layer 6 after absorbing moisture tends to decrease. Therefore, the content of the inorganic insulating filler is preferably in the range of 10 to 50% by mass.
[0038]
Via holes 8 are formed in the insulating resin layer 6 by laser processing. Via conductors 9 are formed by applying a part of a wiring conductor layer 7 made of copper plating to the inside of the via holes 8. In addition, the wiring conductors 2 and the wiring conductor layers 7 located above and below the insulating resin layer 6 are electrically connected to each other.
[0039]
The wiring conductor layer 7 has a width of 20 to 200 μm, a thickness of 1 to 2 μm, and an electroless copper plating layer of 10 to 30 μm in thickness, and is mounted on a wiring board. It has a function as a conductive path for electrically connecting each electrode of an electronic component (not shown) such as a semiconductor element to an external electric circuit board (not shown).
[0040]
When the width of the wiring conductor layer 7 is less than 20 μm, deformation and disconnection of the wiring conductor layer 7 tend to occur easily, and when it exceeds 200 μm, high-density wiring tends not to be formed. Further, if the thickness of the wiring conductor layer 7 is less than 11 μm, the strength of the wiring conductor layer 7 tends to decrease and deformation or disconnection tends to occur, and if it exceeds 32 μm, it takes a long time to form the wiring conductor layer 7. Tend to be. Therefore, it is preferable that the wiring conductor layer 7 has a width in the range of 20 to 200 μm and a thickness in the range of 11 to 32 μm.
[0041]
A part of the wiring conductor layer 7 formed on one outermost layer surface of the insulating resin layer 6 has a mounting electrode 10a for connecting an electronic component, which is joined to each electrode of the electronic component via a conductor bump 11a. A part of the wiring conductor layer 7 formed and formed on the other outermost layer surface of the insulating resin layer 6 is connected to each electrode of the external electric circuit board via the conductor bump 11b, and is used as an external connection mounting electrode. 10b.
[0042]
The surface of the mounting electrodes 10a and 10b is coated with nickel having good wettability with solder and excellent corrosion resistance in order to prevent the oxidative corrosion and to make the connection with the conductor bumps 11a and 11b good. A plating layer of gold or the like is applied;
[0043]
The outermost insulating layer 1 and the mounting electrodes 10a and 10b are coated with a solder-resistant resin layer 12 having an opening for exposing the central portion of the mounting electrodes 10a and 10b as necessary. The solder-resistant resin layer 12 has a thickness of 10 to 50 μm. For example, 30 to 70% by mass of an inorganic powder filler such as silica or talc is added to a mixture of a photosensitive resin such as an acrylic-modified epoxy resin and a photoinitiator. To prevent the adjacent mounting electrodes 10a and 10b from being electrically short-circuited by the conductive bumps 11a and 11b, and to join the mounting electrodes 10a and 10b to the insulating resin layer 6. Has the function of improving strength.
[0044]
Such a solder-resistant resin layer 12 is formed by applying an uncured resin film composed of a photosensitive resin, a photoinitiator, and an inorganic powder filler on the surface of the outermost insulating resin layer 6 or by forming a thermosetting resin and an inorganic resin. An uncured resin varnish comprising a powder filler is applied to the surface of the outermost insulating resin layer 6 and dried, and thereafter, an opening is formed by exposure and development, and this is formed by UV curing and heat curing. You.
[0045]
Thus, the wiring board of the present invention has an electronic device by mounting electronic components such as semiconductor elements on this surface and connecting each electrode to the mounting electrode 10a for connecting the electronic component via the conductive bump 11a. By connecting the mounting electrodes 10b to the external electric circuit board via the conductor bumps 11b, the mounted electronic components are electrically connected to the external electric circuit board.
[0046]
The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the present invention.
[0047]
【The invention's effect】
According to the wiring board of the present invention, the diameter of the through hole formed in the insulating layer located on the outermost side of the core substrate is reduced from the inside of the core substrate to the surface side. The width of the wiring conductor to be formed can be made finer, and a wiring substrate capable of high-density wiring can be obtained. Further, by filling the inside of the through hole with the conductive material from the opening having the larger diameter, the filling density of the through conductor can be increased, and as a result, the conduction resistance of the through conductor can be reduced.
[Brief description of the drawings]
FIG. 1 is a sectional view showing an example of an embodiment of a wiring board of the present invention.
FIG. 2 is an enlarged sectional view of a main part of FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Insulating layer 2 ... Wiring conductor 3 ... Through hole 4 ... Through conductor 5 ... Core substrate 6 ... ..Insulating resin layer 7 ... Wiring conductor layer

Claims (1)

While alternately laminating a plurality of wiring layers made of a metal foil and an insulating layer formed by impregnating a heat-resistant fiber base material with a thermosetting resin, the wiring conductors located vertically above and below the insulating layer, Wiring formed by alternately stacking a plurality of insulating resin layers and wiring conductor layers on a core substrate formed by electrically connecting through-holes formed in the insulating layer with a through-hole conductor filled with a conductive material. A wiring board, wherein the diameter of the through hole formed in the insulating layer located on the outermost side of the core board in the board decreases from the inside to the surface of the core board.

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