WO2013099204A1

WO2013099204A1 - Wiring board and manufacturing method therefor

Info

Publication number: WO2013099204A1
Application number: PCT/JP2012/008234
Authority: WO
Inventors: 亮人岩崎; 中村　禎志; 檜森　剛司; 本城　和彦
Original assignee: パナソニック株式会社
Priority date: 2011-12-26
Filing date: 2012-12-25
Publication date: 2013-07-04

Abstract

A wiring board comprises: an electrically insulated base material comprising a non-compressed member and a thermosetting member; a first wiring and a second wiring that are formed with the electrically insulated base material interposed therebetween; and via-hole conductors that penetrate the electrically insulated base material, and electrically connect the first wiring and the second wiring. The via-hole conductors comprise resin sections and metal sections. The metal sections comprise first metal sections the main ingredient of which is Cu, second metal sections the main ingredient of which is Sn-Cu alloy, and third metal sections the main ingredient of which is Bi. The second metal section is larger than the first metal section, and larger than the third metal section.

Description

Wiring board and manufacturing method thereof

The present invention relates to a wiring board for connecting wirings formed on both surfaces of an electrically insulating base material by via-hole conductors and a manufacturing method thereof.

There is known a wiring board for connecting wirings formed at both ends of an electrically insulating substrate by via-hole conductors in which holes formed in the electrically insulating substrate are filled with a conductive paste. Also, a via-hole conductor is known in which metal particles containing copper (Cu) are filled instead of the conductive paste and the metal particles are fixed with an intermetallic compound. Specifically, by heating a conductive paste containing tin (Sn) -bismuth (Bi) -based metal particles and copper particles at a predetermined temperature, tin (Sn) -copper (Cu) is formed around the copper particles. Via hole conductors in which alloys are formed are known.

FIG. 14 is a schematic cross-sectional view of a via-hole conductor of a conventional wiring board. 15A and 16A are views showing SEM photographs of a conventional via-hole conductor. FIG. 15B is a schematic diagram of FIG. 15A. FIG. 16B is a schematic diagram of FIG. 16A. The magnification of FIG. 15A is 3000 times, and the magnification of FIG. 16A is 6000 times.

The via-hole conductor 2 is in contact with the wiring 1 formed on the surface of the wiring board. The via-hole conductor 2 has a metal part 11 and a resin part 12. The metal portion 11 is mainly composed of a first metal region 8 having a plurality of copper (Cu) -containing particles 3, a second metal region 9 made of tin (Sn) -copper (Cu) alloy, and the like, and bismuth (Bi). And a third metal region 10. As a prior art document related to the present invention, for example, Patent Document 1 is known.

Japanese Patent No. 4713682

The wiring board of the present invention includes an electrically insulating base material having an incompressible member and a thermosetting member, a first wiring and a second wiring formed with the electrically insulating base material interposed therebetween, and electrical insulation. A via-hole conductor that penetrates the conductive substrate and electrically connects the first wiring and the second wiring. The via-hole conductor has a resin portion and a metal portion. The metal portion includes a first metal region mainly composed of copper (Cu), a second metal region mainly composed of tin (Sn) -copper (Cu) alloy, and a first metal region mainly composed of bismuth (Bi). 3 metal regions. The second metal region is larger than the first metal region and larger than the third metal region.

FIG. 1A is a schematic cross-sectional view of a wiring board according to an embodiment of the present invention. FIG. 1B is a schematic cross-sectional view of the vicinity of the via-hole conductor in the embodiment of the present invention. FIG. 2A is a cross-sectional view showing a method for manufacturing a wiring board in an embodiment of the present invention. FIG. 2B is a cross-sectional view showing the method for manufacturing the wiring board in the embodiment of the present invention. FIG. 2C is a cross-sectional view showing the method for manufacturing the wiring board in the embodiment of the present invention. FIG. 2D is a cross-sectional view showing the method for manufacturing the wiring board in the embodiment of the present invention. FIG. 3A is a cross-sectional view showing a method for manufacturing a wiring board in an embodiment of the present invention. FIG. 3B is a cross-sectional view showing the method for manufacturing the wiring board in the embodiment of the present invention. FIG. 3C is a cross-sectional view showing the method for manufacturing the wiring board in the embodiment of the present invention. FIG. 4A is a cross-sectional view showing a method for manufacturing a multilayer wiring board in accordance with the exemplary embodiment of the present invention. FIG. 4B is a cross-sectional view showing the method for manufacturing the multilayer wiring board in the embodiment of the present invention. FIG. 4C is a cross-sectional view showing the method for manufacturing the multilayer wiring board in the embodiment of the present invention. FIG. 5A is a schematic cross-sectional view of the vicinity of the via-hole conductor before the via paste is compressed. FIG. 5B is a schematic cross-sectional view of the vicinity of the via-hole conductor after the via paste is compressed. FIG. 6 is a schematic diagram showing the state of via paste when a member having compressibility is used. FIG. 7 is a schematic view showing a state of via paste when an incompressible member is used. FIG. 8 is a schematic diagram showing a state of via paste when an incompressible member is used. FIG. 9A is a schematic diagram showing the state of the via paste before the alloying reaction. FIG. 9B is a schematic diagram showing a state of the via-hole conductor after the alloying reaction. FIG. 10 is a triangular diagram showing a metal composition in the via paste in the embodiment of the present invention. FIG. 11A is a diagram showing an SEM photograph of the via-hole conductor in the embodiment of the present invention. FIG. 11B is a schematic diagram of FIG. 11A. FIG. 12A is a diagram showing an SEM photograph of the via-hole conductor in the embodiment of the present invention. FIG. 12B is a schematic diagram of FIG. 12A. FIG. 13 is a diagram showing an analysis result by X-ray diffraction of the via-hole conductor in the embodiment of the present invention. FIG. 14 is a schematic cross-sectional view of a via-hole conductor of a conventional wiring board. FIG. 15A is a view showing an SEM photograph of a conventional via-hole conductor. FIG. 15B is a schematic diagram of FIG. 15A. FIG. 16A is a view showing an SEM photograph of a conventional via-hole conductor. FIG. 16B is a schematic diagram of FIG. 16A.

When the conventional via-hole conductor 2 is subjected to thermal shock during reflow processing or the like, Cu diffuses into the Sn—Bi-based metal particles, and intermetallic compounds such as Cu ₃ Sn and Cu ₆ Sn ₅ are generated. At that time, as shown in FIG. 14, voids 5 a and cracks 5 b may be generated in the via-hole conductor 2. Further, when Cu ₆ Sn ₅ changes to Cu ₃ Sn, Kirkendyl voids or the like may occur. Furthermore, due to the presence of the void 5a, internal stress may be generated in the via-hole conductor 2 when Cu ₆ Sn ₅ formed at the interface between Cu and Sn changes to Cu ₃ Sn by heating.

Further, the conventional via hole conductor 2 has a large volume fraction of the resin portion 12 occupying the via hole conductor 2 and a small volume fraction of the metal portion 11. Therefore, the via resistance (the resistance value of the entire via hole conductor 2) may be high.

Hereinafter, the structure of the multilayer wiring board of the present embodiment will be described.

FIG. 1A is a schematic cross-sectional view of a multilayer wiring board according to an embodiment of the present invention. A plurality of wirings 120 formed inside the electrically insulating base material 130 are electrically connected via via-hole conductors 140 to constitute a multilayer wiring board 110.

FIG. 1B is a schematic cross-sectional view of the vicinity of the via-hole conductor 140 in the embodiment of the present invention. The multilayer wiring board 110 includes an electrically insulating base material 130 having an incompressible member 220 and a thermosetting adhesive layer (thermosetting member) 210, a first wiring 120a, a second wiring 120b, and a via-hole conductor. 140. The first wiring 120a and the second wiring 120b are formed with the electrically insulating base material 130 interposed therebetween. The via-hole conductor 140 penetrates the electrically insulating base material 130 and electrically connects the first wiring 120a and the second wiring 120b.

The electrically insulating substrate 130 has an incompressible member 220 such as a heat resistant film, and a thermosetting adhesive layer (thermosetting member) 210 formed on both surfaces of the incompressible member 220. A first wiring 120 a and a second wiring 120 b obtained by patterning a metal foil 150 such as a copper foil into a predetermined shape are bonded to the incompressible member 220 through a thermosetting adhesive layer 210. The thermosetting adhesive layer 210 may be formed only on one surface of the incompressible member 220.

The via-hole conductor 140 has a metal part 190 and a resin part 200. The metal portion 190 has a first metal region 160 mainly composed of copper, a second metal region 170 mainly composed of a tin-copper alloy, and a third metal region 180 mainly composed of bismuth. Second metal region 170 is larger than first metal region 160 and larger than third metal region 180.

Resin portion 200 is an epoxy resin or the like. Epoxy resins are excellent in reliability. The resin portion 200 is mainly a cured product of the resin added to the via paste, but a part of the thermosetting resin constituting the thermosetting adhesive layer 210 may be mixed therein.

The size (or volume fraction or weight fraction) of the second metal region 170 is larger than the size (or volume fraction or weight fraction) of the first metal region 160. Furthermore, the size (or volume fraction or weight fraction) of the second metal region 170 is larger than the size (or volume fraction or weight fraction) of the third metal region 180.

By making the size of the second metal region 170 larger than the size of the first metal region 160 and larger than the size of the third metal region 180, the plurality of wirings 120 are electrically connected with the second metal region 170 as a main component. it can. Furthermore, the first metal region 160 and the third metal region 180 can be scattered in the second metal region 170 without being in contact with each other (or scattered in a small islet state).

The second metal region 170 has an intermetallic compound Cu ₆ Sn ₅ and an intermetallic compound Cu ₃ Sn, and the ratio of Cu ₆ Sn ₅ / Cu ₃ Sn is 0.001 or more and 0.100 or less. By reducing the amount of _{_{_{Cu 6 Sn 5, Cu 6 Sn}}} 5 remaining in the multilayer wiring board 110, in the heat treatment step such as a solder reflow it can be prevented from being changed to _Cu 3 Sn. As a result, the generation of Kirkendall voids and the like is suppressed.

The ratio of Cu ₆ Sn ₅ / Cu ₃ Sn is preferably 0.100 or less. It is more desirable to set it to 0.001 or more and 0.100 or less. The reaction time is finite, and the reaction time is practically 10 hours or less at the longest. Therefore, in such a finite reaction time, the ratio of Cu ₆ Sn ₅ / Cu ₃ Sn is unlikely to be completely zero, and it is difficult to quantitatively analyze Cu ₆ Sn ₅ that will remain slightly. Become.

As described above, when a normal measuring device is used, Cu ₆ Sn ₅ may not be detected (for example, the detection amount becomes 0 due to the detection limit of the measuring device). Therefore, when a normal measuring device is used, the ratio of Cu ₆ Sn ₅ / Cu ₃ Sn is 0 or more and 0.100 or less (note that 0 is below the detection limit of the measuring device or could not be detected by the measuring device). Including cases). Note that when the measurement accuracy of the measurement device is sufficiently high, the ratio of Cu ₆ Sn ₅ / Cu ₃ Sn may be 0.001 or more and 0.100 or less.

The reason why the ratio of Cu ₆ Sn ₅ / Cu ₃ Sn is preferably 0.001 or more and 0.100 or less is the result of evaluation using an XRD (X-ray diffractometer). However, it is difficult to extract only a fine via portion (or via paste portion) constituting an actual wiring board and analyze it by using an XRD apparatus. Therefore, a general evaluation apparatus, for example, an elemental analysis apparatus (for example, XMA, EPMA, etc.) using fluorescent X-rays attached to an SEM apparatus may be used as the measurement apparatus. Even when such an elemental analyzer (for example, XMA, EPMA, etc.) is used, the ratio of Cu ₆ Sn ₅ / Cu ₃ Sn is preferably 0.001 or more and 0.100 or less. XRD is a kind of mass analysis and EPMA is a kind of cross-sectional analysis, but there is substantially no difference. From the above, when measuring the ratio of Cu ₆ Sn ₅ / Cu ₃ Sn in the fine via portion (or via paste portion), select one of XRD, XMA, EPMA, or a similar device for evaluation. That's fine.

The electrically insulating substrate 130 has an incompressible member 220 such as a heat resistant film and a thermosetting adhesive layer 210 formed on at least one surface thereof.

In this embodiment, it is practical to define the definition of compressibility and incompressibility depending on the configuration of the core material. That is, a member using a woven fabric or a nonwoven fabric in which a plurality of fibers are entangled with each other as a core material, whether glass fiber or resin fiber, has compressibility. This is because a through-hole is formed in a core material using a woven fabric or non-woven fabric, and when this through-hole is filled with a conductive paste and pressed, it is pressed against metal particles contained in the conductive paste. This is because the through hole is deformed or widened.

On the other hand, since a member using a film as a core material has no space inside, it has incompressibility. This is because a through-hole is formed in a core material using a film, and when the through-hole is filled with a conductive paste and pressed, the diameter of the through-hole does not substantially change.

In addition, when a woven fabric or nonwoven fabric using glass fiber is used as a core material, when a through hole is formed with a laser or the like, the tip of the woven fabric or nonwoven fabric made of glass fiber around the hole may melt and harden, Even in this case, the core material has compressibility. The reason for this is that the presence of glass fiber melted and integrated with a laser or the like is limited only to the periphery of the hole, and the glass fiber in the other part (that is, the part slightly away from the through hole formed by the laser) This is because they are only intertwined with each other. Moreover, it is because all the glass fibers exposed around the hole do not melt and become one.

In the case of a nonwoven fabric using glass fibers, the entangled portions of the fibers may be fixed. Even in this case, the member having the nonwoven fabric as the core material has compressibility.

The incompressible member 220 has excellent incompressibility because it does not have a bubble portion or the like for expressing compressibility inside.

By using an incompressible member, the via paste can be compressed at a high pressure. As a result, a via-hole conductor 140 having a metal part 190 of 74.0 vol% or more and 99.5 vol% or less and a resin part 200 of 0.5 vol% or more and 26.0 vol% or less can be produced.

By reducing the volume fraction (vol%) of the resin portion 200 that is an insulating component in the via-hole conductor 140, the volume fraction (vol%) of the metal portion 190 increases and the via resistance decreases. Here, the via resistance means a resistance value of the entire via-hole conductor 140. In order to increase the mechanical strength of the via portion, it is preferable to increase the volume fraction of the metal portion 190 in the via-hole conductor 140.

Furthermore, the connection resistance between the wiring 120 and the via-hole conductor 140 is reduced by increasing the contact area between the wiring 120 and the via-hole conductor 140. Therefore, it is preferable to reduce the volume fraction of the resin part 200 at the interface part between the wiring 120 and the via-hole conductor 140.

With the configuration of this embodiment, the specific resistance of the via-hole conductor 140 can be set to 1.00 × 10 ⁻⁷ Ω · m or more and 5.00 × 10 ⁻⁷ Ω · m or less, so that the via resistance is stable. Turn into.

Furthermore, in this embodiment, the alloying reaction between copper and tin is almost completely completed.

In addition, the resin part 200 which comprises the via-hole conductor 140 consists of hardened | cured material of curable resin. Although the curable resin is not particularly limited, specifically, for example, it is preferable to use a cured product of an epoxy resin that is excellent in heat resistance and has a low linear expansion coefficient.

An example of a method for manufacturing the wiring board 600 and the multilayer wiring board 111 will be described below. 2A to 2D and FIGS. 3A to 3C are cross-sectional views showing a method for manufacturing the wiring substrate 600. FIG. 4A to 4C are cross-sectional views showing a method for manufacturing the multilayer wiring board 111. FIG.

The uncured base material 230 (base material) has an incompressible member 220 having a thickness of 55 μm or less, and an uncured thermosetting adhesive layer 210 formed on both surfaces of the incompressible member 220.

First, as shown in FIG. 2A, protective films 240 are bonded to both surfaces of the uncured base material 230. The incompressible member 220 can obtain sufficient insulation even when the thickness is 50 μm or less, 30 μm or less, 15 μm or less, and even 6 μm or less.

As the incompressible member 220, for example, a polyimide film, a liquid crystal polymer film, a polyether ether ketone film, or the like is used. Among these, a polyimide film is particularly preferable, but is not particularly limited as long as it is a resin sheet that can withstand the soldering temperature.

As the thermosetting adhesive layer 210, an uncured adhesive layer made of an epoxy resin or the like is used. In order to reduce the thickness of the multilayer wiring board, the thickness of one side of the thermosetting adhesive layer is preferably 1 μm or more and 30 μm or less, more preferably 5 μm or more and 10 μm or less.

As the protective film, for example, a resin film such as PET (polyethylene terephthalate) or PEN (polyethylene naphthalate) is used. The thickness of the resin film is preferably 0.5 μm or more and 50 μm or less, and more preferably 1 μm or more and 30 μm or less. By setting it as such thickness, the protrusion part which consists of via paste of sufficient height can be exposed by peeling of a protective film so that it may mention later.

As a method of bonding the protective film 240 to the uncured substrate 230, for example, the surface tackiness (or adhesive force) of the uncured substrate 230 or the thermosetting adhesive layer 210 on the surface of the uncured substrate 230 is used. A method of directly bonding is used.

Next, as shown in FIG. 2B, a through-hole 250 is formed by perforating the uncured base material 230 on which the protective film 240 is disposed from the outside of the protective film 240. For the drilling, various methods such as drilling using a drill as well as non-contact processing methods such as a carbon dioxide laser and a YAG laser are used. The diameter of the through hole is 10 μm or more and 500 μm or less, and further 50 μm or more, 300 μm or less, 80 μm or more, 120 μm or less.

Next, as shown in FIG. 2C, the via paste 260 is filled into the through hole 250. The via paste 260 includes copper particles 290, Sn—Bi solder particles 300 containing Sn and Bi, and a thermosetting resin component (organic component) 310 such as an epoxy resin (see FIG. 5A).

Although the filling method of the via paste 260 is not particularly limited, for example, a method such as screen printing is used.

Next, as shown in FIG. 2D, by peeling off the protective film 240 from the surface of the uncured base material 230, a part of the via paste 260 is protruded from the through hole 250 (see FIG. 2B) as a protruding portion 270. A substrate 500 is manufactured. Although the height h of the protrusion 270 depends on the thickness of the protective film, it is preferably 0.5 μm or more and 50 μm or less, and more preferably 1 μm or more and 30 μm or less. If the protruding portion 270 is too high, the paste may overflow around the through-hole 250 on the surface of the uncured base material 230 in the pressurizing step described later, and the surface smoothness may be lost. In addition, when the protruding portion 270 is too low, pressure may not be sufficiently applied to the via paste filled in the pressurizing process described later.

Next, as shown in FIG. 3A, the metal foil 150 is placed on the uncured base material 230 and pressed in the direction indicated by the arrow 280. At the time of pressurization, a force is applied to the protruding portion 270 via the metal foil 150, so that the via paste 260 filled in the through hole 250 is compressed with a high pressure.

Since the incompressible member 220 is used as a part of the uncured base material 230, the diameter of the through hole 250 does not widen and is strong against the via paste 260 at the time of pressurization (further heating) indicated by an arrow 280. Pressure is applied. As a result, the distance between the copper particles and the Sn—Bi particles contained in the via paste 260 is reduced, and they are in close contact with each other. Therefore, the ratio of the resin part in the via paste 260 is reduced. In other words, the ratio of the metal part in the via paste 260 increases.

Then, by heating while maintaining the compressed state, an alloying reaction occurs, and a metal portion 190 and a resin portion 200 (see FIG. 1B) are formed. Moreover, the thermosetting resin component 310 becomes the resin part 200 by thermosetting, and the via-hole conductor 140 is formed (see FIG. 1B). Through the above steps, the uncured base material 230 becomes the electrically insulating base material 130 as shown in FIG. 3B. Here, the metal portion 190 has a first metal region 160 mainly composed of copper, a second metal region 170 mainly composed of tin-copper alloy, and a third metal region 180 mainly composed of bismuth. (See FIG. 1B).

In this alloying reaction, the size (or volume% or weight%) of the second metal region 170 is made larger than the size (or volume% or weight%) of the first metal region 160. Further, the size (or volume% or weight%) of the second metal region 170 is made larger than the size (or volume% or weight%) of the third metal region 180. As a result, the reliability of the via-hole conductor 140 increases and the strength increases.

In addition, the reliability of the via-hole conductor 140 can be improved by interposing the first metal region 160 and the third metal region 180 in the second metal region 170 without being in contact with each other.

The second metal region 170 includes an intermetallic compound Cu ₆ Sn ₅ and an intermetallic compound Cu ₃ Sn, and a ratio of Cu ₆ Sn ₅ / Cu ₃ Sn is set to 0.001 or more and 0.100 or less. The reliability of the via-hole conductor 140 can be improved.

Although the pressurizing conditions are not particularly limited, it is preferable to set the mold temperature from room temperature (20 ° C.) to a temperature below the melting point of the Sn—Bi solder particles. Moreover, in this pressurization process, in order to advance hardening of the thermosetting contact bonding layer 210, you may use the heating press heated to the temperature required in order to advance hardening.

Next, a photoresist film is formed on the surface of the metal foil 150. Then, the photoresist film is exposed through a photomask. Thereafter, development and rinsing are performed, and a photoresist film is selectively formed on the surface of the metal foil 150. Then, the metal foil 150 not covered with the photoresist film is removed by etching. Thereafter, the photoresist film is removed. In this way, the wiring 120a (first wiring) and the wiring 120b (second wiring) are formed, and the wiring substrate 600 is obtained. For the formation of the photoresist film, a liquid resist or a dry film may be used.

4A to 4C are cross-sectional views illustrating a method for further multilayering the wiring board 600 manufactured in FIG. 3C.

As shown in FIG. 4A, the substrate 500 (see FIG. 2D) having the protrusions 270 is disposed on both sides of the wiring substrate 600 manufactured in FIG. 3C. And a laminated body as shown to FIG. 4B is obtained by pinching | interposing into a press metal mold | die (not shown) through the metal foil 150, and pressurizing and heating. Thereafter, as shown in FIG. 4C, the metal foil 150 is patterned to form an upper layer wiring 121a and a lower layer wiring 121b, thereby forming the multilayer wiring substrate 111.

Through the above steps, the multilayer wiring board 111 in which the upper wiring 121a and the lower wiring 121b are connected via the via-hole conductor 140 is obtained. By further multilayering the multilayer wiring board 111, a multilayer wiring board 110 to which a plurality of wirings as shown in FIG. 1A are connected is obtained.

Next, the manner in which the organic components contained in the via paste 260 are discharged from the via paste 260 will be described with reference to FIGS. 5A and 5B. As the proportion of the organic component contained in the via paste 260 decreases, the proportion of the metal component increases. As a result, the alloying reaction and further the intermetallic compound formation reaction are completed in a short time.

FIGS. 5A and 5B are schematic cross-sectional views before and after compression around the through hole 250 of the uncured base material 230 filled with the via paste 260. FIG. 5A shows before compression, and FIG. 5B shows after compression. FIG. 5A corresponds to an enlarged view of the via paste 260 in FIG. 3A.

The average particle diameter of the copper particles 290 is preferably 0.1 μm or more and 20 μm or less, and more preferably 1 μm or more and 10 μm or less. When the average particle size of the copper particles 290 is too small, the tap density (JIS X 2512) of the copper particles 290 is reduced, so that the via paste having the copper particles 290 in the through holes 250 (see FIG. 2B) is high. It tends to be difficult to fill and expensive. On the other hand, when the average particle diameter of the copper particles 290 is too large, when the via-hole conductor 140 having a diameter as small as 100 μm or less, more preferably 80 μm or less is to be formed, it tends to be difficult to fill.

As the particle shape of the copper particles 290, for example, a spherical shape, a flat shape, a polygonal shape, a scale shape, a flake shape, or a shape having protrusions on the surface is used, but the particle shape is not limited thereto. Moreover, a primary particle may be sufficient and the secondary particle may be formed.

The Sn-Bi solder particles 300 mean solder particles 300 containing Sn and Bi.

Further, by adding indium (In), silver (Ag), zinc (Zn) or the like to the solder particles 300, wettability, fluidity, and the like may be improved. The Bi content in the Sn—Bi solder particles 300 is preferably 10% or more and 58% or less, more preferably 20% or more and 58% or less. The melting point (eutectic point) is preferably 75 ° C. or higher and 160 ° C. or lower, more preferably 135 ° C. or higher and 150 ° C. or lower. As the Sn—Bi solder particles 300, two or more types of particles having different compositions may be used in combination. Among these, Sn-58Bi solder particles 300, which are lead-free solder having a low eutectic point of 138 ° C., are particularly preferable from the viewpoint of the environment.

The average particle size of the Sn—Bi solder particles 300 is preferably 0.1 μm or more and 20 μm or less, more preferably 2 μm or more and 15 μm or less. When the average particle size of the Sn—Bi solder particles is too small, the specific surface area becomes large and the ratio of the oxide film on the surface becomes large, so that it becomes difficult to melt. On the other hand, when the average particle size of the Sn—Bi solder particles is too large, the via paste 260 to the through hole 250 is difficult to fill.

As the thermosetting resin component 310, for example, glycidyl ether type epoxy resin, alicyclic epoxy resin, glycidyl amine type epoxy resin, glycidyl ester type epoxy resin, or other modified epoxy resins are used.

Moreover, the thermosetting resin component 310 may contain a curing agent. Although the kind of hardening | curing agent is not specifically limited, It is preferable to use the hardening | curing agent containing the amine compound which has at least 1 or more hydroxyl group in a molecule | numerator. Such a curing agent acts as a curing catalyst for the epoxy resin and reduces the contact resistance at the time of bonding by reducing the copper film and the oxide film present on the surface of the Sn—Bi solder particles 300. . In particular, an amine compound having a boiling point higher than the melting point of the Sn—Bi solder particles is preferable because the contact resistance during bonding is reduced.

Examples of such amine compounds include 2-methylaminoethanol, N, N-diethylethanolamine, N, N-dibutylethanolamine, N-methylethanolamine, N-methyldiethanolamine, N-ethylethanolamine, N -Butylethanolamine, diisopropanolamine, N, N-diethylisopropanolamine, 2,2'-dimethylaminoethanol, triethanolamine and the like.

Via paste 260 is obtained by mixing copper particles 290, Sn—Bi solder particles 300 containing Sn and Bi, and a thermosetting resin component 310 such as an epoxy resin. Specifically, for example, it is obtained by adding copper particles and Sn—Bi solder particles to a resin varnish containing an epoxy resin, a curing agent and a predetermined amount of an organic solvent, and mixing them with a planetary mixer or the like.

The ratio of the thermosetting resin component 310 in the via paste 260 is 0.3% by mass or more and 30% by mass or less, and more preferably 3% by mass or more and 20% by mass or less in order to obtain a low resistance value. In addition, it is preferable from the viewpoint of securing sufficient workability.

In addition, as a mixing ratio of the copper particles 290 in the via paste 260 and the Sn—Bi solder particles 300, the weight ratio of Cu, Sn, and Bi in the paste is shown in a triangular diagram as shown in FIG. , A, B, C, and D are preferably included so as to be in a region surrounded by a quadrangle having apexes. For example, when the Sn-58Bi solder particles 300 are used as the Sn-Bi solder particles 300, the content ratio of the copper particles 290 with respect to the total amount of the copper particles 290 and the Sn-58Bi solder particles 300 is: It is preferable that they are 22 mass% or more and 80 mass% or less, Furthermore, they are 40 mass% or more and 80 mass% or less.

As shown in FIG. 5A, the protruding portion 270 protruding from the through hole 250 formed in the uncured base material 230 is pressed through the metal foil 150 as indicated by an arrow 280a. Then, as shown in FIG. 5B, the via paste 260 filled in the through hole 250 (see FIG. 2B) is compressed. At this time, a considerable portion of the thermosetting resin component 310 in the via paste 260 is pushed out of the through hole 250 as indicated by an arrow 280b. Thereafter, the copper particles 290 and the Sn—Bi solder particles 300 are alloyed by heating, and the metal portion after alloying becomes 74 vol% or more, 80 vol% or more, and further 90 vol% or more in the via-hole conductor.

When the via paste 260 is filled, pressurized, and heated, the incompressible member 220 is formed so that the through hole 250 (see FIG. 2B) is less likely to spread or deform under pressure from the via paste 260. Is used.

Next, a mechanism for reducing organic components in the via paste 260 will be described with reference to FIGS.

FIG. 6 is a schematic diagram showing the state of via paste when a member having compressibility is used as the electrically insulating substrate. As the compressible member 340, for example, a prepreg in which glass fiber, aramid fiber, or the like is used as the core material 320 and the core material 320 is impregnated with a semi-cured resin 330 made of epoxy resin or the like is used. The prepreg exhibits compressibility due to the presence of a gap between the fibers of the core material, a gap between the core material and the semi-cured resin, or voids (for example, air bubbles) contained in the semi-cured resin. That is, the cured product of prepreg is incompressible, but prepreg has compressibility. This is because when the prepreg is heated and compressed, the resin in a semi-cured state softens and fills the gaps between the fibers of the core material, the core material and the resin, or the voids contained in the resin (for example, air bubbles). It is.

Since the compressible member 340 has bubbles (or voids) or the like inside, when compressed, its thickness is compressed by about 10% to 30%.

When a compressive member 340 is formed with a through-hole serving as a via, filled with via paste, provided with a protrusion, and then pressurized, the diameter (or cross-sectional area) of the pressurized through-hole is Compared to 10% to 20%.

This is because part of the glass fiber is cut when the through hole is formed. That is, when a prepreg having a woven fabric or a nonwoven fabric as a core material is used, there are cases where sufficient pressure and compression cannot be performed.

In FIG. 6, an arrow 280c indicates a state in which the diameter of the through hole 250 is increased (or the diameter of the through hole 250 is expanded or deformed) when the via paste 260 is compressed and compressed as indicated by an arrow 280a. ing.

When the compressible member 340 as shown in FIG. 6 is used, a pressure as shown by an arrow 280a in FIG. 6 is applied to the via paste 260, and the diameter of the through hole 250 (see FIG. 2B) is increased by the pressure shown by the arrow 280c. The via paste 260 expands by a volume corresponding to the volume of the protruding portion 270. Therefore, even if the pressure indicated by the arrow 280a is increased, it is difficult to compress and compress the via paste 260. As a result, it becomes difficult to move the thermosetting resin component 310 in the via paste 260 into the uncured substrate 230 (see FIG. 5A). Therefore, the ratio of the volume fraction of the thermosetting resin component 310 in the via paste 260 hardly changes before and after pressurization with the arrow 280a.

It is known that the volume fraction when the sphere is irregularly placed in the container is about 64% at maximum as “random fine packing” (for example, Nature 435, 7195 (May 2008), Song et al.).

As described above, when the compressible member 340 is used as the electrically insulating base material, the filling density (and the volume fraction) of the copper particles 290 and the solder particles 300 contained in the via paste 260 is increased. From the viewpoint of random fine packing, it is difficult to increase the volume fraction. Therefore, even if the protrusions 270 are pressurized and compressed to such an extent that the copper particles 290 and the solder particles 300 are deformed and brought into surface contact with each other, the thermosetting remaining in the gaps between the plurality of copper particles 290 and the plurality of solder particles 300 It is difficult to drive the conductive resin component 310 out of the via paste 260.

As a result, the state shown in FIGS. 14 to 16B is obtained, and even if the pressure is increased, it is difficult to make the volume fraction of the metal portion 190 in the via-hole conductor 140 higher than 70 vol%.

As described above, in the compressible member 340, the diameter of the through hole 250 is expanded or deformed by the pressure from the via paste 260. Therefore, the via paste 260 may not be sufficiently compressed even when a high pressure is applied.

On the other hand, when an incompressible member (for example, a film base material) is used, a through hole to be a via is formed in the thermosetting adhesive layer incompressible member, a via paste is filled, a protrusion is provided, and then pressurization is performed. However, the diameter (or cross-sectional area) of the through hole after pressurization hardly changes compared with that before pressurization. Alternatively, the amount of change is suppressed to less than 3%. And since the diameter and cross-sectional area of the through hole do not change before and after filling the via paste, the via paste can be sufficiently compressed without using special equipment. This is because in the case of an incompressible member, even if the through hole cuts a part of the incompressible member, the incompressible member is hardly unwound or spreads.

However, even when a heat-resistant film such as a polyimide film is used, if the thickness is as thick as 70 μm, the via paste 260 may not be sufficiently compressed even when a high pressure is applied using the protrusions 270.

7 and 8 are schematic views showing the state of the via paste when an incompressible member is used.

By using an incompressible member 220 such as a heat-resistant film as the uncured base material 230, the flow component of the thermosetting resin component 310 in the via paste 260 (for example, an insulating component such as an organic component) is transferred to the via-hole conductor 140. Can be kicked out of. As a result, the volume fraction of the thermosetting resin component 310 in the via paste 260 can be reduced.

As shown in FIGS. 7 and 8, the diameter of the through hole 250 (see FIG. 2B) hardly expands even when a pressure as indicated by an arrow 280 a is applied to the via paste 260. As a result, as the pressure indicated by the arrow 280a increases, the copper particles 290 and the solder particles 300 contained in the via paste 260 come into surface contact with each other over a wider area while deforming each other. Therefore, the volume fraction of the metal part 190 in the via-hole conductor 140 can be higher than 70 vol%, more preferably 80 vol% or higher and 90 vol% or higher.

Note that it is preferable that the hardness of the copper particles 290 and the solder particles 300 be different in order to bring the copper particles 290 and the solder particles 300 into surface contact with each other over a wider area while deforming each other. For example, by reducing the hardness of the solder particles 300 as compared with the hardness of the copper particles 290, the slip (or slip) between the powders can be reduced. As a result, during the pressure compression shown in FIGS. 7 and 8, the solder particles 300 are deformed while maintaining a state of being sandwiched between the plurality of copper particles 290, and the flow components (for example, Insulating components such as organic components) can be driven out of the via-hole conductor 140. As a result, the volume fraction of the thermosetting resin component 310 in the via paste 260 can be further reduced.

As shown in FIG. 7 described above, when the via paste 260 is pressurized and compressed from the outside of the metal foil 150 as indicated by an arrow 280a, the fluid component in the via paste 260, that is, the thermosetting resin component 310 is not It flows out to the thermosetting adhesive layer 210 provided on the surface of the compressible member 220. As a result, as shown in FIG. 8, the filling rate of the copper particles 290 and the solder particles 300 in the via paste 260 is increased. 7 and 8, the state in which the copper particles 290 and the solder particles 300 are compressed, deformed, and brought into surface contact with each other is not shown. Further, the protruding portion 270 formed by the via paste 260 formed on the metal foil 150 is not shown.

In FIG. 8, the pressure (arrow 280 c) due to the thermosetting resin component 310 in the via paste 260 exceeds the pressure (arrow 280 d) from the thermosetting adhesive layer 210, and the thermosetting resin component 310 is in the through hole 250. It shows how it flows out. By using the incompressible member 220, the thermosetting resin component 310 in the via paste 260 can be discharged out of the via paste 260, and the volume fraction of the thermosetting resin component 310 in the via paste 260. Can be greatly reduced. The volume fraction of metal components such as copper particles 290 and solder particles 300 in the via paste 260 is increased by the amount of the thermosetting resin component 310 contained in the via paste 260. As a result, the volume fraction of the metal portion 190 in the via-hole conductor 140 (see FIGS. 1B and 9B) can be increased to 74 vol% or more.

That is, by using an incompressible base material for the uncured base material 230, the diameter of the through hole 250 is hardly changed before and after the compression, so that the via paste 260 can be highly compressed according to the protrusion of the via paste 260. .

Note that the difference in diameter (or cross-sectional area) of the through-holes before and after pressurization is preferably less than 3%, and more preferably less than 2%.

Thus, in the present embodiment, the volume fraction of the metal part 190 after alloying composed of the copper particles 290 and the solder particles 300 can be set to 74.0 vol% or more and 99.5 vol% or less. Further, in the via-hole conductor 140 that electrically connects a plurality of wirings, the volume fraction of the resin part 200, which is a part excluding the metal part 190, can be reduced to 0.5 vol% or more and 26.0 vol% or less. . Here, the resin portion 200 may be a resin portion included in the via-hole conductor 140, and may not be the thermosetting resin component 310 included in the via paste 260. Further, the thermosetting resin component 310 and the thermosetting adhesive layer 210 in the via paste 260 may be compatible with each other or may be melted together.

In this way, the via paste 260 is filled in the through-holes 250 formed in the incompressible member 220 and the thermosetting adhesive layer 210 and is pressurized, whereby the content of the thermosetting resin component 310 in the via paste ( Alternatively, the volume fraction) can be further reduced. Therefore, the filling rate (or volume fraction) of copper particles 290, solder particles 300, etc. in via paste 260 can be increased. As a result, the contact area between the copper particles 290 and the solder particles 300 increases, the alloying reaction is promoted, and the proportion of the metal portion in the via-hole conductor 140 can be increased.

Next, how the alloying reaction between copper particles and solder particles is promoted by reducing the volume fraction of the thermosetting resin component 310 will be described.

FIG. 9A is a schematic diagram showing the state of the via paste before the alloying reaction. FIG. 9B is a schematic diagram showing a state of the via-hole conductor after the alloying reaction.

9A, the copper particles 290 and the solder particles 300 are compressed with each other and packed with high density as indicated by an arrow 280. At this time, it is desirable that the copper particles 290 and the solder particles 300 are deformed and in surface contact with each other. As the area where the copper particles 290 and the solder particles 300 are in contact with each other is wider, the alloying reaction between the copper particles 290 and the solder particles 300 (and the intermetallic compound formation reaction) proceeds more uniformly in a shorter time. .

In addition, the volume fraction of the thermosetting resin component 310 contained in the via paste 260 is 0.5 vol% or more and 26 vol% or less (further 20 vol% or less, and further 10 vol% or less).

As shown in FIG. 9A, the metal paste 150 is pressure-bonded to the uncured base material 230, and a predetermined pressure is applied to the protruding portion 270 of the via paste 260 through the metal foil 150, whereby the via paste 260 is pressurized and compressed. By doing so, the copper particles 290 or the copper particles 290 and the solder particles 300 can be in surface contact with each other, and the alloying reaction is promoted.

Projections 270 are formed on the upper and lower surfaces of the via paste 260 in FIG. 9A. Further, the upper and lower surfaces of the via-hole conductor 140 in FIG. 9B are flat with no protrusions. Thus, it is desirable that the upper and lower surfaces of the via paste 260 become flat after the alloying reaction. Conventionally, when an incompressible member is used, the protruding portion of the via-hole conductor may remain even after the alloying reaction, making it difficult to mount the component. However, by making the alloying reaction proceed very fast as in the present embodiment, the volume fraction of the metal portion 190 in the via-hole conductor 140 can be made 74.0 vol% or more and the via-hole conductor can be made flat. . Further, the volume fraction of the resin portion 200 in the via-hole conductor 140 can be set to 26.0 vol% or less. The height of the protrusion 270 (h in FIG. 2D) is desirably 2 μm or more, more preferably 5 μm or more, or 0.5 times or more of the thickness of the metal foil 150. When the size of the protrusion 270 is smaller than 2 μm, or smaller than 0.5 times the thickness of the metal foil 150, copper is used even when an incompressible member is used for the electrically insulating base material 130. The volume fraction in the via paste 260 such as the particles 290 and the solder particles 300 may not be 74 vol% or more.

Note that the particle diameters of the copper particles 290 and the solder particles 300 may be different from each other, or the copper particles 290 having different particle diameters may be mixed. However, in such a case, the specific surface area of the powder is increased and the viscosity of the via paste 260 is increased. As a result, even if the total volume fraction of the copper particles 290 and the solder particles 300 in the via paste 260 can be increased, the viscosity of the via paste 260 increases and affects the filling property to the through holes 250. There is a case. Therefore, it is preferable that the copper particles 290 and the solder particles 300 have the same particle size.

In order to deform and bring the copper particles 290 and the solder particles 300 into surface contact with each other, it is desirable to compress and compress the copper particles 290 or until the solder particles 300 and the copper particles 290 are plastically deformed.

As shown by arrows 280 in FIGS. 9A and 9B, it is preferable that a part of the Sn—Bi solder particles 300 is melted by heating at a predetermined temperature while maintaining the crimped state. By heating in the pressurizing process, the total time of the pressurizing process and the heating process can be shortened, and productivity is increased.

FIG. 9B shows a state after the copper particles 290 deformed and in surface contact with each other and the solder particles 300 undergo an alloying reaction (and further an intermetallic compound formation reaction). The via-hole conductor 140 has a metal portion 190 and a resin portion 200. The metal portion 190 has a first metal region 160 mainly composed of copper, a second metal region 170 mainly composed of a tin-copper alloy, and a third metal region 180 mainly composed of bismuth. The metal part 190 and the resin part 200 constitute a via-hole conductor 140.

In this way, the via-hole conductor 140 is formed as shown in FIG. 9B. The resin portion 200 is a cured resin including an epoxy resin. Second metal region 170 has a larger cross-sectional area, volume fraction, or weight fraction than first metal region 160. Furthermore, the second metal region 170 has a larger cross-sectional area, volume fraction, or weight fraction than the third metal region 180.

In addition, the metal foils 150 forming the plurality of wirings 120 are electrically connected via the second metal region 170. The first metal region 160 and the third metal region 180 are scattered in the second metal region 170 without being in contact with each other, so that the reliability of the via-hole conductor 140 is increased. Furthermore, the second metal region 170 includes an intermetallic compound Cu ₆ Sn ₅ and an intermetallic compound Cu ₃ Sn, and a ratio of Cu ₆ Sn ₅ / Cu ₃ Sn is set to 0.001 or more and 0.100 or less. The reliability of the via-hole conductor 140 is increased.

Also, while the alloying reaction is taking place, the height of the protruding portion 270 of the metal foil 150 after alloying can be lowered by continuing the pressure compression indicated by the arrow 280. By reducing the height of the protruding portion 270 before the alloying reaction after the alloying reaction, the volume fraction of the resin portion 200 occupying the via-hole conductor 140 can be reduced, and the variation in the thickness of the multilayer wiring board 110 can be reduced. Moreover, since the planarity and smoothness of the multilayer wiring board 110 can be improved, the mounting property of a bare chip such as a semiconductor chip is improved.

In the via-hole conductor 140 formed by the reaction between the copper particles 290 and the solder particles 300, the second metal region 170 includes the intermetallic compound Cu ₆ Sn ₅ and the intermetallic compound Cu ₃ Sn. Here, by suppressing the ratio of Cu ₆ Sn ₅ / Cu ₃ Sn to 0.001 or more and 0.100 or less, for example, generation of voids 5a (see FIG. 14) such as Kirkendyl voids can be suppressed.

In order for the ratio of Cu ₆ Sn ₅ / Cu ₃ Sn to be 0.001 or more and 0.100 or less, it is desirable that the contact area between the copper particles 290 and the solder particles 300 is wide. At the time of performing the alloying reaction (or intermetallic compound formation reaction), the volume fraction of the thermosetting resin component 310 in the via paste 260 is 26 vol% or less (more 20 vol% or less, and further 10 vol% or less). Is desirable. The smaller the volume fraction of the thermosetting resin component 310 is, the larger the contact area between the copper particles 290 and the solder particles 300 becomes, and the alloying reaction becomes uniform. As a result, in the second metal region including the intermetallic compound _Cu 6 Sn ₅ intermetallic compound _Cu 3 _Sn, the ratio of _Cu ₆ Sn 5 / Cu 3 Sn can be suppressed to 0.100.

As described above, by using an incompressible member as the uncured base material 230, the density of the copper particles 290 and the Sn—Bi solder particles 300 filled in the through holes 250 is increased.

In addition, while maintaining the compression, the compressed via paste 260 is heated to a Sn-Bi solder particle 300 temperature range from the eutectic temperature of the Sn-Bi solder particles 300 to a temperature not higher than the eutectic temperature by 10 ° C. It is useful to melt a part of the Bi-based solder particles 300 and subsequently heat it to a temperature range of 20 ° C. to 300 ° C. higher than the eutectic temperature. The growth of the second metal region 170 can be promoted by such pressurization and heating. Furthermore, it is preferable to carry out these in one step with continuous pressure bonding and heating. By performing the process in one continuous process, the formation reaction of each metal region can be further stabilized, and the structure of the via itself can be stabilized.

For example, in FIG. 9A, high compression is performed so that the volume fraction of the copper particles 290 and the solder particles 300 in the via paste 260 becomes 74 vol% or more. In this state, the via paste 260 is gradually heated to a temperature equal to or higher than the eutectic temperature of the Sn—Bi solder particles 300. By this heating, a part of the Sn—Bi solder particles 300 melts at a composition ratio that melts at that temperature. Then, a second metal region 170 mainly composed of tin or a tin-copper alloy is formed on or around the copper particles 290. In this case, the surface contact portion where the copper particles 290 are in surface contact may also be changed to a part of the second metal region 170. When the copper particles 290 and the molten Sn—Bi solder particles 300 are in surface contact with each other in a deformed state, Sn in the Sn—Bi solder particles 300 reacts with Cu in the copper particles 290. Thus, a Sn—Cu compound layer (intermetallic compound) containing Cu ₆ Sn ₅ or Cu ₃ Sn and a second metal region 170 mainly composed of a tin-copper alloy are formed. On the other hand, the Sn—Bi-based solder particles 300 continue to maintain a molten state while being supplemented with Sn from the internal Sn phase, and the remaining Bi precipitates, whereby the third metal region 180 containing Bi as a main component is obtained. Is formed. As a result, a via-hole conductor 140 having a structure as shown in FIG. 9B is obtained.

In FIG. 9B, the total weight ratio of the first metal region 160 and the second metal region 170 to the entire via-hole conductor 140 is preferably in the range of 20% to 90%. When the total weight ratio is less than 20%, the via resistance may increase or a predetermined compressed state may not be obtained. Moreover, it may be technically difficult to exceed 90%.

Then, when heating is performed in this state and the eutectic temperature of the Sn-Bi solder particles 300 is reached, the Sn-Bi solder particles 300 start to partially melt. The composition of the solder to be melted is determined by the temperature, and Sn that is difficult to melt at the temperature at the time of heating remains as an Sn solid phase body. Further, when the copper particles 290 come into contact with the molten solder and the surface is wetted with the molten Sn—Bi-based solder, Cu and Sn interdiffusion proceeds at the interface of the wet portion, and the Sn—Cu compound layer Etc. are formed. In this way, the proportion of the second metal region 170 in the via-hole conductor 140 can be made larger than that of the first metal region 160 and larger than that of the third metal region 180.

On the other hand, Sn in the molten solder decreases due to the further progress of the formation of the Sn—Cu compound layer and the like and the mutual diffusion. Since the decreased Sn in the molten solder is compensated from the Sn solid layer, the molten state continues to be maintained. Further, when Sn decreases and the ratio of Sn and Bi becomes larger than that of Sn-58Bi, Bi begins to segregate, and the third metal region 180 is formed as a solid phase body containing bismuth as a main component.

Note that well-known solder materials that melt at a relatively low temperature range include Sn—Pb solder, Sn—In solder, and Sn—Bi solder. Of these materials, In is expensive and Pb is considered to have a high environmental load. On the other hand, the melting point of Sn—Bi solder is 140 ° C. or lower, which is lower than the general solder reflow temperature when electronic components are surface-mounted. Therefore, when only Sn—Bi solder is used as a via hole conductor of a circuit board as a single unit, the via resistance may fluctuate due to remelting of the solder of the via hole conductor during solder reflow.

FIG. 10 is a triangular diagram showing an example of the metal composition in the via paste of this embodiment. As shown in FIG. 10, the metal composition in the via paste of the present embodiment is represented by the weight composition ratio (Cu: Sn: Bi) of Cu, Sn, and Bi as A (0.37: 0.567: 0.063), B (0.22: 0.3276: 0.4524), C (0.79: 0.09: 0.12), D (0.89: 0.10: 0.01) It is desirable that the region be surrounded by a quadrangle as a vertex.

More desirably, C (0.79: 0.09: 0.12), D (0.89: 0.10: 0.01), E (0.733: 0.240: 0.027), F It is desirable that the region be surrounded by a quadrangle having (0.564: 0.183: 0.253) as a vertex. C (0.79: 0.09: 0.12), D (0.89: 0.10: 0.01), E (0.733: 0.240: 0.027), F (0.564) : 0.183: 0.253), the via resistance can be reduced by making the area surrounded by a quadrangle. In the second metal region, the intermetallic compound Cu ₆ Sn ₅ and the intermetallic compound Cu ₃ Sn are included, and the ratio of Cu ₆ Sn ₅ / Cu ₃ Sn can be easily set to 0.100 or less.

When a via paste having such a metal composition is used, the composition of the Sn—Bi solder particles 300 is higher than that of the eutectic Sn—Bi solder composition (Bi 58% or less, Sn 42% or more). . By using such a via paste, a part of the solder composition melts in a temperature range of 10 ° C. or higher from the eutectic temperature of the Sn—Bi solder particles, while Sn that does not melt remains. However, the remaining Sn diffuses and reacts on the copper particle surface. As a result, the Sn concentration decreases from the Sn—Bi solder particles 300, so that the remaining Sn melts. On the other hand, Sn is melted even when the temperature rises by continuing to heat, and Sn that could not be melted in the solder composition disappears. Further, by continuing the heating, the reaction with the surface of the copper particles proceeds, whereby bismuth. The third metal region 180 is formed as a solid phase body mainly composed of. And by making the 3rd metal area | region 180 precipitate and exist in this way, it becomes difficult to remelt the solder of a via-hole conductor at the time of solder reflow. Further, by using the Sn-Bi composition solder particles 300 having a large Sn composition, the Bi phase remaining in the via can be reduced, so that the resistance value can be stabilized and the resistance can be improved even after the solder reflow. Value fluctuations are less likely to occur.

The temperature at which the compressed via paste 260 is heated is not less than the eutectic temperature of the Sn—Bi solder particles 300 and is not particularly limited as long as it does not decompose the components of the uncured base material 230. Not. Specifically, when Sn-58Bi solder particles having a eutectic temperature of 139 ° C. are used as the Sn—Bi based solder particles, the Sn-58Bi solder particles 300 are first heated to a temperature range of 139 ° C. to 149 ° C. It is preferable to further heat gradually to a temperature range of about 159 ° C. to 230 ° C. In addition, the thermosetting resin component contained in the via paste 260 is cured by appropriately selecting the temperature.

Next, the present embodiment will be specifically described using examples. Note that the scope of this embodiment is not limited by the contents of this example. First, the raw materials used in this example will be described below.

Copper particles (copper particles 290): 1100Y manufactured by Mitsui Kinzoku Co., Ltd. having an average particle diameter of 5 μm
-Sn-Bi solder particles (solder particles 300): Powdered by the composition and melted so as to have the solder composition shown in (Table 1) by composition, and spheroidized to an average particle size of 5 μm I use what I did.
Epoxy resin (thermosetting resin component 310): Japan Epoxy Resin Co., Ltd. jeR871
Curing agent: 2-methylaminoethanol, boiling point 160 ° C., manufactured by Nippon Emulsifier Co., Ltd. Resin sheet (uncured base material 230): polyimide film (non-compressible member 220 of length 500 mm × width 500 mm, thickness 10 μm to 50 μm) ), An uncured epoxy resin layer (thermosetting adhesive layer 210) having a thickness of 10 μm is formed.
Protective film (protective film 240): PET sheet having a thickness of 25 μm Copper foil (metal foil 150): thickness of 25 μm

(Preparation of via paste)
A via paste was prepared by blending the metal components of the copper particles and Sn-Bi solder particles described in (Table 1), the epoxy resin and the resin component of the curing agent, and mixing them with a planetary mixer. ing. The blending ratio of the resin component is 10 parts by weight of epoxy resin and 2 parts by weight of curing agent with respect to 100 parts by weight of the total of copper particles and Sn—Bi solder particles.

(Manufacture of multilayer wiring boards)
A protective film is bonded to both surfaces of the resin sheet. Then, 100 holes having a diameter of 150 μm are drilled by laser from the outside of the resin sheet to which the protective film is bonded.

Next, fill the through hole with the prepared via paste. And the protrusion part which a part of via paste protruded from the through-hole is formed by peeling the protective film of both surfaces.

Next, copper foil is disposed on both surfaces of the resin sheet so as to cover the protruding portions. And a release paper is installed on the metal mold | die under a heating press machine, a laminated body with the resin sheet by which copper foil is arrange | positioned, and a pressure of 3 MPa is applied. The laminated body is heated from room temperature 25 ° C. to the maximum temperature 220 ° C. in 60 minutes, kept at 220 ° C. for 60 minutes, and then cooled to room temperature over 60 minutes. In this way, a wiring board is obtained.

(Evaluation)
<Resistance test>
The resistance value of 100 via-hole conductors formed on the obtained wiring board is measured by the 4-terminal method. Then, 100 initial resistance values and maximum resistance values are obtained. As the initial resistance value, A is 2 mΩ or less and B is 2 mΩ or more. Further, as the maximum resistance value, A is less than 3 mΩ, and B is greater than 3 mΩ.

Here, the initial resistance value (initial average resistance value) is calculated by forming a daisy chain including 100 vias, measuring the total resistance value of 100 vias, and dividing this by 100. . The maximum resistance value is the maximum value among the average resistance values of the daisy chains formed by forming 100 daisy chains including 100 vias. In Table 1, the resistance value (mΩ) and the specific resistance value (Ω · m) are described.

<Connection reliability>
A heat cycle test of 500 cycles was performed on the wiring substrate whose initial resistance value was measured, and A having a rate of change of 10% or less with respect to the initial resistance value was A and exceeding B was 10%.

The results are shown in (Table 1). Further, FIG. 10 shows a triangular diagram of each composition of the examples and comparative examples shown in (Table 1). In Table 1 and FIG. 10, Examples 1 to 17 are indicated by E1 to E17, and Comparative Examples 1 to 9 are indicated by C1 to C9. In the triangular diagram of FIG. 10, “white circle” indicates the composition of the example, and “black circle” indicates the composition of comparative example 1 (C1) in which the Bi amount relative to the Sn amount is smaller than the metal composition of the example. In addition, “white triangle” is a composition of Comparative Example 7 (C7) in which the Bi amount relative to the Sn amount is larger than the metal composition of the example, and “white square” is a comparison in which the Sn amount relative to the Cu amount is larger than the metal composition of the example. Comparative examples 3, 5, and 8 (C3, C5) in which the composition of Examples 2, 4, 6, and 9 (C2, C4, C6, and C9), “black triangle” has a smaller amount of Sn relative to the amount of Cu than the metal composition of the example , C8).

From FIG. 10, the composition of the example in which A evaluation can be obtained for all the determinations of the initial resistance value, the maximum resistance value, and the connection reliability is that the weight ratio (Cu: Sn: Bi) in the triangular diagram is A (0. 37: 0.567: 0.063), B (0.22: 0.3276: 0.4524), C (0.79: 0.09: 0.12), D (0.89: 0.10) : 0.01) is a range of a region surrounded by a quadrangle. Here, point A indicates Example 2 (E2), point B indicates Example 12 (E12), point C indicates Example 9 (E9), and point D indicates Example 13 (E13).

Furthermore, C (0.79: 0.09: 0.12), D (0.89: 0.10: 0.01), E (0.733: 0.240: 0.027), F (0 .564: 0.183: 0.253), the A evaluation is obtained for all the determinations of the initial resistance value, the maximum resistance value, and the connection reliability. Here, the point E represents Example 14 (E14), and the point F represents Example 17 (E17). Thus, the weight ratio (Cu: Sn: Bi) in the triangular diagram is changed to C (0.79: 0.09: 0.12), D (0.89: 0.10: 0.01), E ( 0.733: 0.240: 0.027) and F (0.564: 0.183: 0.253) as a region surrounded by a quadrangle, the weight of Cu having a lower resistance value By increasing the ratio, the resistance of via holes is reduced. Furthermore, the alloying reaction of Cu and Sn all eliminates Sn-Bi remelting and realizes a highly reliable printed wiring board.

Further, in Comparative Example 7 (C7) in the region having a composition with a large amount of Bi with respect to the amount of Sn plotted by the “white triangle” in FIG. 10, the amount of bismuth precipitated in the via increases. The volume resistivity of Bi is 78 μΩ · cm, the volume resistivity of Cu (1.69 μΩ · cm), the volume resistivity of Sn (12.8 μΩ · cm), and the volume of the compound of Cu and Sn. It is remarkably larger than the resistivity (Cu ₃ Sn: 17.5 μΩ · cm, Cu ₆ Sn ₅ : 8.9 μΩ · cm). Therefore, in consideration of the volume resistivity of these metal materials, it is expected that the volume resistivity increases as the amount of Bi with respect to the amount of Sn increases. Furthermore, there is a possibility that the resistance value may change or the connection reliability may be lowered depending on the presence state or the dotted state of bismuth.

Further, in the regions of Comparative Examples 2, 4, 6, and 9 (C2, C4, C6, and C9) in the region of the composition having a large Sn amount with respect to the Cu amount plotted by the “white square” in FIG. The contact portion is not sufficiently formed. Further, since the Sn—Cu compound layer is formed at the contact portion between the copper particles after mutual diffusion, the initial resistance value and the maximum resistance value are high.

Further, in the composition of Comparative Example 1 (C1) in the region of the composition having a small amount of Bi with respect to the amount of Sn plotted by “black circle” in FIG. 10, the eutectic temperature of the Sn—Bi based solder particles due to the small amount of Bi. The amount of solder that melts around 140 ° C. is reduced. Therefore, the Sn—Cu compound layer that reinforces the surface contact portion between the copper particles is not sufficiently formed, and the connection reliability is lowered. That is, in the case of Comparative Example 1 (C1) using Sn-5Bi solder particles, since the surface contact portion between the copper particles was formed, the initial resistance value and the maximum resistance value were low, but the amount of Bi was small. It is considered that the reaction between Cu and Sn forming the Sn—Cu compound layer that reinforces the surface contact portion did not sufficiently proceed because the solder particles were difficult to melt.

Further, in Comparative Examples 3, 5, and 8 (C3, C5, and C8) of the regions having a small Sn amount with respect to the Cu amount plotted by the “black triangle” in FIG. Since the number of Sn—Cu compound layers formed to reinforce the surface contact portion between the particles is reduced, the connection reliability is lowered.

FIG. 11A and FIG. 12A are electron microscopes of cross sections of via-hole conductors of a multilayer wiring board obtained using the paste according to Example 16 (E16) (copper particles: Sn-28Bi solder weight ratio is 70:30). It is a figure which shows a SEM photograph. Moreover, FIG. 11B and FIG. 12B are those schematic diagrams. 11A and 11B are 3000 times, and FIGS. 12A and 12B are 6000 times.

11A to 12B that the via hole conductor of the present embodiment has a very high metal filling rate. The via-hole conductor 140 includes a resin portion 200 and a metal portion 190. The resin portion 200 is a resin portion containing an epoxy resin. The metal portion 190 includes a first metal region 160 mainly composed of copper, a second metal region 170 mainly composed of a tin-copper alloy, and a third metal region 180 mainly composed of bismuth. Yes. In addition, the size of the second metal region 170 (and also one or more of its volume or weight and cross-sectional area) is larger than the first metal region 160 and larger than the third metal region 180. With this configuration, the plurality of wirings 120 are electrically connected via the second metal region 170. In addition, the first metal region 160 and the third metal region 180 are interspersed in the second metal region 170 without being in contact with each other, so that the alloying reaction (and the intermetallic compound formation reaction) can be performed. It can be performed uniformly without unevenness.

FIG. 13 is a graph showing an example of an analysis result by X-ray diffraction (XRD) of a via-hole conductor. Peak I is Cu (copper). Peak II is Bi (bismuth). Peak III is tin (Sn). Peak IV is the intermetallic compound Cu ₃ Sn. Peak V is the intermetallic compound Cu ₆ Sn ₅ .

FIG. 13 evaluates the influence of the heating temperature (curing temperature) during pressurization on the via-hole conductor, and shows the measurement results at heating temperatures of 25 ° C., 150 ° C., 175 ° C., and 200 ° C. In FIG. 13, the X axis is 2θ (unit is degree), and the Y axis is intensity (unit is arbitrary).

In addition, the sample used for the measurement produced the pellet which consists of via paste, and changed the processing temperature of this pellet. For X-ray diffraction, RINT-2000 manufactured by Rigaku Corporation is used.

From the X-ray diffraction graph of FIG. 13, when the temperature is 25 ° C., the Cu peak I, the Bi peak II, and the Sn peak III are detected, but the Cu ₃ Sn peak IV and the Cu ₆ Sn ₅ No peak V was detected.

When the temperature is 150 ° C., a peak V of Cu ₆ Sn ₅ appears in addition to the peak I of Cu, the peak II of Bi, and the peak III of Sn.

When the temperature is 175 ° C., a peak IV of Cu ₃ Sn appears in addition to a peak I of Cu, a peak II of Bi, and a peak V of Cu ₆ Sn ₅ . In addition, the Sn peak III almost disappears. From the above, it can be seen that the alloying reaction between the Cu particles and the Sn—Bi solder particles, and further the formation reaction of the intermetallic compound proceeded uniformly.

In the graph of FIG. 13 where the sample temperature is 200 ° C., Cu peak I, Bi peak II, and Cu ₃ Sn peak IV are detected, but Sn peak III and Cu ₆ Sn ₅ peak V disappear. ing. From the above, the alloying reaction between Cu particles and Sn—Bi solder particles, and further the formation reaction of intermetallic compounds, the alloying reaction between Cu and Sn—Bi solder particles, and further the reaction of intermetallic compounds Is stabilized by the formation of a Cu ₃ Sn peak IV.

As described above, in the present embodiment, the reliability of the via-hole conductor is increased by making the intermetallic compound not Cu ₆ Sn ₅ but more stable Cu ₃ Sn. In other words, in this embodiment, an alloying reaction (or intermetallic compounding reaction) in which the intermetallic compound is Cu ₃ Sn which is more stable than Cu ₆ Sn ₅ can be performed.

The thickness of the heat resistant film as the incompressible member 220 is desirably 3 μm or more and 55 μm or less, more preferably 50 μm or less, and further 35 μm or less. In addition, when the thickness of the heat resistant film is less than 3 μm, the film strength is lowered and the compression effect of the via paste 260 may not be obtained. Since a heat-resistant film exceeding 55 μm is special and expensive, it is better to use a heat-resistant film having a thickness of 55 μm or less.

The thickness of the thermosetting adhesive layer 210 provided on the surface of the incompressible member 220 is desirably 1 μm or more and 15 μm or less on one side. When it is less than 1 μm, a predetermined adhesion strength may not be obtained. If it exceeds 15 μm, the compression effect of the via paste 260 may not be obtained. In addition, it is useful that the thickness of the incompressible member 220 is thicker than the thickness of the thermosetting adhesive layer 210 on one side.

When the thickness of the incompressible member 220 is 75 μm, the volume fraction of the metal portion 190 occupying in the via-hole conductor 140 may be increased only to about 60 vol% or more and 70 vol% or less.

For example, when the thickness of the incompressible member 220 is 50 μm (when the thermosetting adhesive layer 210 having a thickness of 10 μm is formed on both surfaces, the thickness of the electrically insulating substrate 130 is 70 μm), the via hole conductor 140 occupies it. The volume fraction of the metal part 190 becomes 80 vol% or more and 82 vol% or less.

In the case where the thickness of the incompressible member 220 is 40 μm (when the thermosetting adhesive layer 210 having a thickness of 10 μm is formed on both surfaces, the thickness of the electrically insulating substrate 130 is 60 μm), the metal portion occupied in the via-hole conductor 140 The volume fraction of 190 is 83 vol% or more and 85 vol% or less.

When the thickness of the incompressible member 220 is 30 μm (when the thermosetting adhesive layer 210 having a thickness of 10 μm is formed on both surfaces, the thickness of the electrically insulating substrate 130 is 50 μm), the metal portion occupying the via-hole conductor 140 The volume fraction of 190 is 89 vol% or more and 91 vol% or less.

When the thickness of the incompressible member 220 is 20 μm (when the thermosetting adhesive layer 210 having a thickness of 10 μm is formed on both surfaces, the thickness of the electrically insulating substrate 130 is 40 μm), the metal portion occupying the via-hole conductor 140 The volume fraction of 190 becomes 87 vol% or more and 95 vol% or less.

When the thickness of the incompressible member 220 is 10 μm (when the thermosetting adhesive layer 210 having a thickness of 10 μm is formed on both surfaces, the thickness of the electrically insulating substrate 130 is 30 μm), the metal portion occupied in the via-hole conductor 140 The volume fraction of 190 becomes 98 vol% or more and 99.5 vol% or less.

As described above, the thinner the incompressible member 220 is, the more effective, but the thickness is appropriately selected according to the diameter and density of the via-hole conductor 140, the application, and the like.

From the above, it can be seen that by using the incompressible member 220, the volume fraction of the metal portion 190 occupying in the via-hole conductor 140 increases.

The wiring board of this embodiment is effective for cost reduction, downsizing, high functionality, and high reliability, and is therefore used for mobile phones and the like.

110,111 Multilayer wiring board 120,120a, 120b, 121a, 121b Wiring 130 Electrical insulating base 140 Via hole conductor 150 Metal foil 160 First metal region 170 Second metal region 180 Third metal region 190 Metal portion 200 Resin portion 210 Thermosetting adhesive layer 220 Incompressible member 230 Uncured base material 240 Protective film 250 Through hole 260 Via paste 270 Protrusion 280, 280a, 280b, 280c, 280d Arrow 290 Copper particle 300 Solder particle 310 Thermosetting resin component 320 Core material 330 Semi-cured resin 340 Compressible member 500 Substrate 600 Wiring substrate

Claims

An electrically insulating substrate having an incompressible member and a thermosetting member;
A first wiring and a second wiring formed across the electrically insulating substrate;
A via-hole conductor that penetrates the electrically insulating substrate and electrically connects the first wiring and the second wiring;
The via-hole conductor has a resin portion and a metal portion,
The metal portion includes a first metal region mainly composed of Cu,
A second metal region mainly composed of Sn-Cu alloy;
A third metal region mainly composed of Bi,
The wiring board is larger than the first metal region and larger than the third metal region.
The wiring board according to claim 1, wherein the second metal region covers the first metal region and the third metal region.
The wiring board according to claim 1, wherein the first metal region and the third metal region exist without contacting each other.
2. The wiring board according to claim 1, wherein the second metal region has Cu 6 Sn 5 and Cu 3 Sn, and a ratio of Cu 6 Sn 5 / Cu 3 Sn is 0.001 or more and 0.100 or less.
The weight composition ratio Cu: Sn: Bi of Cu, Sn and Bi in the metal part is represented by A (0.37: 0.567: 0.063), B (0.22: 0.3276) in the triangular diagram. : 0.4524), C (0.79: 0.09: 0.12), and D (0.89: 0.10: 0.01) are in the region surrounded by a quadrangle. Wiring board as described in.
The wiring board according to claim 1, wherein in the via-hole conductor, the metal portion is 74.0 vol% or more and 99.5 vol% or less.
The wiring board according to claim 1, wherein in the via-hole conductor, the resin portion is 0.5 vol% or more and 26.0 vol% or less.
The wiring board according to claim 1, wherein a total weight ratio of the first metal region and the second metal region to the entire via-hole conductor is 20% or more and 90% or less.
The wiring board according to claim 1, wherein the resin portion has a cured product of an epoxy resin.
2. The wiring board according to claim 1, wherein a specific resistance of the via-hole conductor is 1.00 × 10 −7 Ω · m or more and 5.00 × 10 −7 Ω · m or less.
The wiring board according to claim 1, wherein the incompressible member is a film having no space inside.
The wiring board according to claim 1, wherein a thickness of the incompressible member is 3 μm or more and 55 μm or less.
The wiring board according to claim 1, wherein the thermosetting member is an epoxy resin.
The wiring board according to claim 1, wherein the thermosetting member has a thickness of 1 μm or more and 15 μm or less.
Providing a protective film on both sides of a substrate having an incompressible member and an uncured thermosetting member;
Forming a through hole in the base material coated with the protective film by perforating from the outside of the protective film;
Filling the through hole with a via paste having copper particles, solder particles containing tin and bismuth, and a resin;
Peeling the protective film to form a protruding portion from which the via paste protrudes from the through hole; and
Arranging a metal foil on the surface of the base material so as to cover the protruding portion;
Flowing a part of the resin to the base material by applying pressure to the via paste from the metal foil;
Curing the resin by heating the via paste,
A resin part;
A first metal region mainly composed of Cu;
A second metal region mainly composed of Sn-Cu alloy;
A third metal region mainly composed of Bi,
The second metal region is larger than the first metal region and larger than the third metal region;
A metal part,
Forming a via-hole conductor having
Curing the thermosetting member by heating the substrate; and
Forming a wiring by patterning the metal foil;
A method of manufacturing a wiring board comprising:
The method for manufacturing a wiring board according to claim 15, wherein the incompressible member is a film having no space inside.
The method for manufacturing a wiring board according to claim 15, wherein a thickness of the incompressible member is 3 μm or more and 55 μm or less.
The method for manufacturing a wiring board according to claim 15, wherein the thermosetting member is an epoxy resin.
The method for manufacturing a wiring board according to claim 15, wherein a thickness of the thermosetting member is 1 μm or more and 15 μm or less.