Wiring substrate and method of manufacturing the wiring substrate

A wiring substrate includes: a base material; a first through-hole and a second through-hole that are formed in the base material; magnetic material that is filled in the first through-hole; a third through-hole that is formed in the magnetic material; a first plating film that covers an inner wall surface of the third through-hole; and a second plating film that covers an inner wall surface of the second through-hole and the first plating film. The first plating film includes a first electroless plating film that is in contact with the inner wall surface of the third through-hole, and a first electrolytic plating film that is laminated on the first electroless plating film.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2021-001672, filed on Jan. 7, 2021, the entire contents of which are incorporated herein by reference.

FIELD

The embodiment discussed herein is related to a wiring substrate and a method of manufacturing the wiring substrate.

BACKGROUND

Conventionally, there is a wiring substrate having a built-in inductor formed by using a magnetic material. This type of inductor is formed by accommodating the magnetic material in a through-hole in, for example, an insulating resin layer of the wiring substrate and providing a plating film on an inner wall of a through-hole drilled in the magnetic material. In general, a process of providing the plating film on the inner wall of the through-hole in the magnetic material is performed at the same time as the plating film is provided on a surface of the wiring substrate by performing, for example electrolytic copper plating.

However, with the wiring substrate described above, there is a problem in that it is difficult to provide a plating film having a sufficient film thickness on the inner wall of the through-hole in the magnetic material and the electric characteristics of the inductor is not accordingly improved. Specifically, in a process of providing the plating film, an electrolytic plating solution is less likely to flow in the through-hole in the magnetic material as compared to the surface of the wiring substrate, so that the electrolytic plating film is hardly deposited. As a result, the thickness of the plating film provided on the through-hole inner wall of the magnetic material tends to be thinner than the thickness of the plating film provided on the surface of the wiring substrate. Furthermore, if the plating film on the inner wall of the through-hole in the magnetic material is thin, the electric resistance of the plating film is not sufficiently decreased, the improvement of the electric characteristics as the inductor is limited.

Furthermore, in order to thicken the plating film of the through-hole inner wall of the magnetic material, if a period of time for which electrolytic plating is performed is extended or if a current value used by electrolytic plating is increased, the thickness of the plating film of the through-hole inner wall of the magnetic material is increased and, at the same time, the thickness of the plating film of the surface of the wiring substrate is also increased. If the thickness of the plating film is increased more than necessary on the wiring substrate surface, it is difficult to form a minute high-density wiring layer on the wiring substrate surface. Therefore, it is not preferable to thicken the plating film of the through-hole inner wall of the magnetic material by extending the period of time for which electrolytic plating is performed or increasing the current value without careful consideration.

SUMMARY

According to an aspect of an embodiment, a wiring substrate includes: a base material; a first through-hole and a second through-hole that are formed in the base material; a magnetic material that is filled in the first through-hole; a third through-hole that is formed in the magnetic material; a first plating film that covers an inner wall surface of the third through-hole; and a second plating film that covers an inner wall surface of the second through-hole and the first plating film. The first plating film includes a first electroless plating film that is in contact with the inner wall surface of the third through-hole, and a first electrolytic plating film that is laminated on the first electroless plating film.

DESCRIPTION OF EMBODIMENTS

Preferred embodiments of a wiring substrate and method of manufacturing the wiring substrate disclosed in the present invention will be explained in detail below with reference to the accompanying drawings. Furthermore, the present invention is not limited to the embodiments.

FIG.1is a partial sectional view illustrating configuration of a core substrate100included in a multi-layer wiring substrate according to one embodiment. As illustrated inFIG.1, the core substrate100is a wiring substrate having a base material110, wiring layers120aand120b, wiring layers130aand130b, a magnetic material140, and an insulating resin150. Furthermore, in the following, a description will be made by assuming that the side of one of the surfaces of the base material110on which the wiring layers120aand120bare formed is an upper side and is referred to as an upper surface110a, whereas the side of the other of the surfaces of the base material110on which the wiring layers130aand130bare formed is a lower side and is referred to as a lower surface110b. However, the core substrate100may be used by, for example, vertically inverting the surfaces.

The base material110is a base material of the core substrate100and is configured to include a plate-shaped member having insulation properties. The base material110used may be, for example, a glass epoxy substrate or the like obtained by impregnating a glass cloth with an insulation-property resin, such as an epoxy-based resin or a polyimide-based resin. Furthermore, the base material110used may also be a substrate obtained by impregnating a woven fabric or a non-woven fabric made from glass fibers, a carbon fibers, aramid fibers, or the like with an epoxy-based resin. The thickness of the base material110may be about, for example, 400 to 1200 μm.

The wiring layers120aand120bare formed on the upper surface110aof the base material110, whereas the wiring layers130aand130fcare formed on the lower surface110bof the base material110. Furthermore, a metal foil111included in the wiring layer120bis a metal foil that is previously provided on the upper surface110aof the base material110and that can be removed by performing etching. Similarly, a metal foil112included in the wiring layer130bis a metal foil that is previously provided on the lower surface110bof the base material110and that can be removed by performing etching. Examples of the metal foils111and112used here include a copper foil, a copper alloy foil, or the like. The thickness of each of the metal foils111and112is, for example, 4 to 7 μm.

In the base material110, through-holes113and114passing through the base material110in the thickness direction are drilled. The through-hole113is a through-hole formed in a cylindrical shape having an opening portion with a diameter of about, for example, 300 to 400 μm, and accommodates therein the magnetic material140. Furthermore, the through-hole114is a through-hole formed in a cylindrical shape having an opening portion with a diameter of about, for example, 100 to 200 μm, and accommodated therein the insulating resin150.

The wiring layer120ahas a plurality of electroless plating films and electrolytic plating films, and forms a pad on the upper surface of the magnetic material140. Specifically, the wiring layer120aincludes a first electroless plating film121a, a first electrolytic plating film121b, a second electroless plating film122a, a second electrolytic plating film122b, a third electroless plating film123a, and a third electrolytic plating film123b.

In contrast, the wiring layer120bincludes a plurality of electroless plating films and electrolytic plating films, and forms a pad on the upper surface110aof the base material110. Specifically, the wiring layer120bincludes the metal foil111, the first electroless plating film121a, the first electrolytic plating film121b, the second electroless plating film122a, the second electrolytic plating film122b, the third electroless plating film123a, and the third electrolytic plating film123b.

Namely, the wiring layer120bhas a configuration in which the metal foil111that is previously provided on the upper surface110aof the base material110is added onto the lowermost layer of the wiring layer120a. The electroless plating films121a,122a, and123aconstituting the wiring layers120aand120bare electroless plating films that are simultaneously formed by performing electroless plating. Furthermore, the electrolytic plating films121b,122b, and123bconstituting the wiring layers120aand120bare electrolytic plating films that are simultaneously formed by performing electrolytic plating.

The wiring layer130aincludes a plurality of electroless plating films and electrolytic plating films, and forms a pad on the lower surface of the magnetic material140. Specifically, the wiring layer130aincludes the first electroless plating film121a, the first electrolytic plating film121b, the second electroless plating film122a, the second electrolytic plating film122b, a fourth electroless plating film131a, and a fourth electrolytic plating film131b.

In contrast, the wiring layer130bincludes a plurality of electroless plating films and electrolytic plating films, and forms a pad on the lower surface110bof the base material110. Specifically, the wiring layer130bincludes the metal foil112, the first electroless plating film121a, the first electrolytic plating film121b, the second electroless plating film122a, the second electrolytic plating film122b, the fourth electroless plating film131a, and the fourth electrolytic plating film131b.

Namely, the wiring layer130bhas a configuration in which the metal foil112that is previously provided on the lower surface110bof the base material110is added onto the uppermost layer of the wiring layer130a. The electroless plating films121a,122a, and131aconstituting the wiring layers130aand130bare electroless plating films that are simultaneously formed by performing electroless plating. Furthermore, the electrolytic plating films121b,122b, and131bconstituting the wiring layers130aand130bare electrolytic plating films that are simultaneously formed by performing electrolytic plating.

The magnetic material140is filled in the through-hole113that is formed in the base material110, an upper end portion protrudes from the upper surface110aof the base material110, and a lower end portion protrude from the lower surface110bof the base material110. Specifically, the upper end portion of the magnetic material140protrudes from the upper surface110aof the base material110by an amount substantially similar to the thickness of the metal foil111, and the lower end portion of the magnetic material140protrudes from the lower surface110bof the base material110by an amount substantially similar to the thickness of the metal foil112. The magnetic material140used may be, for example, an insulation-property resin, such as an epoxy-based resin, having magnetic particles. Examples of the magnetic particles includes a filler, such as iron, iron oxide, cobalt iron oxide, ferrosilicon, magnetic alloy, or ferrite.

At the center of the magnetic material140in a plan view, a through-hole141passing through the magnetic material140in the thickness direction of the base material110is drilled. The through-hole141is a through-hole formed in a cylindrical shape having an opening portion with a diameter of about, for example, 100 to 200 μm, and accommodates therein the insulating resin150. On the inner wall surface of the through-hole141, the first electroless plating film121a, the first electrolytic plating film121b, the second electroless plating film122a, and the second electrolytic plating film122bcontinued from the wiring layer120aand the wiring layer130aare laminated in this order. The magnetic material140and the electroless plating films and the electrolytic plating films inside the through-hole141form an inductor. A through-hole122cis formed on the inner side of the second electrolytic plating film122bthat is the innermost layer of the through-hole141, and the insulating resin150is filled into the through-hole122c.

In contrast, on the inner wall surface of the through-hole114formed in the base material110, the second electroless plating film122aand the second electrolytic plating film122bcontinued from the wiring layer120band the wiring layer130bare laminated in this order. Then, the through-hole122cis formed on the inner side of the second electrolytic plating film122bthat is the innermost layer of the through-hole114, and the insulating resin150is filled into the through-hole122c.

In this way, on the inner wall surface of the through-hole141in the magnetic material140, the plating film that is thicker than that of the inner wall surface of the through-hole114by an amount corresponding to the first electroless plating film121aand the first electrolytic plating film121bis formed. Consequently, it is possible to reduce electric resistance in the electroless plating film and the electrolytic plating film inside the through-hole141in the magnetic material140, and it is thus possible to improve the electric characteristics of the inductor embedded in the core substrate100.

In the following, each of the electroless plating films and the electrolytic plating films will be described.

The first electroless plating film121ais formed on the surface of the magnetic material140and the surface of the metal foils111and112. Namely, in the vicinity of the magnetic material140, the first electroless plating film121ais continuously formed so as to in contact with the upper surface of the magnetic material140, the inner wall surface of the through-hole141, and the lower surface of the magnetic material140. In contrast, in the vicinity of the through-hole114, the first electroless plating film121ais laminated on the upper surface of the metal foil111and the lower surface of the metal foil112. The thickness of the first electroless plating film121ais about, for example, 0.4 to 0.6 μm.

The first electrolytic plating film121bis laminated on the first electroless plating film121a. Namely, in the vicinity of the magnetic material140, the first electrolytic plating film121bcontinuously laminated on the first electroless plating film121aon the upper side of the magnetic material140, inside the through-hole141, and on the lower side of the magnetic material140. In contrast, in the vicinity of the through-hole114, the first electrolytic plating film121bis laminated on the upper surface or the lower surface of the first electroless plating film121a. The thickness of the first electrolytic plating film121fcis about for example, 8 to 12 μm on the surface of the core substrate100, and is about, for example, 5 to 7 μm inside the through-hole141. Namely, the electrolytic plating solution is less likely to circulate in the interior of the through-hole141; therefore, the first electrolytic plating film121binside each of the through-hole141is thinner than the surface of the core substrate100.

The first electrolytic plating film121bis laminated on the first electroless plating film121ainside the through-hole141in the magnetic material140. Accordingly, the first electrolytic plating film121bis formed on the surface of the first electroless plating film121ahaving conductivity, so that the first electrolytic plating film121bis able to obtain a uniform thickness inside the through-hole141. Specifically, the magnetic material140is formed of an insulation-property resin, such as an epoxy-based resin, containing magnetic particles; therefore, on the surface of the magnetic material140, the magnetic particles having conductivity and the insulation-property resin without having conductivity are exposed. Then, in a case where electrolytic plating is directly applied to the surface of this type of the magnetic material140, the electrolytic plating film is not deposited at the portion in which the insulation-property resin is exposed. Thus, although an electrolytic plating film is deposited to some extent at the portion in which the magnetic particles are exposed, a portion in which the electrolytic plating film is not formed is generated over the entire surface of the magnetic material140, so that an electrolytic plating film having an insufficient and non-uniform film thickness is formed.

In contrast, as a result of the first electroless plating film121abeing formed on the surface of the magnetic material140, the surface on which the first electrolytic plating film121bis formed has sufficient conductivity, and thus, a sufficient and uniform electrolytic plating film is deposited over the entire surface of the magnetic material140. Because the first electrolytic plating film121bis formed in this way, the surface of the magnetic material140including inside the through-hole141is covered by the satisfactory first electrolytic plating film121b, and electrical continuity inside the through-hole141is ensured. As a result, it is possible to improve the electric characteristics of the inductor that is formed by using the magnetic material140.

The second electroless plating film122ais laminated on the first electrolytic plating film121band is formed not only inside the through-hole141of the magnetic material140but also inside the through-hole114. Namely, in the vicinity of the magnetic material140, the second electroless plating film122ais continuously laminated on the first electrolytic plating film121bon the upper side of the magnetic material140, inside the through-hole141, and on the lower side of the magnetic material140. In contrast, in the vicinity of the through-hole114, the second electroless plating film122ais laminated on the upper surface or the lower surface of the first electrolytic plating film121b, is also formed on the inner wall surface of the through-hole114, and is continuously formed on the upper side of the metal foil111, inside the through-hole114, and on the lower side of metal foil112. The thickness of the second electroless plating film122ais about, for example, 0.4 to 0.6 μm.

The second electrolytic plating film122bis laminated on the second electroless plating film122a. Namely, in the vicinity of the magnetic material140, the second electrolytic plating film122bis continuously laminated on the second electroless plating film122aon the upper side of the magnetic material140, inside the through-hole141, and on the lower side of the magnetic material140. In contrast, in the vicinity of the through-hole114, the second electrolytic plating film122bis continuously laminated on the second electroless plating film122aon the upper side of the metal foil111, inside the through-hole114, and on the lower side of the metal foil112. The thickness of the second electrolytic plating film122bis about, for example, 18 to 22 μm on the surface of the core substrate100, and is about, for example, 16 to 20 μm inside the through-hole141and inside the through-hole114. Namely, the electrolytic plating solution is less likely to circulate in the interior of the through-hole141and the through-hole114; therefore, the second electrolytic plating film122binside each of the through-hole141and the through-hole114is thinner than the surface of the core substrate100.

Furthermore, the second electrolytic plating film122bis thicker than the first electrolytic plating film121b. Consequently, even if an end portion of, for example, a glass cloth contained in the base material110protrudes on the inner wall surface of the through-hole114, the protruding portion is embedded by the second electrolytic plating film122bthat is relatively thick. As a result, it is possible to ensure electrical continuity inside the through-hole114, and also, it is possible to improve the filling property of the insulating resin150with respect to the through-hole122cformed by the second electrolytic plating film122b. Furthermore, the first electrolytic plating film121binside the through-hole141in the magnetic material140is not excessively thickened, so that it is possible to suppress a variation in thickness of the first electrolytic plating film121band improve the electric characteristics of the inductor by ensuring uniform conductivity. Furthermore, inside the through-hole141in the magnetic material140, the second electrolytic plating film122bis laminated on the second electroless plating film122a, the first electroless plating film121a, and the first electrolytic plating film121b, so that the surface of the second electrolytic plating film122bis formed to have sufficient conductivity, and thus, the variation in thickness of the second electrolytic plating film122bis suppressed.

The third electroless plating film123ais laminated on the second electrolytic plating film122bin the wiring layers120aand120b, and is formed on the upper surface of the insulating resin150. Namely, the third electroless plating film123ais laminated, in a planar state, on the upper side of the wiring layers120aand120bthat are formed on the upper surface110aof the base material110. The thickness of the third electroless plating film123ais about, for example, 0.4 to 0.6 μm.

The third electrolytic plating film123bis laminated on the third electroless plating film123a. Namely, the third electrolytic plating film123bis laminated, in a planar state, on the uppermost layer of the wiring layers120aand120fcthat are formed on the upper surface110aof the base material110. The thickness of the third electrolytic plating film123bis about, for example, 13 to 17 μm.

The third electrolytic plating film123bis thicker than the first electrolytic plating film121band is thinner than the second electrolytic plating film122b. Because the third electrolytic plating film123bis thicker than the first electrolytic plating film121b, the upper surface of the insulating resin150is covered by a sufficient strength, and thus, it is possible to prevent protrusion of the insulating resin150caused by a difference in coefficient of thermal expansion with the base material110. As a result, it is possible to ensure electrical connectivity of the upper surface of the wiring layers120aand120b. Furthermore, because the third electrolytic plating film123bis thinner than the second electrolytic plating film122b, the third electrolytic plating film123bis not excessively thick, and thus, miniaturization and densification of the wiring layers120aand120bare not prevented.

The fourth electroless plating film131ais laminated on the second electrolytic plating film122bin the wiring layers130aand130b, and is formed on the lower surface of the insulating resin150. Namely, the fourth electroless plating film131ais laminated, in a planar state, on the lower side of the wiring layers130aand130bthat are formed on the lower surface110bof the base material110. The thickness of the fourth electroless plating film131ais about, for example, 0.4 to 0.6 μm.

The fourth electrolytic plating film131bis laminated on the fourth electroless plating film131a. Namely, the fourth electrolytic plating film131bis laminated, in a planar state, on the lowermost layer of the wiring layers130aand130bthat are formed on the lower surface110bof the base material110. The thickness of the fourth electrolytic plating film131bis about, for example, 13 to 17 μm.

Similarly to the third electrolytic plating film123b, the fourth electrolytic plating film131bis thicker than the first electrolytic plating film121b, and is thinner than the second electrolytic plating film122b. Because the fourth electrolytic plating film131bis thicker than the first electrolytic plating film121bthe lower surface of the insulating resin150is covered by a sufficient strength, and thus, it is possible to prevent protrusion of the insulating resin150caused by a difference in coefficient of thermal expansion with the base material110. As a result, it is possible to ensure electrical connectivity of the lower surface of the wiring layers130aand130b. Furthermore, because the fourth electrolytic plating film131bis thinner than the second electrolytic plating film122b, the fourth electrolytic plating film131bis not excessively thick, and thus, miniaturization and densification of the wiring layers130aand130bare not prevented.

In the following, a manufacturing method of the multi-layer wiring substrate including the core substrate100having configuration described above will be specifically described using examples with reference to the flowchart illustrated inFIG.2.

First, the through-hole113through which the magnetic material140is filled is formed in the base material110that is configured to have a plate-shaped member having insulation properties (Step S101). On the base material110, for example, as illustrated inFIG.3, the metal foil111is formed on the upper surface110athat is the plate-shaped member having insulation properties, and the metal foil112is formed on the lower surface110b. The thickness of the base material110is about, for example, 400 to 1200 μm. On the base material110, for example, as illustrated inFIG.4, the through-hole113having a cylindrical shape with the diameter of the opening portion thereof being about 300 to 400 μm is formed. The through-hole113is formed by performing, for example, laser beam machining or drilling, and, after the through-hole113is formed, a desmear process of removing a resin residue remaining on the inner wall surface is performed. For the desmear process, for example, a potassium permanganate solution may be used.

Then, the magnetic material140is filled in the through-hole113(Step S102). Namely, for example, as illustrated inFIG.5, the magnetic material140that is formed of insulation-property resin containing magnetic particles is filled in the through-hole113that is formed in the base material110. The magnetic material140is filled in the through-hole113without any gap, so that the upper end portion upwardly protrudes from the metal foil111provided on the base material110, and the lower end portion downwardly protrudes from the metal foil112provided on the base material110.

Thus, surface polishing is performed on the protruding portions such that the upper end portion and the lower end portion of the magnetic material140are flush with the surface of the metal foils111and112(Step S103). Namely, for exampleFIG.6, the upper end portion of the magnetic material140is ground such that the upper surface of the metal foil111and the upper surface of the magnetic material140are flush with each other, and the lower end portion of the magnetic material140is ground such that the lower surface of the metal foil112and the lower surface of the magnetic material140are flush with each other.

When the upper surface and the lower surface of the magnetic material140are ground to be plane surfaces, the through-hole141passing through the magnetic material140in the thickness direction of the base material110is formed (Step S104). The through-hole141is formed, for example, as illustrated inFIG.7, at the center of the magnetic material140in a planar view, and has a cylindrical shape with the diameter of the opening portion being about 100 to 200 μm. The through-hole141is formed by performing, for example, laser beam machining or drilling, and, after the through-hole141is formed, the inner wall surface is washed with water in order to remove the residue.

After the through-hole141is formed in the magnetic material140, the first electroless plating film121athat covers a portion exposed on the surface is formed (Step S105). Specifically, for example, as illustrated inFIG.8, for example, electroless copper plating is performed on the upper surface of the metal foil111, the upper surface of the magnetic material140, the inner wall surface of the through-hole141, the lower surface of the magnetic material140, and the lower surface of the metal foil112, so that the first electroless plating film121ais formed. Here, because electroless copper plating is performed, even if the insulation-property resin that does not have conductivity is exposed to the upper surface and the lower surface of the magnetic material140or the inner wall surface of the through-hole141, the first electroless plating film121ais reliably formed. The thickness of the first electroless plating film121ais about, for example, 0.4 to 0.6 μm.

Then, the first electrolytic plating film121bis laminated on the first electroless plating film121a(Step S106). Namely, for example, as illustrated inFIG.9, the first electrolytic plating film121bis formed by performing, for example, electrolytic copper plating on the surface on which the first electroless plating film121ais formed. Here, because electrolytic copper plating is performed on the surface of the first electroless plating film121athat has conductivity, the electrolytic plating film is also sufficiently deposited inside the through-hole141in the magnetic material140, the first electrolytic plating film121bhaving a sufficient film thickness is formed. The thickness of the first electrolytic plating film121bis about, for example, 8 to 12 μm at a portion other than inside the through-hole141, and is about, for example, 5 to 7 μm inside the through-hole141.

When the first electrolytic plating film121bis formed, the through-hole114that passes through the base material110is formed at the position that does not overlap with the magnetic material140(Step S107). Specifically, at the position that does not overlap with the magnetic material140, the through-hole114that passes through, in addition to the base material110, the metal foils111and112provided on the upper and the lower surfaces of the base material110, the first electroless plating film121a, and the first electrolytic plating film121bis formed. Similarly to the through-hole141in the magnetic material140, the through-hole114has a cylindrical shape with the diameter of the opening portion thereof being about 100 to 200 μm. The through-hole114is formed by performing, for example, laser beam machining or drilling, and, after the through-hole114is formed, a desmear process of removing a resin residue remaining on the inner wall surface is performed. For the desmear process, for example, a potassium permanganate solution may be used. An alkaline solution, such as a potassium permanganate solution, used for the desmear process may possibly take away the magnetic particles; however, here, because the magnetic material140is covered by the first electroless plating film121aand the first electrolytic plating film121b, the magnetic particles are not taken away from the magnetic material140.

After the through-hole114is formed, the second electroless plating film122athat covers the portion that is exposed to the surface is formed (Step S108). Specifically, for example, as illustrated inFIG.11, for example, electroless copper plating is performed on the surface on which the first electrolytic plating film121bis formed and is performed on the inner wall surface of the through-hole114, so that the second electroless plating film122ais formed. Here, because electroless copper plating is performed, the second electroless plating film122ais also reliably performed on the inner wall surface of the through-hole114on which the base material110having the insulation properties is exposed. The thickness of the second electroless plating film122ais about, for example, 0.4 to 0.6 μm.

Then, the second electrolytic plating film122bis laminated on the second electroless plating film122a(Step S109). Namely, for example, as illustrated inFIG.12, for example, electrolytic copper plating is performed on the surface on which the second electroless plating film122ais formed, so that the second electrolytic plating film122bis formed. Consequently, on the inner wall surface of the through-hole114, the second electroless plating film122aand the second electrolytic plating film122bare formed. In contrast, on the inner wall surface of the through-hole141in the magnetic material140, in addition to the second electroless plating film122aand the second electrolytic plating film122b, the first electroless plating film121aand the first electrolytic plating film121bare formed. Namely, inside the through-hole141in the magnetic material140, as compared to inside the through-hole114, the plating film having conductivity is thickly formed.

The thickness of the second electrolytic plating film122bis about, for example, 16 to 22 μm at the portion other than the through-hole114and the through-hole141, and is about, for example, 16 to 20 μm inside the through-hole114and the through-hole141. Therefore, a plating film having conductivity with a film thickness of about at least 21 to 27 μm is formed inside the through-hole141in the magnetic material140, and it is thus possible to sufficiently reduce the electric resistance in the subject plating film. As a result, it is possible to improve the electric characteristics of the inductor formed by the magnetic material140and the plating film inside the through-hole141.

As a result of the second electrolytic plating film122bbeing formed, the through-hole122cis formed inside each of the through-hole114and the through-hole141by the second electrolytic plating film122b. Then, the insulating resin150is filled in the through-hole122c(Step S110). Namely, for example, as illustrated inFIG.13, the insulating resin150is filled in the through-hole122cthat is formed inside each of the through-hole114and the through-hole141. The insulating resin150used may be, for example, an epoxy-based resin containing filler, such as silica. The insulating resin150is filled without any gap, so that the upper end portion upwardly protrudes from the opening portion located on the upper side of the through-hole122c, and the lower end portion downwardly protrudes from the opening portion located on the lower side of the through-hole122c.

Thus, surface polishing is performed on the protruding portions such that the upper end portion and the lower end portion of the insulating resin150are flush with the surface of the second electrolytic plating film122b(Step S111). Namely, for example, as illustrated inFIG.14, the upper end portion of the insulating resin150is ground such that the upper surface of the second electrolytic plating film122band the upper surface of the insulating resin150are flush with each other, and the lower end portion of the insulating resin150is ground such that the lower surface of the second electrolytic plating film122band the lower surface of the insulating resin150are flush with each other. Furthermore, the resin residue remaining on the surface of the second electrolytic plating film122bdue to the polishing of the insulating resin150is removed by the desmear process.

Then, the third electroless plating film123aand the fourth electroless plating film131athat cover the portion exposed on the surface is formed (Step S112). Specifically, electroless copper plating is performed on the intermediate structure in which the insulating resin150is ground and the upper surface and the lower surface become plane surfaces, so that, for example, as illustrated inFIG.15, the third electroless plating film123ais formed on the upper surface of the intermediate structure, and the fourth electroless plating film131ais formed on the lower surface of the intermediate structure. Here, because electroless copper plating is performed, the third electroless plating film123aand the fourth electroless plating film131aare also reliably formed on the upper surface and the lower surface of the insulating resin150that do not have conductivity. The thickness of each of the third electroless plating film123aand the fourth electroless plating film131ais about, for example, 0.4 to 0.6 μm.

Then, the third electrolytic plating film123band the fourth electrolytic plating film131bare laminated on the third electroless plating film123aand the fourth electroless plating film131a(Step S113). Namely, because electrolytic copper plating is performed on the intermediate structure in which the third electroless plating film123aand the fourth electroless plating film131aare formed, for example, as illustrated inFIG.16, the third electrolytic plating film123bis laminated on the third electroless plating film123a, and the fourth electrolytic plating film131bis laminated on the fourth electroless plating film131a. The thickness of each of the third electrolytic plating film123band the fourth electrolytic plating film131bis about, for example, 13 to 17 μm.

All of the electroless plating films and the electrolytic plating films are formed as a result of the third electrolytic plating film123band the fourth electrolytic plating film131bbeing formed, and then, etching is performed in order to form the wiring layers120a,120b,130a, and130b(Step S114). Namely, for example, as illustrated inFIG.17, etching resists210are formed at the portions in each of which the plating film is left as wiring and a pad.FIG.17illustrates the etching resists210for forming a pad at the position of each of the through-hole114and the through-hole141in each of which the insulating resin ISO is filled. The diameter of the pad is larger than the diameter of the opening portion of the through-hole114. Furthermore, the diameter of the pad is larger than the diameter of the opening portion of the through-hole141of the magnetic material140and is smaller than the diameter of the opening portion of the through-hole113in which the magnetic material140is filled. Therefore, the etching resist210having the size associated with the diameter of the pad is formed on the surface of each of the third electrolytic plating film123band the fourth electrolytic plating film131b. The etching resists210have desired resolution and are formed of a material that is resistant to etching.

Then, the metal foils111and112, the first electroless plating film121a, the first electrolytic plating film121b, the second electroless plating film122a, the second electrolytic plating film122b, the third electroless plating film123a, the third electrolytic plating film123b, the fourth electroless plating film131a, and the fourth electrolytic plating film131bare removed by being subjected to wet etching by using etching resists210as a masking material. Consequently, for example, as illustrated inFIG.13, the wiring layers120aand120beach having a pad are formed on the upper surface110aof the base material110, and the wiring layers130aand130beach having a pad are formed on the lower surface110bof the base material110. The core substrate100is completed by removing the etching resists210from the wiring layers120a,120b,130a, and130b.

On the upper surface and the lower surface of the core substrate100, the insulating layers and the wiring layers are sequentially build up, and then, the multi-layer wiring substrate is formed (Step S115). Specifically, for example, as illustrated inFIG.19, an insulating layer230and a wiring layer220are laminated on each of the upper surface and the lower surface of the core substrate100, and the wiring layer220that is the uppermost layer is covered by a solder mask layer240. A through-hole is formed in the solder mask layer240, a connecting terminal250that is made of solder or the like and that is used to electrically connect an electronic component, such as a semiconductor chip, to the wiring layer220is formed in this through-hole. In contrast, the wiring layer220that is the lowermost layer is covered by a solder mask layer260. Then, an opening portion is formed on the solder mask layer260, and an external connection pad270formed in the wiring layer220that is the lowermost layer is exposed from the opening portion. The external connection pad270can be electrically connected to external parts or devices. The insulating layers and the wiring layers may be formed by using, for example, a build-up process.

In this way, it is possible to form a multi-layer wiring substrate having the plurality of wiring layers220from the core substrate100having a built-in inductor using the magnetic material140. This multi-layer wiring substrate can be used for a semiconductor device having mounted thereon a part, such as a semiconductor chip. Specifically, as illustrated inFIG.20, a semiconductor chip310is mounted on the upper surface of the multi-layer wiring substrate. For example, the connecting terminal250on the multi-layer wiring substrate and an electrode315, which is made of solder, of the semiconductor chip310are bonded. Then, the bonding portion between the connecting terminal250and the electrode315is sealed by an underfill resin320, and the semiconductor device having mounted thereon the semiconductor chip310is obtained.

As described above, according to the embodiment, a through-hole is formed in the magnetic material that is filled in the base material, and then, after the first electroless plating film and the first electrolytic plating film are formed, another through-hole is formed at a portion other than the magnetic material to form the second electroless plating film and the second electrolytic plating film. Consequently, as compared to the other through-hole, a plating film having a thickness by an amount corresponding to the first electroless plating film and the first electrolytic plating film is formed inside the through-hole in the magnetic material; therefore, it is possible to reduce the electric resistance in the plating film inside the through-hole in the magnetic material, and it is thus possible to improve the electric characteristics of the inductor that is formed by the magnetic material and the plating film inside the through-hole.

According to an aspect of an embodiment of the wiring substrate and the method of manufacturing the wiring substrate disclosed in the present application, an advantage is provided in that it is possible to improve the electric characteristics of a built-in inductor.

With respect to the embodiments and the variety thereof described above, the following note is further disclosed.

(Note) A method of manufacturing a wiring substrate including:

forming a first through-hole in a base material;

filling a magnetic material in the first through-hole;

forming a second through-hole in the magnetic material;

forming a first plating film that covers an inner wall surface of the second through-hole;

forming a third through-hole in the base material; and

forming a second plating film that covers an inner wall surface of the third through-hole and the first plating film, wherein

the forming the first plating film includesforming a first electroless plating film that is in contact with the inner wall surface of the second through-hole, andforming a first electrolytic plating film that is laminated on the first electroless plating film.