Wiring substrate and method for manufacturing the same

The present application is based upon and claims the benefit of priority to Japanese Patent Application No. 2022-188921, filed Nov. 28, 2022, the entire contents of which are incorporated herein by reference.

The present invention relates to a wiring substrate and a method for manufacturing the wiring substrate.

Description of Background Art

Japanese Patent Application Laid-Open Publication No. 2022-30289 describes a wiring substrate that includes an insulating layer formed from inorganic particles and a resin, a seed layer formed on the insulating layer, and a conductor layer formed on the seed layer. The entire contents of this publication are incorporated herein by reference.

According to one aspect of the present invention, a wiring substrate includes an insulating layer including inorganic particles and resin, a seed layer formed on a surface of the insulating layer, and a conductor layer including a conductor pattern and formed on the seed layer. The surface of the insulating layer is a roughened surface formed such that the roughened surface of the insulating layer has exposed portions of the inorganic particles and resin with gaps at interfaces where the inorganic particles and the resin are in contact, and the seed layer is formed on the roughened surface of the insulating layer such that the seed layer is formed along the exposed portions of the inorganic particles and resin exposed on the roughened surface of the insulating layer and is not formed in the gaps at the interfaces where the inorganic particles and the resin are in contact.

According to another aspect of the present invention, a method for manufacturing a wiring substrate includes forming an insulating layer including inorganic particles and resin, roughening a surface of the insulating layer such that the surface of the insulating layer has a roughened surface and that the roughened surface has exposed portions of the inorganic particles and resin with gaps at interfaces where the inorganic particles and the resin are in contact, forming a seed layer on the roughened surface of the insulating layer such that the seed layer is formed along the exposed portions of the inorganic particles and resin exposed on the roughened surface of the insulating layer and is not formed in the gaps at the interfaces where the inorganic particles and the resin are in contact, and forming a conductor layer on the seed layer such that the conductor layer has a conductor pattern.

A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:

FIG. 1 is a cross-sectional view schematically illustrating a wiring substrate according to an embodiment of the present invention;

FIGS. 2 A- 2 D are each a cross-sectional view schematically illustrating processes of a method for manufacturing a wiring substrate according to an embodiment of the present invention; and

FIG. 3 is a cross-sectional view schematically illustrating an example of a conventional wiring substrate.

Embodiments will now be described with reference to the accompanying drawings, wherein like reference numerals designate corresponding or identical elements throughout the various drawings.

Wiring Substrate

A wiring substrate according to an embodiment of the present invention is described below with reference to the drawings.

FIG. 1 is a cross-sectional view schematically illustrating a wiring substrate according to an embodiment of the present invention. In FIG. 1 , a wiring substrate 1 includes an insulating layer 4 containing multiple inorganic particles 2 and a resin 3 , a seed layer 5 formed on a surface ( 4 a ) of the insulating layer 4 , and a conductor layer 6 of a predetermined conductor pattern formed on the seed layer 5 . It is also possible to form a build-up substrate by stacking multiple wiring substrates 1 each having the above-described structure.

In a wiring substrate 1 according to an embodiment of the present invention, the inorganic particles 2 and the resin 3 are exposed on the surface ( 4 a ) of the insulating layer 4 with gaps 7 at the interfaces where the inorganic particles 2 and the resin 3 are in contact, a surface of the resin 3 (a portion of the surface ( 4 a )) is roughened to become a rough surface, the seed layer 5 is not formed in the gaps 7 between the inorganic particles 2 and the resin 3 , and it is formed along the inorganic particles 2 and the resin 3 exposed on the surface ( 4 a ) of the insulating layer 4 . The roughened surface of the resin 3 preferably has a surface roughness of 0.05 micron or more and 0.2 micron or less Further, the seed layer 5 is preferably a sputtering film. Further, it is preferable that the seed layer 5 is a sputtering film and includes a first layer, which is formed of a copper alloy, and a second layer, which is formed on the first layer and is formed of copper.

According to the wiring substrate 1 described above, the seed layer 5 is not formed in the gaps 7 between the inorganic particles 2 and the resin 3 and is formed along the inorganic particles 2 and the resin 3 exposed on the surface ( 4 a ) of the insulating layer 4 . Therefore, it is possible to prevent a short circuit between conductor patterns caused by the seed layer 5 remaining between the inorganic particles 2 and the resin 3 without being completely removed by etching during a formation process of the conductor patterns. Further, since the inorganic particles 3 exposed on the surface ( 4 a ) of the insulating layer 4 have an anchor effect, adhesion strength between the insulating layer 4 and the seed layer 5 is maintained.

Method for Manufacturing Wiring Substrate

In a method for manufacturing a wiring substrate according to an embodiment of the present invention, the surface ( 4 a ) of the insulating layer 4 are roughened, and by sputtering on the roughened surface ( 4 a ) of the insulating layer 4 , the seed layer 5 is formed along the inorganic particles 2 and the resin 3 exposed on the surface ( 4 a ) of the insulating layer 4 without being formed in the gaps 7 between the inorganic particles 2 and the resin 3 . In the following, with reference to FIGS. 2 A- 2 D , processes of a method for manufacturing a wiring substrate according to an embodiment of the present invention are described.

First, as illustrated in FIG. 2 A , the insulating layer 4 containing the multiple inorganic particles 2 and the resin 3 is formed. In the formation of the insulating layer 4 , for example, a film-like resin 3 containing multiple inorganic particles 2 in a resin such as an epoxy resin is used. By using such a film-like resin 3 , the insulating layer 4 containing the multiple inorganic particles 2 and the resin 3 is formed.

Next, as illustrated in FIG. 2 B , the surface ( 4 a ) of the insulating layer 4 is roughened, and the inorganic particles 2 and the resin 3 are exposed on the surface ( 4 a ) of the insulating layer 4 with gaps 7 at the interfaces where the inorganic particles 2 and the resin 3 are in contact. The surface ( 4 a ) of insulating layer 4 is treated, for example, with a potassium permanganate solution treatment. In this case, the roughening is preferably performed such that a surface roughness of a rough surface of the resin 3 , which forms a part of the surface ( 4 a ), is 0.05 microns or more and 0.2 microns or less.

Next, as illustrated in FIG. 2 C , by sputtering on the roughened surface ( 4 a ) of the insulating layer 4 , the seed layer 5 is formed along the inorganic particles 2 and the resin 3 exposed on the surface ( 4 a ) of insulating layer 4 without being formed in the gaps 7 between the inorganic particles 2 and the resin 3 . Here, the seed layer 5 is formed by sputtering. As a result, compared to a conventional case of forming the seed layer 5 by electroless plating, even when there are some gaps 7 at interfaces where the inorganic particles 2 and resin 3 exposed on the surface ( 4 a ) of the insulating layer 4 contact each other, the seed layer 5 is formed along the inorganic particles 2 and the resin 3 exposed on the surface ( 4 a ) of the insulating layer 4 .

Next, as illustrated in FIG. 2 D , on the seed layer 5 formed by sputtering, the conductor layer 6 is formed. The conductor layer 6 is formed, for example, by electrolytic plating using copper. Further, the conductor layer 6 is patterned using a resist and quick etching.

According to the method for manufacturing the wiring substrate described above, after the surface ( 4 a ) of the insulating layer 4 is roughened, the seed layer 5 is formed by sputtering. Particles forming the seed layer 5 collide perpendicularly with the surface ( 4 a ) of insulating layer 4 . Therefore, adhesion strength between the surface ( 4 a ) and the seed layer 5 is high. Further, it is formed along the inorganic particles 2 and the resin 3 exposed on the surface ( 4 a ) of the insulating layer 4 .

Japanese Patent Application Laid-Open Publication No. 2022-30289 describes a wiring substrate that includes an insulating layer formed from inorganic particles and a resin, a seed layer formed on the insulating layer, and a conductor layer formed on the seed layer. Some of the inorganic particles are separated from the resin, and a part of the seed layer is formed between the inorganic particles and the resin.

According to a technology described in Japanese Patent Application Laid-Open Publication No. 2022-30289, adhesion strength between an insulating layer and a conductor layer may increase via a seed layer. On the other hand, as illustrated in FIG. 3 , a part of a seed layer 54 is formed between inorganic particles 52 and a resin 53 exposed on a surface ( 51 a ) of an insulating layer 51 . That is, the seed layer 54 remains between the inorganic particles 52 and the resin 53 and is not completely removed by etching during a formation process of conductor patterns. Therefore, a short circuit may occur between the conductor patterns.

A wiring substrate according to an embodiment of the present invention includes an insulating layer that contains multiple inorganic particles and a resin, a seed layer that is formed on a surface of the insulating layer, and a conductor layer that has a predetermined conductor pattern and is formed on the seed layer. The inorganic particles and the resin are exposed on the surface of the insulating layer with gaps at the interfaces where the inorganic particles and the resin are in contact. A surface of the resin is a roughened surface. The seed layer is formed along the inorganic particles and the resin exposed on the surface of the insulating layer without being formed in the gaps between the inorganic particles and the resin.

A method for manufacturing a wiring substrate according to an embodiment of the present invention includes forming an insulating layer that contains multiple inorganic particles and a resin; roughening a surface of the insulating layer such that the inorganic particles and the resin are exposed on the surface of the insulating layer with gaps at the interfaces where the inorganic particles and the resin are in contact and that the surface of the insulating layer has a rough surface, forming a seed layer along the inorganic particles and the resin exposed on the surface of the insulating layer without forming the seed layer in the gaps between the inorganic particles and the resin, by sputtering on the roughened surface of the insulating layer, and forming a conductor layer on the seed layer.

Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.