Assembled board

The assembled board includes: an insulating board including a plurality of product regions disposed in a central portion and a marginal region disposed in an outer peripheral portion; a conductor layer disposed on an upper surface side and a lower surface side of the insulating board, the conductor layer having a volume different between the upper surface side and the lower surface side; and a solder resist layer laminated on the upper and lower surfaces of the insulating board, and a plurality of openings are formed in the solder resist layer on a surface on a side with a smaller volume of the conductor layer so that a volume in the marginal region of the solder resist layer becomes smaller than a volume in the marginal region of the solder resist layer on a surface on an opposite side.

BACKGROUND OF THE INVENTION

1. Technical Field

The present disclosure relates to an assembled board with a high-density wiring conductor.

A plan view and a main part enlarged cross-sectional view of the conventional assembled board B are shown inFIGS. 2A and 2B. Such an assembled board B is described, for example, in Japanese Unexamined Patent Application Publication No. 2013-172073. The assembled board B includes an insulating board10, a conductor layer12, and a solder resist layer13. In a top view, the insulating board10includes a plurality of product regions X to be the individual wiring boards, and a marginal region Y surrounding the product regions X. Although twelve product regions X are illustrated in the assembled board B, the assembled board B actually includes several tens to several hundreds of product regions X.

In the insulating board10, the insulating layers for the build-up10bare laminated on the upper and lower surfaces of the insulating layer for the core10a. A plurality of through holes14are formed in the insulating layer for the core10acorresponding to the product region X. A through-hole conductor12aincluding a part of the conductor layer12is filled inside the through hole14. A plurality of via holes15are formed in the insulating layers for the build-up10bcorresponding to the product region X. A via conductor12bincluding a part of the conductor layer12is filled inside the via hole15.

The conductor layer12is formed on the surface of and inside the insulating board10. The conductor layer12is formed, for example, by using a well-known plating method. Part of the conductor layer12formed on the upper surface of the insulating board10functions as the semiconductor-element connection pad16. The electrode of the semiconductor element is connected to the semiconductor-element connection pad16through the solder. Part of the conductor layer12formed on the lower surface of the insulating board10functions as the external connection pad17. The wiring conductor of the external electric circuit board is connected to the external connection pad17through the solder.

This causes the semiconductor element and the external electric circuit board to connect each other electrically, and causes the semiconductor element to be activated by transmission and reception of electrical signals through the conductor layer12. The insulating board10where the conductor layer12is formed has a coefficient of thermal expansion of about 10 to 20 ppm/° C.

The solder resist layer13is formed on the upper and lower surfaces of the insulating board10. The solder resist layer13formed on the upper surface includes the opening13aexposing the central portion of the semiconductor element connection pad16. The solder resist layer13formed on the lower surface includes the opening13bexposing the central portion of the external connection pad17. The resin paste or film, for example, formed of electrically insulating materials is applied or adhered onto the surface of the insulating layer for the build-up10bto be thermally cured, whereby the solder resist layer13is formed. The solder resist layer13has a thickness of about 15 to 20 μm. The solder resist layer13has a coefficient of thermal expansion of about 60 ppm/° C.

By the way, as described above, when the solder resist layer13is heated to be cured, a stress due to the contraction of the solder resist layer13occurs on the upper surface side and the lower surface side of the insulating board10due to the difference in coefficients of thermal expansion between the insulating board10and the solder resist layer13. In such a state, for example, when the volume of the conductor layer12on the upper surface side of the wiring board10is smaller than the volume of the conductor layer12on the lower surface side of the wiring board10, the stiffness on the upper surface side of a smaller volume of the conductor layer12becomes small as compared to the stiffness on the lower surface side. Therefore, the assembled board B sometimes warps to the upper surface side due to the contraction stress of the solder resist layer13.

In particular, in the corner portion of the assembled board B in a position away from the central portion of the assembled board B, the stress is large, and there is a tendency for the upward warpage to increase. For this reason, when a semiconductor element is mounted on the assembled board B, the height of the semiconductor-element connection pad becomes uneven. As a result, there is a problem that the electrode of the semiconductor element and the semiconductor-element connection pad cannot be fully joined through the solder, and that the semiconductor element cannot be stably operated.

SUMMARY

The assembled board of the present disclosure includes: an insulating board including a plurality of product regions disposed in a central portion and a marginal region surrounding the central portion, the marginal region disposed in an outer peripheral portion; a conductor layer disposed on an upper surface side and a lower surface side of the insulating board corresponding to the product regions and the marginal region, the conductor layer having a volume different between the upper surface side and the lower surface side; and a solder resist layer laminated from the central portion to the outer peripheral portion of the upper and lower surfaces of the insulating board, and a plurality of openings are formed in the solder resist layer on a surface on a side with a smaller volume of the conductor layer so that a volume in the marginal region of the solder resist layer becomes smaller than a volume in the marginal region of the solder resist layer on a surface on an opposite side.

DETAILED DESCRIPTION

In the assembled board of the present disclosure, a plurality of openings are formed in the solder resist layer on a surface on a side with a smaller volume of the conductor layer so that a volume in the marginal region of the solder resist layer becomes smaller than a volume in the marginal region of the solder resist layer on a surface on an opposite side. For this reason, the stress at the time of contraction of the solder resist layer can be reduced on the side of a smaller volume of the conductor layer and smaller stiffness. Thus, the warpage of the assembled board is reduced so that the electrode of the semiconductor element and the semiconductor-element connection pad are reliably joined, whereby the assembled board allowing the semiconductor element to operate stably can be provided.

The assembled board according to one embodiment of the present disclosure will be described with reference toFIGS. 1A and 1B. The assembled board A shown inFIG. 1Aincludes an insulating board1, a conductor layer2, and a solder resist layer3. In a top view, the insulating board1includes a plurality of product regions X to be the individual wiring boards, and a marginal region Y surrounding the product regions X.

As shown inFIG. 1B, the insulating board1includes a structure where the insulating layers for the build-up1bare laminated on the upper and lower surfaces of the insulating layer for the core1a. The insulating layers1aand1bare formed of electrically insulating material where the glass cloth is impregnated with an insulating resin such as an epoxy resin or a bismaleimide triazine resin so as to be cured.

As shown inFIG. 1B, the insulating layer for the core1aincludes a plurality of through holes4in the product region X. A through-hole conductor2aincluding a part of the conductor layer2is formed inside the through hole4. The through hole4is formed, for example, by drill processing or blast processing, and has a diameter of about 50 to 300 μm.

As shown inFIG. 1B, the insulating layer for the build-up1bincludes a plurality of via holes5in the product region X. A via conductor2bincluding a part of the conductor layer2is formed inside the via hole5. The via hole5is formed, for example, by laser processing, and has a diameter of about 30 to 100 μm.

The conductor layer2is formed of a highly conductive metal such as copper on the surface of and inside the insulating board1, for example, by the well-known semi-additive method or subtractive method. The conductor layer2has a thickness of about 15 to 20 μm. In the assembled board A according to the one embodiment, the volume of the conductor layer2disposed on the upper surface side of the insulating board1is smaller than the volume of the conductor layer2disposed on the lower surface side of the insulating board1.

Part of the conductor layer2formed on the upper surface of the insulating board1functions as the semiconductor-element connection pad6. The electrode of the semiconductor element is connected to the semiconductor-element connection pad6through the solder. Part of the conductor layer2formed on the lower surface of the insulating board1functions as the external connection pad7. The wiring conductor of the external electric circuit board is connected to the external connection pad7through the solder. This causes the semiconductor element and the external electric circuit board to connect each other electrically, and causes the semiconductor element to be activated by transmission and reception of electrical signals through the conductor layer2.

The solder resist layer3is formed by deposition or application followed by thermal curing of an electrically insulating sheet or a paste containing a thermosetting resin such as an epoxy resin or a polyimide resin on the upper and lower surfaces of the insulating board1. The solder resist layer3formed on the upper surface includes the opening3aexposing the central portion of the semiconductor-element connection pad6. The solder resist layer3formed on the lower surface includes the opening3bexposing the central portion of the external connection pad7.

The solder resist layer3formed on the surface on the side of a smaller volume of the conductor layer2, that is, the upper surface of the insulating board1has a plurality of openings3cso that the volume in the marginal region Y is smaller than the volume in the marginal region Y of the solder resist layer3on the opposite side. The length of one side of the opening3cis usually greater than 0.1 mm from the limit of manufacture. As shown inFIG. 1A, the opening3cis disposed in the corner portion of the marginal region Y.

According to the assembled board A according to the one embodiment of the present disclosure, a plurality of openings3care formed in the solder resist layer3on the surface on the side of a smaller volume of the conductor layer2so that the volume in the marginal region Y of the solder resist layer3becomes smaller than the volume in the marginal region of the solder resist layer3on the surface on the opposite side. For this reason, the stress at the time of contraction of the solder resist layer3can be reduced on the side of a smaller volume of the conductor layer2and smaller stiffness. In particular, when the opening3cis disposed in the corner portion of the marginal region Y, the stress can be reduced more effectively. Thus, the warpage of the assembled board A is reduced so that the electrode of the semiconductor element and the semiconductor-element connection pad6are reliably joined, whereby the assembled board allowing the semiconductor element to operate stably can be provided.

The present disclosure is not limited to the above embodiments, and various modifications are possible without departing from the scope of the present disclosure. For example, in the assembled board A according to the one embodiment described above, as shown inFIGS. 1A and 1B, the openings3chave an equal-sized quadrangular shape. However, each of the openings3cmay have a different size. Furthermore, the opening3cmay have other shapes such as polygonal shapes such as a triangular shape, a pentagonal shape, and a hexagonal shape, circular shapes, and oval shapes, and various shapes may be mixed.

In the assembled board A according to the one embodiment described above, as shown inFIGS. 1A and 1B, the opening3cis disposed in the corner portion of the marginal region Y. However, if disposed in the marginal region, the opening does not necessarily need to be disposed in the corner portion of the marginal region.

In the assembled board A according to the one embodiment described above, as shown inFIGS. 1A and 1B, the insulating board1has a quadrangular shape. However, the insulating board may have another shape such as a polygonal shape such as a triangular shape, a pentagonal shape, and a hexagonal shape, a circular shape, and an oval shape.

Furthermore, in the assembled board A according to the one embodiment described above, as shown inFIGS. 1A and 1B, a plurality of product regions X are arranged lengthwise and breadthwise. However, the product region may not necessarily be arranged lengthwise and breadthwise, and the product region may be arranged depending on the shape of, for example, the insulating board.