Circuit board and electronic module

Abstract

Provided is a circuit board in which, in a configuration in which gaps between wiring patterns are filled with a resin, adhesion of the resin to the surfaces of the wiring patterns is easily prevented or suppressed. A circuit board (10) is provided with: a metal base (12); an insulating layer (14) laminated on the metal base (12); a metal layer (16) which is laminated on the opposite side of the insulating layer (14) from the metal base (12) and constitutes a wiring pattern (18); and a resin part (20) which is made of a thermosetting resin and fills the gap between the wiring patterns (18), and the surface of the resin part (20) is recessed in a curved shape when viewed from the longitudinal direction of the gap.

Description

Technical Field

[0001] The present disclosure relates to a circuit substrate and an electronic module including the circuit substrate. Background Art

[0002] Japanese Patent Publication No. 2021-34534 discloses a circuit substrate in which a circuit portion and a base substrate are stacked with an insulating layer. A wiring pattern is formed on a metal plate constituting the circuit portion by etching, and a resin different from the insulating layer is filled in the gaps between the wiring patterns. Electronic components such as semiconductor elements are mounted on such a circuit substrate, and the electronic components and the circuit substrate are sealed with a sealing resin. Summary of the invention

[0003] Problems to be solved by the invention

[0004] In recent years, with the diversification of the use environment of electronic equipment, the increase of the current capacity of the circuit substrate is required. The current capacity of the circuit substrate can be increased by thickening the metal plate constituting the wiring pattern. However, when the metal plate constituting the wiring pattern is thickened, in the resin sealing process, the sealing resin cannot be fully filled between the wiring patterns, and sometimes residual peeling and bubbles will remain in the insulating layer including the sealing resin and the wiring pattern side. When a voltage is applied to the circuit substrate in this state, partial discharge will be generated from the end of the wiring pattern not covered by the sealing resin to the insulating layer. Such partial discharge becomes the cause of dielectric breakdown.

[0005] In this regard, in the above-mentioned prior art, since the gaps between the wiring patterns are filled with resin, the peeling of the sealing resin and the generation of bubbles as described above can be prevented. However, since the resin filled in the gaps between the wiring patterns adheres to the surface of the wiring patterns, a resin grinding process is required to remove the resin on the surface of the wiring patterns. In the resin grinding process, problems such as clogging of the polisher used for grinding may occur.

[0006] The present disclosure has been made in consideration of the above-mentioned facts, and an object of the present disclosure is to provide a circuit board and an electronic module that can easily prevent or suppress the resin from adhering to the surfaces of wiring patterns in a structure in which gaps between wiring patterns are filled with resin.

[0007] Solutions for solving problems

[0008] The circuit substrate of the first scheme comprises: a base substrate; an insulating layer stacked on the base substrate; a conductor layer stacked on the side of the insulating layer opposite to the base substrate to form a wiring pattern; and a resin portion composed of a thermosetting resin, which fills the gaps between the wiring patterns, and the surface of the resin portion is curved and concave when viewed from the long dimension direction of the gap.

[0009] In the circuit substrate of the first scheme, an insulating layer is stacked on a base substrate, and a conductor layer constituting a wiring pattern is stacked on the side of the insulating layer opposite to the base substrate. The gaps between the wiring patterns are filled with a resin portion composed of a thermosetting resin. The surface of the resin portion is curved and concave when observed from the long dimension direction of the gap between the wiring patterns. As a result, the step between the surface of the wiring pattern and the surface of the resin portion can be reduced. As a result, for example, in the resin sealing process after mounting components on the wiring pattern, it is easy to fill the sealing resin in the above-mentioned step portion, and it is easy to prevent the sealing resin from peeling off and the generation of bubbles. Moreover, as described above, in the structure in which the resin portion with a curved surface concave is arranged in the gap between the wiring patterns, since the surface of the resin portion is lower than the surface of the wiring pattern, it is easy to prevent or inhibit the resin from adhering to the surface of the wiring pattern.

[0010] A circuit board according to a second aspect is the circuit board according to the first aspect, wherein the resin contains a thermally conductive filler.

[0011] According to the circuit board of the second aspect, even if the resin filling the gaps between the wiring patterns adheres to the surface of the wiring patterns, the thermally conductive filler contained in the resin can easily settle in the gaps. As a result, for example, in the polishing step of removing the resin on the surface of the wiring patterns, the number of polishing times can be reduced.

[0012] The circuit board according to a third aspect is the circuit board according to the first aspect or the second aspect, and further comprises a plating layer provided on the surface of the wiring pattern in an unpolished state.

[0013] According to the circuit board of the third aspect, since the plating layer is provided on the surface of the wiring pattern in an unpolished state, oxidation of the surface of the wiring pattern can be prevented.

[0014] An electronic module according to a fourth aspect includes: the circuit substrate according to the first aspect or the second aspect; an electronic component mounted on the circuit substrate; and a sealing resin sealing the circuit substrate and the electronic component.

[0015] In the electronic module of the fourth aspect, the electronic components are mounted on the circuit board, and the circuit board and the electronic components are sealed with a sealing resin. Since the circuit board is the circuit board of the first aspect or the second aspect, the above-mentioned effect is achieved.

[0016] An electronic module according to a fifth aspect includes: the circuit substrate according to the third aspect; an electronic component mounted on the circuit substrate; and a sealing resin sealing the circuit substrate and the electronic component.

[0017] In the electronic module of the fifth aspect, the electronic components are mounted on the circuit board, and the circuit board and the electronic components are sealed with a sealing resin. Since the circuit board is the circuit board of the third aspect, the above-mentioned effect is achieved.

[0018] Effects of the Invention

[0019] As described above, in the circuit board and the electronic module of the present disclosure, in the configuration in which the gaps between the wiring patterns are filled with resin, it is easy to prevent or suppress the resin from adhering to the surfaces of the wiring patterns. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a diagram showing a perspective view of a circuit board according to the embodiment.

[0021] Figure 2 It means along Figure 1 Cross-sectional view of the cut surface along the F2-F2 line.

[0022] Figure 3 It is a flowchart showing the manufacturing process of the circuit board of the embodiment.

[0023] Figure 4 A part of an electronic module of an embodiment Figure 2 The corresponding cross-sectional view.

[0024] Figure 5 It is a flowchart showing the manufacturing process of the circuit board of a comparative example. DETAILED DESCRIPTION

[0025] Below, refer to Figure 1 to Figure 5 A circuit board 10 and an electronic module 30 according to an embodiment of the present disclosure will be described. Figure 1 In FIG. 1 , a circuit board 10 of this embodiment is shown in a three-dimensional diagram. An electronic component (such as a semiconductor element) serving as a heat generating element is mounted on the circuit board 10. Figure 1 and Figure 2 As shown, the circuit board 10 includes: a metal base 12; an insulating layer 14 stacked on the metal base 12; a metal layer 16 stacked on the side of the insulating layer 14 opposite to the metal base 12 and constituting a wiring pattern (circuit pattern) 18; and a resin portion 20 filling the gaps between the wiring patterns 18. The metal base 12 corresponds to the "base substrate" in the present disclosure, and the metal layer 16 corresponds to the "conductor layer" in the present disclosure.

[0026] The metal base 12 is a substrate made of a metal material. As the material of the metal plate constituting the metal base 12, for example, copper, copper alloy, aluminum, aluminum alloy, etc. having high thermal conductivity can be used. The thickness of the metal base 12 is set in the range of 1.0 mm to 3.0 mm, for example. It should be noted that a heat dissipation unit (not shown) such as a heat sink or a radiator may be mounted on the surface of the metal base 12 on the side opposite to the insulating layer 14.

[0027] The insulating layer 14 is formed, for example, by mixing a filler having insulating and thermal conductivity into a synthetic resin having electrical insulating properties. As the above-mentioned synthetic resin, for example, a synthetic resin having high electrical insulating properties and thermal conductivity, such as epoxy resin, which is a thermosetting synthetic resin having an epoxy group, can be used. As the above-mentioned filler, for example, a filler that is chemically stable and has high thermal conductivity and electrical insulating properties, such as silica, alumina, aluminum nitride, and boron nitride can be used. The thickness of the insulating layer 14 is set, for example, in the range of 0.06 mm to 0.2 mm. It should be noted that the insulating layer 14 can also be formed by mixing glass fibers into the synthetic resin having electrical insulating properties instead of the filler having thermal conductivity.

[0028] The metal layer 16 is, for example, made of a conductive metal material. As the metal material constituting the metal layer 16, for example, a rolled copper plate, an aluminum plate, etc. can be used. The thickness of the metal layer 16 is, for example, set in the range of 0.3 mm to 1.5 mm. The metal layer 16 is formed by etching the metal layer on the side opposite to the metal substrate 12 stacked in the insulating layer 14, and constitutes a predetermined wiring pattern 18. The surface of the wiring pattern 18 is not polished, and metal plating is applied to the surface (not shown). It should be noted that the metal layer 16 can also be formed by punching the lead frame material by die stamping. However, in the case of die stamping, burrs are easily generated, so before the metal layer 16 is stacked on the insulating layer 14, a process for removing the burrs is required.

[0029] The resin portion 20 is formed by mixing a filler having insulating and thermal conductivity into a thermosetting resin such as epoxy resin. This filler is equivalent to the "thermal conductive filler" in the present disclosure. As the filler, for example, silica, alumina, etc. can be used. The resin portion 20 is formed by heating a thermosetting resin that fills the gaps between the wiring patterns 18, flowing in the gaps, and then formally solidifying (so-called C-stage). The gaps between the wiring patterns 18 are filled with the resin portion 20. Figure 2 As shown, the surface of the resin portion 20 is curved and concave toward the insulating layer 14 side when viewed from the longitudinal direction of the gap between the wiring patterns 18. This concave is caused by the curing shrinkage of the thermosetting resin.

[0030] Next, a method for manufacturing the circuit board 10 having the above-mentioned structure will be described. Figure 3 , a flowchart is used to show the manufacturing process of the circuit board 10. When manufacturing the circuit board 10, first, a laminated body including the metal base 12, the insulating layer 14, and the metal layer 16 is prepared, and the metal layer 16 is etched to form the wiring pattern 18.

[0031] As a method for manufacturing the above-mentioned laminate, a well-known method can be used. For example, a liquid material (varnish material) can be applied as a material of the insulating layer 14 to at least one of the metal substrate 12 and the metal layer 16 by roller coating, rod coating or screen printing. Afterwards, the liquid material on the metal substrate 12 or on the metal layer 16 is dried by natural drying or forced drying. Thus, the insulating layer 14 is obtained. The insulating layer 14 at this time may also be in an uncured state (the so-called B stage state). Next, a metal layer 16 is formed on the surface of the insulating layer 14. Specifically, a metal layer 16 (for example, a rolled copper plate) is stacked on the surface of the insulating layer 14 to form a wiring pattern 18 by hot pressing or the like. Thus, a laminate in which the metal layer 16 constituting the wiring pattern 18 and the metal substrate 12 are stacked with the insulating layer 14 interposed therebetween is obtained.

[0032] In the next etching step, the metal layer 16 of the laminated body obtained as described above is etched to form a predetermined wiring pattern 18. The laminated body after the etching step is inspected for defects in the next automatic optical inspection step.

[0033] In the next resin filling step, a thermosetting resin mixed with a filler having insulation and thermal conductivity is filled into an area where the wiring spacing between substrate products can be freely designed. Thus, the gaps between the wiring patterns 18 are filled with the thermosetting resin. The filling is performed, for example, by screen printing, dispensing, etc. During the filling, the filling amount of the thermosetting resin is adjusted to prevent or suppress the thermosetting resin from adhering to the surface of the wiring pattern 18.

[0034] In the subsequent formal curing step, the thermosetting resin filled in the gaps between the wiring patterns 18 is heated to be formally cured (C-staged). The heating temperature of the thermosetting resin in the formal curing step is set, for example, in the range of 150°C to 180°C. In the formal curing step, the thermosetting resin whose fluidity is increased by heating is made to flow in the gaps between the wiring patterns 18, and then formally cured. Thus, the resin portion 20 is formed. The surface of the resin portion 20 is curved and concave toward the insulating layer 14 side when viewed from the long dimension direction of the gaps between the wiring patterns 18. That is, in the formal curing step, the thermosetting resin can flow by heating, and the thermosetting resin can flow along the side of the wiring patterns 18, thereby covering the end of the wiring patterns 18 with the thermosetting resin. As a result, the cured thermosetting resin (i.e., the resin portion 20) is in a state where the surface is curved and concave when viewed from the long dimension direction of the gaps between the wiring patterns 18.

[0035] In the next plating step, the surface of the wiring pattern 18 after the formal curing step is not polished but metal plating is applied to the surface (not shown). Thus, the circuit board 10 is completed. The metal plating uses a plating solution of copper, nickel, etc., for example. The thickness of the metal plating is set in the range of 0.1μm to 0.4μm, for example. The metal plating can prevent oxidation of the surface of the wiring pattern 18. The completed circuit board 10 is subjected to final inspection in the next final inspection step.

[0036] Electronic components (not shown) are mounted on the completed circuit board 10. Examples of the electronic components include semiconductor chips, transistors, diodes, light emitting diodes, thyristors, capacitors, resistors, resistor arrays, coils, switches, and the like. The electronic components are bonded to the surface of the wiring pattern 18 using a conductive bonding material such as solder (not shown). The electronic components and the circuit board 10 are sealed with a sealing resin 22 (see FIG. Figure 4 ) is sealed. Thus, the electronic module 30 including the circuit board 10, the electronic components and the sealing resin 22 is completed. The sealing resin 22 is formed by transfer molding, for example.

[0037] Next, the operation and effects of this embodiment will be described.

[0038] In the circuit substrate 10 of the above-mentioned structure, an insulating layer 14 is stacked on a metal base 12, and a metal layer 16 constituting a wiring pattern 18 is stacked on the side of the insulating layer 14 opposite to the metal base 12. The gaps between the wiring patterns 18 are filled with a resin portion 20 composed of a thermosetting resin. The surface of the resin portion 20 is curved and concave when viewed from the long dimension direction of the gap between the wiring patterns 18. As a result, the step between the surface of the wiring pattern 18 and the surface of the resin portion 20 can be reduced. As a result, in the resin sealing process after mounting components on the wiring pattern 18, it is easy to fill the sealing resin 22 in the above-mentioned step portion, and it is easy to prevent the sealing resin 22 from peeling off and the generation of bubbles. Moreover, as described above, in the structure in which the resin portion 20 with a curved surface concave is provided in the gap between the wiring patterns 18, since the surface of the resin portion 20 is lower than the surface of the wiring pattern 18, it is easy to prevent or suppress the resin from adhering to the surface of the wiring pattern 18.

[0039] Reference Figure 5 The above effects are supplemented. Figure 5 , a flowchart is used to show the manufacturing process of the circuit board of the comparative example. In this comparative example, a pre-curing process and a resin polishing process are provided between the resin filling process and the main curing process, but other than that, the process is the same as the present embodiment.

[0040] In this comparative example, in the resin filling process, in order to fully fill the gaps between the wiring patterns with thermosetting resin, the surface of the wiring pattern is also attached with thermosetting resin. In the subsequent pre-curing process, the thermosetting resin present in the surface of the wiring pattern and the gaps between the wiring patterns is heated and pre-cured (B-staged). In the subsequent resin grinding process, the surface of the wiring pattern is ground using, for example, a ceramic polisher to remove the resin on the surface of the wiring pattern. However, since the ceramic polisher may be clogged, productivity may deteriorate.

[0041] In contrast, in this embodiment, since it is easy to prevent or suppress the resin from adhering to the surface of the wiring pattern 18, the above-mentioned pre-curing step and the resin polishing step can be omitted, and the number of polishing times in the resin polishing step can be reduced. As a result, the productivity of the circuit board 10 is greatly improved.

[0042] Furthermore, according to the circuit board 10 of this embodiment, even if the thermosetting resin filling the gaps between the wiring patterns 18 adheres to the surface of the wiring patterns 18, the thermally conductive filler contained in the thermosetting resin easily settles in the gaps, thereby reducing the number of times of polishing in the resin polishing step.

[0043] Although the present disclosure has been described above by showing the embodiment, the present disclosure can be implemented with various modifications within the scope not departing from the gist thereof. In addition, the scope of rights of the present disclosure is of course not limited to the above-described embodiment.

[0044] In addition, the entire disclosure of Japanese Patent Application No. 2022-175151 filed on October 31, 2022 is also incorporated into this specification by reference. All documents, patent applications, and technical standards described in this specification are incorporated into this specification by reference to the same extent as if each document, patent application, and technical standard was specifically and individually described as being incorporated into this specification by reference.

Claims

1. A circuit substrate comprising: base substrate; an insulating layer, laminated on the base substrate; A conductor layer, stacked on the side of the insulating layer opposite to the base substrate, forming a wiring pattern; as well as The resin portion is made of a thermosetting resin and fills the gaps between the wiring patterns. The surface of the resin portion is concave in a curved shape when viewed from the longitudinal direction of the gaps.

2. The circuit substrate according to claim 1, wherein: The resin contains a thermally conductive filler.

3. The circuit board according to claim 1 or 2, comprising: The plating layer is provided on the surface of the wiring pattern in an unpolished state.

4. An electronic module comprising: The circuit substrate according to claim 1 or 2; an electronic component mounted on the circuit substrate; and The sealing resin seals the circuit substrate and the electronic component.

5. An electronic module comprising: The circuit substrate according to claim 3; an electronic component mounted on the circuit substrate; and The sealing resin seals the circuit substrate and the electronic component.

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