Method for manufacturing circuit board

Abstract

In a configuration in which gaps between wiring patterns are filled with a resin, a resin polishing step for removing the resin on the surfaces of the wiring patterns is omitted. A method for manufacturing a circuit board includes: a preparation step of preparing a laminate in which a conductive layer constituting a wiring pattern and a base substrate are laminated with an insulating layer interposed therebetween; a resin filling step of filling a gap between the wiring patterns with a thermosetting resin; and a main curing step of heating the thermosetting resin so that the thermosetting resin flows in the gaps between the wiring patterns and then main curing the thermosetting resin.

Description

Technical Field

[0001] The present disclosure relates to a method for manufacturing a circuit board. Background Art

[0002] In Japanese Patent Laid-Open No. 2021-34534, a circuit board in which a circuit portion and a base substrate are laminated with an insulating layer therebetween is disclosed. On a metal plate constituting the circuit portion, a wiring pattern is formed by etching, and a resin different from the insulating layer is filled in a gap between the wiring patterns. Electronic components such as semiconductor elements are mounted on such a circuit board, and the electronic components and the circuit board 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 usage environment of electronic devices, an increase in the current capacity of circuit boards has been required. The current capacity of a circuit board can be increased by thickening a metal plate constituting a wiring pattern. However, when the metal plate constituting the wiring pattern is thickened, in the resin sealing process, the sealing resin cannot be sufficiently filled between the wiring patterns, and peeling and bubbles may sometimes remain in the insulating layer including the sealing resin and the side surfaces of the wiring patterns. When a voltage is applied to the circuit board in such a state, partial discharge occurs from the end of the wiring pattern not covered by the sealing resin to the insulating layer. Such partial discharge becomes a cause of insulation breakdown.

[0005] In this regard, in the above-mentioned prior art, since a resin is filled in the gap between the wiring patterns, generation of peeling and bubbles of the sealing resin as described above can be prevented. However, since the resin filled in the gap between the wiring patterns adheres to the surface of the wiring pattern, a resin grinding process for removing the resin on the surface of the wiring pattern is required. In the resin grinding process, problems such as clogging of a polishing pad for grinding occur.

[0006] In view of the above facts, an object of the present disclosure is to obtain a method for manufacturing a circuit board that can omit a resin grinding process for removing the resin on the surface of a wiring pattern in a configuration in which a resin is filled in a gap between wiring patterns.

[0007] Means for Solving the Problems

[0008] A method for manufacturing a circuit board according to a first aspect includes: a preparation step of preparing a laminate in which a conductor layer constituting a wiring pattern and a base substrate are laminated with an insulating layer therebetween; a resin filling step of filling a thermosetting resin in a gap between the wiring patterns; and a formal curing step of heating the thermosetting resin to flow it in the gap and then formally curing it.

[0009] In the method for manufacturing a circuit board according to the first aspect, in the preparation step, a laminate in which a conductor layer constituting a wiring pattern and a base substrate are laminated with an insulating layer therebetween is prepared. In the resin filling step, for example, by filling a thermosetting resin in a region where the wiring interval between the substrate products can be freely designed, the thermosetting resin is filled in the gaps between the wiring patterns. In the formal curing step, the thermosetting resin between the wiring patterns is heated, and after the thermosetting resin flows between the narrow wiring patterns in the substrate body, it is formally cured. Through this flow, the thermosetting resin can be well spread over the gaps between the wiring patterns. As a result, in the resin filling step, it is not necessary to increase the filling amount of the thermosetting resin to the extent that the thermosetting resin adheres to the surface of the wiring pattern. Thus, the resin grinding step for removing the thermosetting resin on the surface of the wiring pattern can be omitted.

[0010] The method for manufacturing a circuit board according to the second aspect is that in the first aspect, after the formal curing step, there is a plating step of plating the surface of the wiring pattern without grinding the surface of the wiring pattern.

[0011] According to the method for manufacturing a circuit board according to the second aspect, in the plating step after the formal curing step, the surface of the wiring pattern is plated without grinding the surface of the wiring pattern. Through this plating, oxidation of the surface of the wiring pattern can be prevented.

[0012] The method for manufacturing a circuit board according to the third aspect is that in the first aspect or the second aspect, in the formal curing step, the thermosetting resin is cured into a state in which the surface of the thermosetting resin is curved and recessed when viewed from the long dimension direction of the gap.

[0013] According to the method for manufacturing a circuit board according to the third aspect, in the formal curing step, the thermosetting resin is cured into a state in which the surface of the thermosetting resin is curved and recessed when viewed from the long dimension direction of the gap between the wiring patterns, forming a resin portion. Thus, 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 step 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 peeling of the sealing resin and the generation of bubbles.

[0014] Advantages of the Invention

[0015] As described above, in the method for manufacturing a circuit board of the present disclosure, in the configuration in which a resin is filled in the gap between the wiring patterns, the resin grinding step for removing the resin on the surface of the wiring pattern can be omitted. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a view showing the configuration of a perspective view of a circuit board manufactured by the method for manufacturing a circuit board according to the embodiment.

[0017] Figure 2 It represents a cross-sectional view of the cross-section along the F2 - F2 line of Figure 1 .

[0018] Figure 3 It is a flowchart showing the manufacturing process of the method for manufacturing a circuit board according to an embodiment.

[0019] Figure 4 It represents a cross-sectional view corresponding to a part of an electronic module constituted by including the circuit board according to the embodiment and Figure 2 .

[0020] Figure 5 It is a flowchart showing the manufacturing process of the method for manufacturing a circuit board according to a comparative example. Detailed Embodiment

[0021] Hereinafter, with reference to Figures 1 to 5 , a method for manufacturing a circuit board according to an embodiment of the present disclosure will be described. In Figure 1 , a circuit board 10 manufactured by the method for manufacturing a circuit board according to this embodiment is shown in a three-dimensional view. An electronic component (for example, a semiconductor element) serving as a heat generating body is mounted on the circuit board 10. As shown in Figure 1 and Figure 2 , the circuit board 10 includes: a metal substrate 12; an insulating layer 14 laminated on the metal substrate 12; a metal layer 16 laminated on the side of the insulating layer 14 opposite to the metal substrate 12 and constituting a wiring pattern (circuit pattern) 18; and a resin portion 20 filled in the gaps between the wiring patterns 18. The metal substrate 12 corresponds to the "substrate board" in the present disclosure, and the metal layer 16 corresponds to the "conductor layer" in the present disclosure.

[0022] The metal substrate 12 is a substrate made of a metal material. As the material of the metal plate constituting the metal substrate 12, for example, materials with high thermal conductivity such as copper, copper alloy, aluminum, and aluminum alloy can be used. The thickness of the metal substrate 12 is set, for example, in the range of 1 mm to 3 mm. It should be noted that on the surface of the metal substrate 12 on the side opposite to the insulating layer 14, heat dissipation units (not shown) such as heat sinks and radiators may be assembled.

[0023] The insulating layer 14 is formed, for example, by mixing a filler having insulating and heat-conductive properties into a synthetic resin having electrical insulation properties. As the above synthetic resin, for example, an epoxy resin, which is a thermosetting synthetic resin having an epoxy group, and other synthetic resins having high electrical insulation and heat conductivity can be used. As the above filler, for example, materials such as silica and alumina, which are chemically stable and have high heat conductivity and electrical insulation, can be used. The thickness of the insulating layer 14 is set, for example, within 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 a synthetic resin having electrical insulation properties instead of a heat-conductive filler.

[0024] The metal layer 16 is formed of a conductive metal material, for example. 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 1 is set, for example, within the range of 0.3 mm to 1.5 mm. The metal layer 16 is formed by etching a metal layer on the side opposite to the metal substrate 12 in the insulating layer 14 to form a prescribed wiring pattern 18. The surface of the wiring pattern 18 is not polished, and metal plating (not shown) is performed on this surface. It should be noted that the metal layer 16 can also be formed, for example, by punching a lead frame material with a die. However, in the case of die punching, since burrs and the like are likely to be generated, a process for removing the above burrs is required before laminating the metal layer 16 on the insulating layer 14.

[0025] The resin portion 20 is formed, for example, by mixing a filler having insulating and heat-conductive properties into a thermosetting resin such as an epoxy resin. As this filler, for example, silica, alumina, etc. can be used. The resin portion 20 is formed by heating a thermosetting resin filled in the gaps between the wiring patterns 18 so that it flows in the above gaps and then is officially cured (so-called C-stage). The gaps between the wiring patterns 18 are filled by the resin portion 20. As Figure 2 shown, when the surface of the resin portion 20 is observed from the long dimension direction of the gaps between the wiring patterns 18, it is recessed in a curved surface shape toward the insulating layer 14 side. This recess is caused by the curing shrinkage of the thermosetting resin.

[0026] Next, a method for manufacturing a circuit board for manufacturing the above-described circuit board 10 will be described. In Figure 3 a flowchart shows the manufacturing process of the method for manufacturing a circuit board according to the present embodiment. In the method for manufacturing a circuit board according to the present embodiment, first, a laminate in which the metal substrate 12, the insulating layer 14, and the metal layer 16 are laminated is prepared, and the wiring pattern 18 is formed by etching the metal layer 16.

[0027] As a method for manufacturing the above laminate, a known method can be used. For example, a liquid material (varnish material) can be applied as a material for the insulating layer 14 to at least one of the metal substrate 12 and the metal layer 16 by a roll coating method, a bar coating method, or a screen printing method. Thereafter, the liquid material on the metal substrate 12 or 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 incompletely cured state (a 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) that becomes the wiring pattern 18 is laminated on the surface of the insulating layer 14 by hot pressing or the like. Thus, a laminate is obtained in which the metal layer 16 constituting the wiring pattern 18 and the metal substrate 12 are laminated with the insulating layer 14 therebetween.

[0028] In the subsequent etching process, the metal layer 16 of the laminate obtained as described above is etched to form a predetermined wiring pattern 18. The laminate after the etching process is inspected for defects in the subsequent automatic optical inspection process. The above etching process and automatic optical inspection process correspond to the "preparation process" in the present disclosure.

[0029] In the subsequent resin filling process, a thermosetting resin mixed with a filler having insulating properties and heat conductivity is filled into an area where the wiring interval between the substrate products can be freely designed. Thus, the thermosetting resin is filled into the gaps between the wiring patterns 18. This filling is performed, for example, by screen printing. At the time of this filling, the filling amount of the thermosetting resin is adjusted to prevent or suppress the adhesion of the thermosetting resin to the surface of the wiring pattern 18.

[0030] In the subsequent formal curing process, the thermosetting resin filled into the gaps between the wiring patterns 18 is heated to be formally cured (C-staged). The heating temperature of the thermosetting resin in this formal curing process is, for example, set in the range of 150°C to 180°C. In this formal curing process, the thermosetting resin whose fluidity has been increased by heating is caused to flow in the gaps between the wiring patterns 18, and then it is formally cured. Thus, the resin portion 20 is formed. The surface of the resin portion 20 is recessed in a curved shape toward the insulating layer 14 when viewed from the long dimension direction of the gaps between the wiring patterns 18. That is to say, in the formal curing process, the thermosetting resin can be caused to flow by heating, and the thermosetting resin can be caused to flow along the side surfaces of the wiring pattern 18, whereby the ends of the wiring pattern 18 can be covered with the thermosetting resin. As a result, the cured thermosetting resin (i.e., the resin portion 20) is in a state where its surface is recessed in a curved shape when viewed from the long dimension direction of the gaps between the wiring patterns 18.

[0031] In the subsequent plating process, metal plating (not shown) is performed on the surface of the wiring pattern 18 after the formal curing process without grinding the surface. Thus, the circuit board 10 is completed. For example, plating solutions such as copper and nickel are used for this metal plating. The thickness of this metal plating is set, for example, within the range of 0.1 μm to 0.4 μm. By this metal plating, oxidation of the surface of the wiring pattern 18 can be prevented. The completed circuit board 10 undergoes a final inspection in the subsequent final inspection process.

[0032] Electronic components (not shown) are mounted on the completed circuit board 10. As such electronic components, for example, semiconductor chips, transistors, diodes, light-emitting diodes, thyristors, capacitors, resistors, resistor arrays, coils, switches, etc. can be cited. These electronic components are joined to the surface of the wiring pattern 18 using a conductive joining material such as solder (not shown). The electronic components and the circuit board 10 are sealed with a sealing resin 22 (refer to Figure 4 ). Thus, an electronic module 30 including the circuit board 10, the electronic components, and the sealing resin 22 is completed. The above-mentioned sealing resin 22 is formed, for example, by transfer molding.

[0033] Next, the functions and effects of the present embodiment will be described.

[0034] According to the present embodiment, in the preparation process, a laminate in which the metal layer 16 and the metal substrate 12 constituting the wiring pattern 18 are laminated with an insulating layer 14 therebetween is prepared. In the resin filling process, a thermosetting resin is filled in the gaps between the wiring patterns 18. In the formal curing process, the thermosetting resin between the wiring patterns 18 is heated and flows in the gaps between the wiring patterns 18 and then undergoes formal curing. By this flow, the thermosetting resin can be well spread over the gaps between the wiring patterns 18. As a result, in the resin filling process, it is not necessary to increase the filling amount of the thermosetting resin to the extent that the thermosetting resin adheres to the surface of the wiring pattern 18. Thus, the grinding process for removing the resin on the surface of the wiring pattern 18 can be omitted.

[0035] Refer to Figure 5 to supplement the description of the above effects. In this Figure 5 , the manufacturing process of the circuit board of the comparative example is shown in a flowchart. In this comparative example, a pre-curing process and a resin grinding process are provided between the resin filling process and the formal curing process, but other than that, it is the same as the present embodiment.

[0036] In this comparative example, in the resin filling process, in order to sufficiently fill the thermosetting resin in the gaps between the wiring patterns, the thermosetting resin also adheres to the surfaces of the wiring patterns. In the subsequent pre-curing process, the thermosetting resin present on the surfaces of the wiring patterns and in the gaps between the wiring patterns is heated and pre-cured (B-staged). In the subsequent resin grinding process, for example, a ceramic polisher is used to grind the surfaces of the wiring patterns to remove the resin on the surfaces of the wiring patterns. However, since the ceramic polisher becomes clogged, the productivity deteriorates. In contrast, in the present embodiment, since the above pre-curing process and resin grinding process are not required, the productivity is significantly improved.

[0037] Furthermore, according to the present embodiment, in the formal curing process, the thermosetting resin cures into a state in which the surface of the thermosetting resin is curved and recessed when viewed in the long dimension direction of the gaps between the wiring patterns 18, forming the resin portion 20. Thereby, the step between the surface of the wiring pattern 18 and the surface of the resin portion 20 can be reduced. As a result, for example, 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 step portion, and it is easy to prevent the peeling of the sealing resin 22 and the generation of bubbles.

[0038] Furthermore, according to the present embodiment, even when the thermosetting resin filled in the gaps between the wiring patterns 18 adheres to the surfaces of the wiring patterns 18, the filler contained in the thermosetting resin easily settles into the above gaps. Thereby, even when a resin grinding process is performed, the number of grinding times can be reduced.

[0039] As described above, the embodiments have been described for the present disclosure, but the present disclosure can be variously modified without departing from its gist. In addition, the scope of rights of the present disclosure is of course not limited to the above embodiments.

[0040] In addition, the entire disclosure of Japanese Patent Application No. 2022-175150 filed on October 31, 2022 is also incorporated herein by reference. Regarding all the documents, patent applications, and technical standards described in this specification, they are incorporated herein by reference to the same extent as if each document, patent application, and technical standard were specifically and individually described as being incorporated herein by reference.

Claims

1. A method for manufacturing a circuit board, comprising: a preparation step of preparing a laminate in which a conductor layer constituting a wiring pattern and a base substrate are laminated with an insulating layer interposed therebetween; a resin filling step of filling a thermosetting resin into a gap between the wiring patterns; and a formal curing step of heating the thermosetting resin to cause it to flow in the gap and then causing it to be formally cured.

2. The method for manufacturing a circuit board according to claim 1, wherein, after the formal curing step, there is a plating step of plating the surface of the wiring pattern without grinding the surface.

3. The method for manufacturing a circuit board according to claim 1 or 2, wherein, in the formal curing step, the thermosetting resin is cured into a state in which the surface of the thermosetting resin is curved and recessed when viewed from the long dimension direction of the gap.

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