Aluminum wiring heat dissipation substrate

Abstract

An aluminum wiring heat dissipation substrate (1) comprises: a resin layer (2) that comprises an insulating resin material; aluminum wiring (3) that serves as a wiring pattern and comprises aluminum disposed on one surface of the resin layer (2); a solder connection part (4) that is made of metal (excluding aluminum), is formed on the aluminum wiring (3), and is to be connected to an electronic component by soldering; and a heat dissipation layer (5) that is made of metal and is disposed on the other surface of the resin layer (2).

Description

Aluminum wiring heat dissipation board

[0001] The present invention relates to an aluminum wiring heat dissipation board in which aluminum is used as a wiring pattern.

[0002] Semiconductor elements in electrical circuits tend to generate more heat due to higher density and current. This higher current also requires measures such as thicker wiring patterns. The substrates on which such heat-generating components are mounted are formed as heat-dissipating substrates, incorporating heat-dissipating members to form a heat dissipation path that dissipates heat generated by the heat-generating components toward the opposite side of the substrate. Specifically, the heat generated by the heat-generating components is cooled by conducting it to a heat sink or the like on the back side of the substrate (the side opposite the component mounting surface (mounting surface)) (see, for example, Patent Document 1).

[0003] International Publication No. 2021 / 024445

[0004] However, as shown in Patent Document 1, copper is generally used for wiring patterns from the viewpoint of electrical resistivity and thermal conductivity. In recent years, in order to meet the demand for large currents and heat dissipation, the thickness of the wiring patterns needs to be increased, but this increases the weight, which is a problem.

[0005] On the other hand, aluminum is known to be lighter than copper, but aluminum is passive and naturally forms a strong oxide film, making it unsolderable. For this reason, aluminum wiring, which uses aluminum as a wiring pattern, is not used on boards where components are mounted using solder.

[0006] The present invention has been made in consideration of the above-mentioned conventional technology, and aims to provide an aluminum wiring heat dissipation board that allows components to be mounted by solder even when aluminum wiring is used, can handle large currents, and is lightweight.

[0007] In order to achieve the above object, the present invention provides an aluminum wiring heat dissipation board comprising: a resin layer made of an insulating resin material; aluminum wiring as a wiring pattern arranged on one side of the resin layer; a solder connection part made of metal (excluding aluminum) formed on the aluminum wiring and to be connected to an electronic component by soldering; and a metal heat dissipation layer arranged on the other side of the resin layer.

[0008] Preferably, the solder connection portion is directly joined to the aluminum wiring.

[0009] Preferably, the aluminum wiring is formed within the width of the solder connection portion in a cross-sectional view, and further has a narrow portion formed narrower than the width of the solder connection portion.

[0010] Preferably, the heat dissipation layer is formed of a first layer made of copper disposed on the resin layer side, and a second layer made of aluminum directly bonded to the first layer.

[0011] Preferably, a thin film layer made of zinc is interposed between the aluminum wiring and the solder connection portion.

[0012] According to the present invention, since the wiring pattern is aluminum wiring made of aluminum, even if the wiring pattern becomes thick for use in a high-current board that requires high density and high current, it is possible to prevent the weight from becoming too large. Since solder connections are formed on the aluminum wiring, electronic components can be mounted by soldering even if aluminum is used for the wiring pattern.

[0013] Furthermore, since the solder connection portion and the aluminum wiring are directly joined, there is no need to provide any connecting layer to arrange the metal solder connection portion on the aluminum wiring, which simplifies the structure.

[0014] Furthermore, since the aluminum wiring does not have any wider sections than the solder joints in cross section, the distance between adjacent aluminum wirings can be narrowed while still ensuring the width of the solder joints for soldering, which allows for a high density wiring pattern, which is a significant advantage when used as a high current board.

[0015] Furthermore, by forming the heat dissipation layer from the first and second layers, the heat transferred can first be dissipated horizontally through the first copper layer, and then the heat transferred to the second layer can be dissipated vertically through the second aluminum layer. This allows the entire heat dissipation layer to be used to dissipate heat, resulting in efficient heat dissipation.

[0016] Furthermore, by interposing a thin film layer of zinc between the aluminum wiring and the solder joint, it is possible to provide a solder joint even for aluminum wiring that cannot be connected to metal by plating, making it possible to form a wiring pattern using aluminum on which electronic components can be mounted by soldering.

[0017] Fig. 1 is a schematic cross-sectional view of an aluminum wiring heat dissipation board according to the present invention. Fig. 2 is a flowchart showing a method for manufacturing an aluminum wiring heat dissipation board. Fig. 3 is an explanatory diagram of a lamination step. Fig. 4 is an explanatory diagram of an etching resist formation step. Fig. 5 is an explanatory diagram of a first etching step. Fig. 6 is an explanatory diagram of a second etching step. Fig. 7 is a schematic cross-sectional view of another aluminum wiring heat dissipation board according to the present invention.

[0018] As shown in FIG. 1 , the aluminum wiring heat dissipation board 1 according to the present invention includes a resin layer 2 made of an insulating resin material. This resin layer 2 can be made of an organic material, such as epoxy resin, filled with an inorganic filler with high thermal conductivity, such as alumina or boron nitride. Its thermal conductivity is between 1 and 30 (W / m·K). Aluminum wiring 3, which serves as a wiring pattern made of aluminum, is disposed on one side (the upper side in FIG. 1 ). Solder connection portions 4 are formed on the aluminum wiring 3 for connection to electronic components (not shown) by soldering. Because aluminum is passive and naturally forms a strong oxide film, making it unsolderable, these solder connection portions 4 are made of a metal other than aluminum. A heat dissipation layer 5 made of a metal, i.e., a metallic material, is disposed on the other side (the lower side in FIG. 1 ) of the resin layer 2. Heat generated by the electronic components travels from the solder connection 4 to the aluminum wiring 3 and then through the resin layer 2, and is released to the outside by the heat dissipation layer 5. The thickness of the solder connection 4 is preferably 3% to 50% of the total thickness of the aluminum wiring 3 and the solder connection 4. This is because thicker aluminum wiring 4 made of aluminum contributes to weight reduction.

[0019] This structure prevents excessive weight increase even when the wiring pattern is thickened for use in high-current boards requiring high density and high current. Furthermore, because solder connections 4 are formed on the aluminum wiring 3, electronic components can be mounted by soldering even when the wiring pattern is made of aluminum. Conventionally, copper was primarily used for both the wiring pattern and the solder connections for soldering, but increasing the thickness of the wiring pattern inevitably resulted in increased weight. In the present invention, by using aluminum wiring 3 for the wiring pattern and providing solder connections 4 at the locations where soldering is required, weight increase is not a significant issue even when the wiring pattern is thickened. This is because aluminum is lighter, with a specific gravity approximately one-third that of copper. Compared to copper, aluminum has inferior electrical resistivity, thermal conductivity, and ease of etching, making it difficult to use aluminum for wiring patterns for mounting such electronic components by soldering from the perspectives of management and production. The present invention makes use of aluminum, which has been avoided as a wiring pattern, in order to realize its lightweight characteristics for use in high-current boards. By using aluminum for the wiring pattern, weight and costs can be reduced compared to when the wiring pattern and solder joints are all made of copper, and soldering is possible in the same way as with copper. Furthermore, because the heat dissipation layer 5 and aluminum wiring 3 are both made of aluminum, warping does not occur when electronic components are mounted (reflow mounting), as occurs when these materials are dissimilar.

[0020] As is clear from FIG. 1 , the solder connection 4 is directly bonded to the aluminum wiring 3. Direct bonding means that there is nothing interposed between the solder connection 4 and the aluminum wiring 3, and the solder connection 4, which is made of a metal material, and the aluminum wiring 3, which is made of aluminum, are directly bonded by metal bonding. For example, if the solder connection 4 is made of copper, the copper and aluminum can be bonded by pressing them together with pressure, by exploding the copper and aluminum together and bonding them through the impact, or by pouring molten aluminum onto the copper to bond them. That is, a so-called copper-aluminum clad material can be used to form the solder connection 4 with the aluminum wiring 3. In such a copper-aluminum clad material, the solder connection 4 and the aluminum wiring 3 are directly bonded, eliminating the need for any connecting layer to place the metal solder connection 4 on the aluminum wiring 3, simplifying the structure.

[0021] As shown in FIG. 1 , the aluminum wiring 3 is formed within the width of the solder connection 4 in a cross-sectional view. Furthermore, the aluminum wiring 3 has a narrow width portion 6 that is narrower than the width of the solder connection 4. Therefore, the outer edge of the aluminum wiring 3 does not extend beyond the outer edge of the solder connection 4 in a cross-sectional view. In other words, since the aluminum wiring 3 does not have a portion that is wider than the solder connection 4 in a cross-sectional view, the distance between adjacent aluminum wirings 3 can be narrowed while ensuring the width of the solder connection 4 for soldering. This allows for a high-density wiring pattern. This is highly effective for use as a high-current board. The presence of the narrow width portion 6 also allows for further weight reduction.

[0022] Here, the heat dissipation layer 5 may be formed simply from a metal as a single material. However, it is preferable that the heat dissipation layer 5 be formed from a first layer 5a made of copper disposed on the resin layer 2 side and a second layer 5b made of aluminum directly bonded to the first layer 5a. By forming the heat dissipation layer 5 from the first layer 5a and the second layer 5b in this manner, the heat transferred thereto can first be dissipated horizontally through the first layer 5a made of copper, and then the heat transferred to the second layer 5b can be dissipated vertically (downward in Figure 1 ) through the second layer 5b made of aluminum. Because the copper in the first layer 5a has high thermal conductivity, heat from the electronic components first spreads horizontally and then, over time, is transferred to the aluminum in the second layer 5b, allowing it to be dissipated vertically. This allows the entire heat dissipation layer 5 to be used for efficient heat dissipation. A copper-aluminum clad material can be used for the heat dissipation layer 5.

[0023] The aluminum wiring heat dissipation board 1 having the above structure can be manufactured as follows.

[0024] As shown in FIG. 2 , the lamination process begins with step S1. This process involves laminating a circuit conductor material 7, made of a copper-aluminum clad material, a resin layer 2, and a heat dissipation layer 5 under heat and pressure. As shown in FIG. 3 , the circuit conductor material 7 is formed of aluminum and copper, which will eventually become the aluminum wiring 3 and solder connection 4. Next, the etching resist process (step S2) is performed. As shown in FIG. 4 , this process involves attaching a dry film 8 to the circuit conductor material 7, exposing it to light, and developing it to form an etching resist. Next, the first etching process (step S3) is performed. As shown in FIG. 5 , this process involves etching only copper using a selective etching solution that dissolves only copper but not aluminum. Because copper and aluminum have different etchabilities (solubility), etching them together would make it difficult to ensure a stable circuit shape. Therefore, the second etching process (described below) is used to selectively etch copper and aluminum. Therefore, in the first etching process, a mixed solution of sulfuric acid and hydrogen peroxide (sulfated water) is used to etch only the copper on the surface of the circuit conductor material 7. As a result, the surface layer of the circuit conductor material 7 becomes the solder connection portion 4 .

[0025] Next, the second etching step (step S4) is performed. As shown in FIG. 6, this step involves etching only the aluminum using a selective etching solution that is less likely to dissolve copper and etches only the aluminum. As a result, the aluminum portion of the circuit conductor material 7 becomes the aluminum wiring 3. A ferric chloride aqueous solution can be used as the selective etching solution. The dry film 8 is then peeled off to obtain the aluminum wiring heat dissipation board 1 shown in FIG. 1. Alternatively, in the second etching step, an alkaline solution (e.g., a sodium hydroxide aqueous solution) can be used as the selective etching solution to peel off the dry film 8 and further etch the aluminum. Since aluminum is an amphoteric metal, using an alkaline solution allows it to be dissolved together with the dry film. In either case, the copper solder connection 4 formed in the first etching step functions as an etching resist. When aluminum is selectively etched in the second etching step, the upper side of the aluminum is etched narrower than the lower side, forming a narrow portion 6. Since the copper that forms the solder connection 4 functions as a resist, the aluminum is etched from directly below the copper, and the lower side surface of the aluminum (the lower outer edge of the aluminum) is contained within the outer edge of the solder connection 4.

[0026] As shown in FIG. 7 , another aluminum wiring heat dissipation board 1 according to the present invention may have a thin film layer 9 made of zinc interposed between the aluminum wiring 3 and the solder connection 4. Aluminum is a difficult-to-plate material, and copper, tin, gold, and other metals used for the solder connection 4 cannot be directly plated with aluminum. However, by zincating the aluminum surface (forming a thin film of zinc on the aluminum surface), copper, tin, gold, and other metals can be plated through the thin film layer 9 made of zinc. By interposing the thin film layer 9 made of zinc between the aluminum wiring 3 and the solder connection 4, the solder connection 4 can be formed even on aluminum wiring 3 that cannot be connected to metals by plating. This allows the formation of a wiring pattern using aluminum to which electronic components can be mounted by soldering.

[0027] 1: aluminum wiring heat dissipation substrate, 2: resin layer, 3: aluminum wiring, 4: solder connection portion, 5: heat dissipation layer, 5a: first layer, 5b: second layer, 6: narrow width portion, 7: circuit conductor material, 8: dry film, 9: thin film layer

Claims

1. An aluminum wiring heat dissipation board comprising: a resin layer made of an insulating resin material; aluminum wiring as a wiring pattern arranged on one side of the resin layer; a metal (excluding aluminum) solder connection part formed on the aluminum wiring to be connected to an electronic component by soldering; and a metal heat dissipation layer arranged on the other side of the resin layer.

2. The aluminum wiring heat dissipation board according to claim 1, wherein the solder connection portion is directly joined to the aluminum wiring.

3. The aluminum wiring heat dissipation board according to claim 2, characterized in that the aluminum wiring is formed within the width of the solder connection portion in a cross-sectional view and further has a narrow portion formed narrower than the width of the solder connection portion.

4. An aluminum wiring heat dissipation board according to any one of claims 1 to 3, characterized in that the heat dissipation layer is formed of a first layer made of copper arranged on the resin layer side and a second layer made of aluminum directly bonded to the first layer.

5. The aluminum wiring heat dissipation board according to claim 1, wherein a thin film layer made of zinc is interposed between the aluminum wiring and the solder connection portion.

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