JPS62176188A - Manufacture of large current capacity circuit board which facilitates wire bonding - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] (Field of Application in Mll) The present invention relates to a manufacturing method for forming a circuit on a foil-covered substrate made of dissimilar metals. The present invention relates to a method for manufacturing a large current power module substrate that can be used for high current and wire bonding.

(Prior art) Conventionally, in order to manufacture a substrate tS that has both wire bonding and large Kfl functions, circuits were formed using thick steel foil of 70 μm (2 oz.) or 105 μm (3 oz.). The circuit is then plated with precious metal or N
It was necessary to plate the x4 with a base metal, or to bond a wire-bondable metal piece such as an A1 piece to the thick copper 76.

However, the disadvantages are that etching thick copper foil takes time, that plating is expensive and difficult to achieve uniform plating, and that it takes a lot of man-hours to join metal pieces. .

On the other hand, as a more sophisticated method, a method is used in which a substrate made of a composite metal foil of aluminum and copper is bonded together, and an aluminum bonding pad is formed by etching (Japanese Patent Laid-Open No. 58-48432). Publication), the 0g of this aluminum bonding pad is because a large number of aluminum pads can be formed at the same time at a desired location by etching with good reproducibility, and because ultrasonic bonding with an aluminum wire results in an aluminum-aluminum bond. The scope of work is wide, and the tendency to tilt is high.

(Problems to be Solved by the Invention) In recent years, there has been a strong demand for substrates on which power elements can be multiplied. The output of power module substrates, typically represented by inverters, has been increasing year by year, and in addition to having high heat conductivity and wire bonding properties, it has become important to be able to conduct heat flow. Ta.

However, as mentioned above, the copper foil used in Inugami is thick, so etching takes time, resulting in high costs, and it is difficult to form high-density circuits (Special Publications Publication No. 54-8
510) and that it was difficult to form a wire bonding pad.

Therefore, a method using a board laminated with the aforementioned composite metal foil of aluminum and copper could be considered, but in this type of board for high-density circuits, the copper foil is thin and the current is high. Since it could not be flushed, a manufacturing method was devised that involved partially applying thick copper plating.

That is, to give one example, an aluminum foil 3 is placed on the base 1.
A plating/etching resist 4 is formed by screen printing on the aluminum/@foil-covered V board shown in Fig. 6, which has the upper layer and the copper foil 2 as the lower layer. After selectively etching only 3 (Fig. 8), thick copper plating of 5v7oμm was performed (Fig. 9).
After removing the resist, apply etching resist ink 6 again.
fCil printed (Fig. 0), aluminum etching and copper etching (Fig. 11), and finally resist ink 6 and 1n are removed.

However, the thickness of the resist 4 formed by screen printing in the manufacturing method described above is as thin as 10 to 20 μm, while the thickness of the thick copper plating 5 is as thick as 70 μm. However, when printing the etching resist ink 6 in the next step, the resist cannot form a gap between the aluminum pattern and the copper pattern, and the edge is likely to be broken at that position during etching.

In order to solve this problem, it was necessary to prevent the plated copper from protruding on both sides as shown in FIG. After intensive research on how to solve this problem, it became clear that it is better to make the metal resist as thick as possible, to make the plating as high as possible, and to make the resist wall surface as close to vertical as possible.

As a result, a new manufacturing method using a dry film was completed, in which a thick resist film can be formed at one time, and the walls of the mesh resist are nearly vertical.

(Means for Solving the Problems) That is, the present invention forms an etching resist in a desired portion of a dissimilar metal composite foil-clad insulating substrate, and selectively etches only the upper metal foil of the dissimilar metal composite foil. The process of
After peeling off the etching resist, a dry film is pasted on the selectively etched surface of the insulating substrate to form a desired pattern, and thick copper plating is applied. After peeling off the dry film, the dissimilar metal composite This is a method for manufacturing a large current circuit board capable of wire bonding, which comprises the step of etching the metal foil underlying the foil.

The present invention will be explained in more detail below with reference to the drawings.

FIG. 5 shows an example of a circuit board manufactured by the manufacturing method of the present invention, in which a circuit consisting of an insulating substrate 1 and a copper foil 2 as a lower layer of a dissimilar metal composite 76 and an upper layer of the composite foil are shown. This is a cross section in which a circuit made of aluminum foil 3 and a copper circuit formed by thick steel plating 5 are rusted.

The process of manufacturing the circuit board shown in Figure 5 is as follows: First, using the insulating board covered with different metal foils as shown in Figure 6, the desired pattern is etched onto the aluminum foil 3, which is the upper layer metal of the dissimilar metal composite foil. Form a resist. This resist formation may be performed by a screen printing method (using resist ink) or a photo method (dry film or liquid photoresist).

Next, the aluminum foil 3 is selectively etched using an aluminum selective etching agent. After completely peeling off the etching resist, a plating-resistant dry film 7 with a resist thickness of 60 μm or more is laminated onto the desired location (Fig. 1), and then the area where the thick copper plating 5 is to be applied using the photo method is coated. The dry film 7 is developed and removed (Fig. 2), and the thick copper plating 5
(Figure 6). Next, after peeling off the dry film 7 (FIG. 4), selective copper etching is performed to produce the circuit board shown in FIG. 6.

In addition, in the present invention, as an alternative method, as a next step after the step shown in FIG. 4, an etching resist '1 is formed on the entire pattern by a screen printing method or a photo method, and then the etching resist is peeled off after performing copper etching. The circuit board shown in FIG. 5 can also be manufactured by this method.

According to the method according to the present invention described above, there is no protrusion at both ends when thick copper plating is performed as shown in FIG. 9 as in the case of a conventional circuit board, and furthermore, there is no protrusion at both ends as shown in FIGS. 10 to 11 due to the process. Cut off
Since there is no process that is likely to cause R, highly reliable circuits can be formed.

The insulating base of the dissimilar metal foil-clad insulating substrate used in the present invention includes:
Examples include paper phenol resin, glass epoxy resin, etc., but metal plates made of aluminum, copper, aluminum alloy, copper alloy, alumite, etc. with good thermal conductivity and insulated with resin may also be used. In particular, the resin contains inorganic powder with good thermal conductivity, such as alumina powder, boron nitride powder, beryllia powder,
Epoxy resin containing magnesia powder, quartz powder, etc.
Thermosetting resins such as polyimide resins and phenol resins have good thermal conductivity and are preferable as resins for insulating the metal plate.

The plating-resistant dry film used in the present invention is required to have electrolytic copper plating resistance and metal etching resistance. Also, the thickness of 4 does not depend on the thickness of the copper to be plated, but at least 6
A resist thickness of 0 μm or more is required, and the maximum thickness is 60 μm.
It is 0 μ mouth. If the resist is thicker than this, exposure and development will not be successful, and peeling will take a long time, which is not practical.

Next, the different metal foils to be laminated to the substrate used in the present invention include:
There are foils in which aluminum foil 3 and copper foil 2 are rolled and pressure-bonded, foils in which aluminum foil is plated with copper, foils in which aluminum foil is plated with nickel and copper in sequence, and foils in which aluminum is deposited on copper foil. Here, the aluminum part is necessary to serve as a wire bonding pad when mounting a semiconductor hair chip. Also, alternatives to aluminum include nickel, gold, and silver.

Further, the thick copper plating on the copper foil of the present invention is performed by electrolytic plating. This thick copper plating is for carrying a large current, and the plating thickness including the fabric is 65 μm or more, preferably 4 μm or more.
The diameter is 5 to 300 μm, more preferably 50 to 150 μm. If the plating thickness is less than 65μL, the large current carrying capacity will not be excellent, and is there an upper limit? [There is no tlJ limit, but the limit is about 600 μm due to cost.

The selective etching agent for copper used in the present invention includes, but is not particularly limited to, peroxide-based etching agents such as ammonium persulfate aqueous solution and sulfuric acid/hydrogen peroxide-based etching agents.

On the other hand, as a selective etching agent for aluminum, an inorganic strong alkaline aqueous solution such as a caustic soda aqueous solution or a caustic potassium aqueous solution containing various additives is used.

Next, methods for thick copper plating include sulfuric acid steel plating in an acidic bath and copper pyrophosphate plating in an alkaline bath, but the method is not particularly limited to either method.

Since the plating is thick, it is important to plate it quickly and uniformly.

(Example) Next, the steps of the present invention will be explained using Examples, but the present invention is not limited thereto.

Example 1 As a metal-based highly thermally conductive substrate, a composite metal foil consisting of a 40 μm aluminum foil 3 (upper layer) and a 10 μm copper foil 2 (lower layer 7!1) was used as a filler and an epoxy resin insulating layer 8 (8
A HITT plate (manufactured by Denki Kagaku Kogyo Co., Ltd., trade name) was used, which was laminated on the substrate 1 of an aluminum plate of 6.0 mm with a thickness of 0 μm) interposed therebetween. The back side of the substrate was coated with an adhesive and covered with a protective film 9 made of polyvinyl chloride film.

Next, an alkali-resistant etching resist ink was printed on the aluminum foil 3 by screen printing and dried. Thereafter, selective etching was performed using a caustic etchant to expose the lower copper foil 2.

Next, a solvent-developed dry film 7 (Riston 1220 (-F" made by Yubon Co., Ltd., trade name) with a resist thickness of 50 μm was laminated at 100°C using a hot roll laminator (Fig. 1). Bend over and expose
After degreasing and cleaning the dry film 7-covered board shown in Fig. 2 developed in chlorocene at 20°C, it was plated in a sulfuric acid copper plating tank at 65°C at a current of 4A/d for 80 minutes. What happened to electrolytic copper plating (Figure 6)? The thickness of the copper foil after plating was about 90 μm.

Next, the dry film 7 was peeled off with methylene chloride (Fig. 4) and etched at 52°C using a sulfuric acid/hydrogen peroxide based etching solution.
A pattern having a sharp cross section as shown in FIG. 5 was obtained by etching. The total copper foil thickness of the obtained pattern was approximately 80 μm.

Example 2 Using the same substrate as in Example 1, the circuit board shown in FIG. 4 was obtained through the same steps. Next, etching resist ink was formed on the entire pattern by screen printing. After drying, the copper foil portion was etched using a sulfuric acid/hydrogen peroxide based etching solution, and then the etching resist was removed using chlorocene to obtain the circuit board shown in FIG. The total thickness of the obtained copper foil was about 90 μm.

Comparative Example Using the same substrate as in Example 1, screen printing was performed six times to form an etching and plating resist similar to that shown in FIG. The thickness of the resist was 30 μm. Next, selective etching of aluminum was carried out in the same manner as in Example 1, and the same plating treatment as in Example 1 was carried out. vf after thick plating
The r-plane had a shape with protrusions at both ends as in the ninth factor.

Next, an etching resist was formed by screen printing in the same way as in Figure 10, but the resist could not be printed well between the protrusions at both ends of the thick plated part and the aluminum foil, so the next aluminum etching and copper etching were carried out on the circuit. Some of the necessary copper and aluminum foil was also etched away, causing the circuit to break.

(Effects of the Invention) As explained above, the wire-bondable high-current circuit board produced by the manufacturing method of the present invention has thick plated parts that occur when thick plating is performed using a matte resistor formed by screen printing. Since there is no wire breakage and sharp patterns can be formed, the defect rate is low and the reliability is high.

[Brief explanation of drawings]

1 to 4 are cross-sectional views of the circuit process for explaining the manufacturing method of the present invention, and FIG. 5 is a completed sectional view of the present invention. Further, FIGS. 6 to 11 are cross-sectional views of the manufacturing process of a circuit board manufactured by a conventional manufacturing method. Code 1...Base, 2...Copper foil, 3...Aluminum foil, 4...
... Plating and etching resist ink, 5... Thick copper plating part, 6... Etching resist ink, 7.
... Dry film, 8... Insulating layer, 9... Protective film.

Claims (4)

[Claims] (1) A step of forming an etching resist on a desired portion of the dissimilar metal composite foil-covered insulating substrate and selectively etching only the upper metal foil of the dissimilar metal composite foil, and after peeling off the etching resist, the insulating substrate A step of pasting a dry film on the selected etched surface of the film to form a desired pattern and plating it with thick copper; and a step of etching the lower metal foil of the dissimilar metal composite foil after peeling off the dry film. A method for manufacturing a large current circuit board that can be wire bonded. (2) The method for manufacturing a large current circuit board according to claim 1, wherein the dissimilar metal composite foil is made of aluminum and copper. (3) The method for manufacturing a large current circuit board according to claim 1 or 2, wherein the upper metal foil of the dissimilar metal composite foil is aluminum. (4) The method for manufacturing a large current circuit board according to claim 1, wherein the insulating layer provided on at least one principal surface of the insulating substrate metal plate has good thermal conductivity.