JPH01295485A - Manufacture of printed wiring board with thick plate conductor - Google Patents

Abstract

PURPOSE:To improve circuit precision, by performing etching in two or more stages at the time of forming the circuit of a thick plate conductor, and forming a resist film on also the side wall of a circuit forming part by electro-deposition before a second etching. CONSTITUTION:For the conductor 2 of a substrate 1 with thick plate conductor wherein the conductor 2 of 200mum or more in thickness and a base substrate 4 are laminated in a body, the flowing are performed in two or more stages, the forming of a resist film 5, etching, and the exfoliating process of the resist film 5. When the resist film 5 is formed in a second stage or the later stage, a photo-sensitive resist film 5a is formed on the whole surface of the conductor 2 by electro-deposition; then the plane part of a circuit forming part 2a left by the etching in the preceding stage and its side wall only are exposed, and the part which is not yet exposed to light is exfoliated; the etching and the exfoliating of the resist film 5a are repeated by using the part exposed to light as a mask. As a result, if the conductor thickness increases, the precision of circuit formation can be kept in the range within about 100mum, thereby forming a thick plate conductor circuit of high precision.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of manufacturing a printed wiring board having a thick plate conductor circuit.

[Conventional technology]

In Figure 2, which is a cross-sectional view of the metal base substrate,
The metal base substrate (1) includes a conductor (2) such as copper foil or aluminum-copper composite gold foil, and an insulating layer (3) formed of epoxy resin-glass cloth or a mixture of epoxy resin and inorganic filler. It is integrally formed with a base metal (4) such as aluminum or copper plate. The thickness of the net portion of the conductor (2) was approximately 70 .mu.m or less, and at most 100 .mu.m, as shown in Japanese Patent Application Laid-Open No. 176188/1983. A circuit is formed on this metal base substrate (1) by etching to form a metal base printed wiring board, which takes advantage of its excellent heat dissipation and dimensional stability, and is used as a printed wiring board for inverter control devices such as power modules. There is.

In recent years, with the expansion of applications of inverter control devices and their improved functionality, there has been a need to increase current capacity, and it is impossible for printed wiring boards to meet this demand by increasing circuit width and board size. , it is necessary to take measures depending on the circuit thickness.

Conventionally, when forming a circuit on a board (1) with five conductors (2) and a thickness of up to 100 μm, as shown in Fig. 3(a), first the conductor (2)
A resist film (5) is formed on the surface with a predetermined width and shape.

The resist film (5) is provided by applying resist ink by screen printing, using a photosensitive film, or the like. Then, as shown in FIG. 3(b), a ferric chloride aqueous solution,
The portions other than those protected by the resist film (5) are removed using an etching solution such as a cupric chloride aqueous solution or a sulfuric acid-hydrogen peroxide aqueous solution, and a circuit is formed as shown in FIG. 3(c) to form a printed wiring board. I am getting .

On the other hand, as shown in Japanese Unexamined Patent Publication No. 62-176188, in order to obtain a thick plate conductor circuit, there is an example in which a predetermined circuit is formed by etching, and then a thick layer of copper is further applied by thick plating. be.

[Problem to be solved by the invention]

However, in the conventional method for manufacturing printed wiring boards as described above, the copper foil is polished by the etching solution from both the thickness direction and the horizontal direction on all surfaces that do not come into contact with the etching solution due to the resist film (5). As the copper foil becomes thicker, the side etching becomes larger as shown in Figure 3(d), the etching time becomes longer, and the resist film (5) is also attacked by the etching solution. The surface of the copper foil was also melted, and not only the cross section of the circuit but also the surface and IIA#A changed, making it impossible to form a usable circuit. Therefore, in the above method, the limit was that the thickness of the copper was less than 200 μm. It has also been proposed to thicken copper by plating after forming a circuit by etching, but there is a limit to how thick the copper can be thickened by plating, and there may be problems with reliability regarding the adhesion of the plated portion.

In order to eliminate the above-mentioned drawbacks, the present invention aims to provide a method for manufacturing a printed wiring board with a thick plate conductor, which can prevent side etching and form a thick plate conductor circuit with high conductor circuit accuracy. purpose.

[Means to solve the problem]

The method for manufacturing a printed wiring board with a thick plate conductor of the present invention includes resist film formation, etching, and resist film formation on a conductor having a thickness of 200 μm or more and a conductor of a thick plate conductor-attached board in which a base substrate is integrally laminated. The stripping process is performed in two or more times, and in the second and subsequent resist film formation, a photosensitive resist film is formed on the entire surface of the conductor by electrodeposition, and then
This is a method in which only the plane portion of the circuit forming portion remaining from the previous etching and its sidewall portions are exposed to light, the unexposed portion is peeled off, and the exposed portion is used as a resist film to repeat etching and resist film peeling.

[For production]

In the present invention, as the thickness of the conductor increases, it is side-etched by an etching solution, as shown in FIG. 3(d).
In order to prevent this, the first etching is carried out to the conventional conductor thickness of about 100 μm, and from the second etching onwards, the electrodeposition liquid is By forming a photosensitive resist film using a photosensitive resist solution, exposing it to light, peeling it off, and performing subsequent etching and resist film peeling, even if the conductor thickness increases, the circuit remains intact. The accuracy of the formation can always be maintained as with conductor thicknesses of the order of 100 μm.

As mentioned above, etching of a thick plate conductor is performed simultaneously in the thickness direction and the side direction, so as the thickness increases, the slope between the width of the surface part of the conductor and the bottom part (the side in contact with the M edge) increases. If the pattern becomes large, the circuit width accuracy cannot be maintained, so etching can be performed two or more times to reduce the slope. In addition, by protecting the sidewalls of the circuit forming portions remaining from the first etching with a resist film,
Side etching can be prevented in the second and subsequent etchings. Furthermore, by adopting an electrodeposition method as the method of forming the resist film from the second time onward,
A resist film can be easily and reliably formed, and unlike printing methods, techniques and skills are not required to improve printing accuracy.

〔Example〕

Examples of the present invention will be described below. Thickness 250μ
Insulating layer (hereinafter simply referred to as copper plate) of oxygen-free rolled copper plate (hereinafter simply referred to as copper plate)
3) By cathodic treatment of the surface in contact with Rz=2~5μ
The four bodies (2) are roughened to a roughness of m, and the insulating layer (3) is
0 and 1 made of glass cloth and epoxy resin as materials
A prepreg with a thickness of 5 mm was used, and a base metal (4 mm) was used.
) A copper plate with a thickness of 3n+m was used.

These were laminated as shown in FIG. 2 and press-molded to obtain a metal base substrate (1).

100mm x 50m from this metal base board (1)
In order to obtain a metal base printed wiring board with a thick plate conductor having external dimensions of m and a conductor pattern (not shown) in which conductors of 3.0 mm width are arranged at intervals of 2.0 mm, the method shown in FIG. The circuit was formed using

FIG. 1 is a sectional view showing the method of the embodiment. First, after covering the exposed surface of the base metal (4) with a vinyl chloride-based protective film, as shown in Figure 1 (a), the thick plate conductor (2) is
5 resist ink S-40 (manufactured by Taiyo Ink KK)
Width 3. A resist film (5) was obtained by printing with a 200-mesh screen plate so as to have a thickness of 15 μm and a thickness of 15 μm. This was dried in an oven at 80°C for 20 minutes, and the first etching was performed using an aqueous ferric chloride solution.

Etching was performed by spraying at 40° C. for 5 minutes. The etching depth of the copper plate at this time was approximately 100 μm. This state is shown in FIG. 1(b). Thereafter, the resist film (5) was peeled off in a 2% aqueous solution of caustic soda, and the resist film (5) was peeled off in a 2% aqueous solution of caustic soda.
C) was obtained. The line width of conductor (2) at this time was 3.0 m@.

Next, the conductor (2) surface of the substrate that had undergone the first etching was applied with a DC voltage of 15 mL in an ultraviolet curable photosensitive electrodeposition liquid Sonne EC-UV (Kansai Paint Co., Ltd. Il, trademark).
The uncured electrodeposited resist film (
5a) was formed. Then, a film that allows light to pass through only the plane and side surfaces of the circuit forming portion (2a) remaining from the first etching is prepared, placed on the electrodeposited resist film (5a), and irradiated with ultraviolet rays at 30 millijoules. , exposed to light. By washing this with water, the uncured portion is removed while leaving the cured portion, and as shown in FIG. formed. In response to this, a second etching was performed. Using the same ferric chloride solution as the first time, spray etching at 40°C for 8 minutes.
Etching to a depth of 50 .mu.m was completed and the state shown in FIG. 1(f) was obtained. The electrodeposited resist film (5a) was removed from this using a 2% aqueous solution of caustic soda, and the resist film (5a) was further punched into a predetermined shape with four dimensions. ) has a cross section, as shown in Figure 3(d).
A metal base printed wiring board with a thick plate conductor was obtained which had a highly accurate and practical circuit which was significantly different from the cross section of the conductor (2) formed by the single process.

Note that the present invention is not limited to the embodiments described above, and can be applied to double-sided boards such as metal core boards, ceramic boards, general glass cloth-epoxy resin boards, etc. with thick board conductors, as long as circuits are formed on thick plate conductors. It can also be applied to substrates. In these cases, it is necessary to take into account in advance warpage and deformation caused by the type, thickness, and consistency of thermal expansion coefficients of the insulating layer and base metal associated with the thick plate conductor.

The present invention is also extremely effective for composite conductors made of dissimilar metals such as aluminum/copper, and when there are problems such as differences in solubility in etching solution and dissolution rate encountered when etching a dissimilar metal combination conductor. In this case, by forming the resist film for the second time, it is possible to protect the conductor in the circuit formation area after the first etching, so that the effect can be further improved.

〔Effect of the invention〕

As described above, according to the present invention, when forming a circuit on a thick plate conductor, etching is performed in two or more times, and before the second etching, a resist film is also formed on the side wall of the circuit forming part by electrodeposition. This makes it possible to prevent excessive etching on the side of the circuit forming part, easily obtain circuit accuracy equivalent to the conventional circuit accuracy in the case of a conductor thickness of 100 μm or less, and realize stable high current with a thick plate conductor. A printed wiring board with a thick conductor having a capacitance can be manufactured.

[Brief explanation of the drawing]

FIGS. 1(a) to (g) are cross-sectional views showing the steps of an embodiment of the present invention, FIG. 2 is a cross-sectional view showing a metal base substrate, and FIGS. It is a sectional view showing a process. In each figure, the same reference numerals indicate the same or corresponding parts, (1)
is a metal base substrate, (2) is a conductor, (2a) is a circuit forming part, (3) is an insulating layer, (4) is a base metal, (5), (
5a) is a resist film.

Claims (1)

[Claims] (1) For a conductor with a thickness of 200 μm or more and a conductor of a substrate with a thick plate conductor that is integrally laminated with a base substrate, the steps of resist film formation, etching, and resist film peeling are performed in two or more times, When forming the resist film for the second and subsequent times, after forming a photosensitive resist film on the entire surface of the conductor by electrodeposition, only the plane part of the circuit forming part and its side wall part remaining from the previous etching are exposed to light to remove the unexposed part. A method for manufacturing a printed wiring board with a thick plate conductor, characterized by repeating peeling, etching using a photosensitive part as a resist film, and peeling off the resist film.