JPH04159796A - Manufacture of metallic base wiring board - Google Patents

Abstract

PURPOSE:To precisely form a circuit pattern by forming conductor sections electrically connected with the surface of a metallic plate in holes and electrically connecting circuit conductors formed on the upper surface of an insulating layer and the conductor sections with the metallic plate through the conductor sections. CONSTITUTION:Conductor sections 7 are formed in interlayer connecting holes 6 exposed from an insulating layer 3 on the surface of a metallic plate 1. Then a resist pattern 11 is formed on the surface of an electroless plated layer 8 in such a way that a negative photosensitive resist 9 is applied to the surface of the layer 8 and the resist 9 is developed after the resist is exposed by putting a photomask 10 on the resist 9. After the pattern 11 is formed, circuit conductors 12 are formed by performing electrolytic plating to the layer 8 through the openings of the pattern 11. Therefore, a conductor circuit can be precisely formed, since the conductor sections 7 can accurately be formed to small sizes.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for manufacturing a metal-based wiring board.

[Background Art] In recent years, metal-based wiring boards, in which a metal plate and a metal foil such as copper foil are bonded together with an insulating adhesive, have been used instead of printed circuit boards in which copper foil is bonded to phenolic resin.

This is because metal-based wiring boards have characteristics such as good heat dissipation characteristics, good dimensional accuracy, and high mechanical strength, and meet the requirements for high-density mounting of electronic components.

However, compared to printed wiring boards using phenolic resin, metal-based wiring boards have a structure in which an insulating layer is sandwiched between a metal plate and metal foil, so stray capacitance is parasitic between the metal plate and metal foil. There is a problem in that circuit operation becomes unstable due to unnecessary coupling of signals due to this stray capacitance. This is a big problem especially in the case of high-frequency circuits, and has been an obstacle when applying metal-based wiring boards to high-frequency circuits.

In order to solve this problem, the ground portion of the circuit pattern formed on the metal foil may be electrically connected to the metal plate at an appropriate position. To do this, please refer to the following ■,■,
Method (2) has been used conventionally.

■ The first method is to pre-drill a hole in the metal foil and insulating layer at the point where you want to connect the ground part of the metal plate and the circuit pattern, fill this hole with solder or conductive paste, and use solder or conductive paste to is electrically connected to the ground part of the circuit pattern around the hole and the metal plate.

■ The second method is to drill a through hole in the metal base wiring board at the point where you want to connect the metal plate and the ground part of the circuit pattern, pass a metal bolt through this through hole, and then tighten the nut to the metal pole I. By tightening, the ground part of the circuit pattern and the metal plate are electrically connected.

(2) The third method is disclosed in Japanese Patent Publication No. 2-8472. This is done by, for example, printing a conductive adhesive on a metal plate by screen printing, drying it slightly, then applying an insulating adhesive mainly made of epoxy resin 17, and then drying it lightly to temporarily cure it. The metal foil is placed on top of the metal foil, the metal foil and the metal plate are crimped using a heat press, etc., the metal foil is etched to form a circuit pattern, and the conductive adhesive is used to connect the ground part of the circuit pattern to the metal plate. This is a method of electrically connecting boards.

[Problems to be Solved by the Invention] However, in the methods ① and ② above, the part for electrically connecting the ground part of the circuit pattern and the metal plate occupies a considerable amount of space, and the metal plate for high-density mounting It was difficult to manufacture the base wiring board.

Furthermore, in the method (2) above, since the conductive adhesive and the insulating adhesive are selectively printed by screen printing or the like, the printing position accuracy and dimensional accuracy of the conductive adhesive and the like are poor. For this reason, when a fine circuit pattern is formed by micromachining the metal foil, the conductive adhesive portion shifts from the ground portion of the circuit pattern, making it difficult to form a fine circuit pattern.

The present invention was made in view of the drawbacks of the conventional examples mentioned above, and its purpose is to enable good operation even in high-frequency circuits, enable high-density packaging, and improve the fineness of circuit patterns. An object of the present invention is to provide a method for manufacturing a metal-based wiring board that can be processed.

[Means for Solving the Problems] The method for manufacturing a metal-based wiring board of the present invention includes coating a photosensitive polymer material on one or both main surfaces of a metal plate to form an insulating layer, and then applying a photoresist. A step of forming a hole for interlayer connection in the insulating layer using a graphic technique, a step of forming a conductor part inside the hole for interlayer connection by electrolytic plating to make an electrical connection with the surface of the metal plate, and a step of forming a conductor part in the insulating layer and the conductor The method is characterized by comprising a step of forming a circuit conductor on the upper surface of the part and electrically connecting the circuit conductor and the metal plate via the conductor part.

[Function] If a metal-based wiring board is manufactured by the method of the present invention, the circuit conductor can be electrically connected to the metal plate through the conductor portion, so even in high-frequency circuits, instability of the circuit due to stray capacitance can be avoided. Is it possible to prevent this?

Moreover, since the interlayer connection holes are formed in the insulating layer by photolithography and the conductor portions are electrolytically plated inside the interlayer connection holes, very small conductor portions can be provided with good dimensional and positional accuracy. Therefore, fine processing of circuit conductors becomes possible, and high-density packaging using metal-based wiring boards becomes possible.

[Example] Hereinafter, an example of the present invention will be described in detail based on FIGS. 1(a) to (+).

First, a metal plate 1 such as an aluminum plate having a thickness of 1 mm was prepared. Next, an epoxy resin 2 containing a cationic photoinitiator (latent curing agent) that generates a Lewis acid when irradiated with ultraviolet rays is applied as a photosensitive organic polymer material to the entire upper surface of the metal plate 1. , an insulating layer 3 on one side of the metal plate 1
was formed (Fig. 1(a)). Next, the area where the conductor portion 7 on the two sides of the metal plate 1 is to be formed is covered with a mask 4,
Epoxy resin 2 by ultraviolet lamp 5 through mask 4
was exposed to light to cure the exposed area (FIG. 1(b)), and then developed. Since the unexposed areas of the epoxy resin 2 are removed during development, the insulating layer 3 is removed using photolithography technology.
An interlayer connection hole 6 is opened at a desired position (see FIG. 1(C)).
)). After forming the interlayer connection holes 6 in the insulating layer 3, the metal plate]
When electrolytic plating is applied to the upper surface of the metal plate 1, a conductor portion 7 is formed on the surface of the metal plate 1 inside the interlayer connection hole 6 exposed from the insulating layer 3 (FIG. 1(d)). Copper is the most suitable material for plating the conductor portion 7, as it has low resistivity and excellent high frequency characteristics. Thereafter, electroless copper plating is applied to the surfaces of the insulating layer 3 and the conductor portion 7 to form an electroless plating layer 8 having a thickness of submicron or less (Fig. 1(e)).
. Next, a negative type photosensitive resist 9 is coated on the electroless plating layer 8 (FIG. 1(f)), a photomask 10 is placed over the photosensitive resist 9, and exposed to light (FIG. 1(f)).
g)) Further development is performed to form a resist pattern 11 on the electroless plating layer 8 (FIG. 1(h)). In addition,
The method for forming the resist pattern 1 may be any one of screen printing, dry film, and photolithography, which can be selected depending on the resolution required for the resist pattern 11. moreover.

Electrolytic plating is applied to the second part of the electroless plating layer 8 through the opening of the resist pattern 11 to form the circuit conductor 12 (Fig. 1-(i)). After the circuit conductors 12 are formed, the resist pattern 11 is removed (FIG. 1(j)), and the exposed portions of the thin electroless plating layer 8 are etched away using an etching solution such as ammonium persulfate, thereby forming a gap between each circuit conductor 12. It was separated (FIG. 1(k)) to obtain the desired metal base wiring board 13. In addition, in FIG. 1 (1), electronic components 14.15 such as IC chips, resistors, capacitors, inductors, transistors, etc. are placed on the circuit conductor 12 of the metal base wiring board 13, and the terminals of the electronic components 14.15 and A state in which the circuit conductor 12 is wire-bonded or soldered is shown.

If manufactured in this way, the metal plate 1 and the ground part of the circuit conductor 12 can be easily electrically connected by the conductor part 7, thereby preventing circuit instability caused by stray capacitance even in high frequency circuits. be able to. Moreover, since the conductor portion 7 can be made smaller than the line width of the circuit conductor 12, the space efficiency of the board is improved, and a metal-based wiring board for high-density mounting can be manufactured. Furthermore, since the conductor portion can be made smaller, there are fewer restrictions on the placement position of the conductor portion, and the circuit conductor can be connected to the metal plate at any location. Furthermore, since the conductor portion 7 can be small and provided with high precision, fine processing of the conductor circuit is also possible, and mass productivity is also improved.

In Figure 1, the circuit conductor is provided only on one side of the metal plate, but it is also possible to provide an insulating layer and a circuit conductor on both sides of the metal plate and electrically connect the circuit conductors on both sides to the metal plate through the conductor part. good.

[Effects of the Invention] If a metal-based wiring board is manufactured by the manufacturing method of the invention, instability of the circuit due to stray capacitance can be prevented even in high-frequency circuits.

Moreover, the conductor part that electrically connects the metal plate and the circuit conductor can be formed small and with high dimensional accuracy, making it easier to microfabricate the circuit conductor and allowing for higher-density mounting on the metal base. Can produce wiring boards.

[Brief explanation of drawings]

FIGS. 1(a) to 1(1) are cross-sectional views illustrating the method for manufacturing a metal-based wiring board of the present invention. 1...Metal plate 3...Insulating layer 6...Interlayer connection hole 7...Conductor portion 12...Circuit conductor Patent applicant Murata Manufacturing Co., Ltd. Agent Patent attorney Masafusa Nakano

Claims (1)

[Claims] (1) After coating a photosensitive polymer material on one or both main surfaces of a metal plate to form an insulating layer, forming holes for interlayer connection in the insulating layer using photolithography, and electrolysis. forming a conductor part inside the interlayer connection hole by plating and electrically connecting it to the surface of the metal plate; forming a circuit conductor on the upper surface of the insulating layer and the conductor part; and connecting the circuit conductor and the metal plate to the surface of the metal plate. 1. A method for manufacturing a metal-based wiring board, comprising the step of electrically connecting via a conductor portion.