JPS60187094A - Method of producing through hole circuit board - 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 the Invention The present invention relates to a method for manufacturing through-hole wiring boards used in general electronic equipment such as video tape recorders and televisions.

Conventional configurations and their problems In recent years, as the demand for smaller, lighter, and more reliable electronic equipment has increased, the demand for through-hole wiring boards has been increasing.

This through-hole wiring board electrically connects wiring circuit conductors formed on both the front and back surfaces of an insulating substrate by making the holes that pass through both conductive. Various methods have been used to manufacture this board. It has been implemented.

A typical manufacturing method thereof is through the manufacturing steps shown in FIGS. 1A to 1G.

That is, first, using a so-called double-sided copper-clad laminate in which copper is adhered to the entire front and back surfaces of an insulating substrate 1 made of glass epoxy, paper phenol, etc. as shown in FIG. As shown in Fig. 1B, a through hole 3 is drilled at a predetermined position where connection is required, and then, as shown in Fig. 1C,
This substrate is immersed in an activation treatment solution consisting of an acidic hydrochloric acid solution of stannous chloride and palladium chloride to contain the inner wall surface of the through hole.

After depositing an activation layer 4 consisting of fine particle nuclei of palladium on the entire surface of the substrate, as shown in the first diagram, this substrate is immersed in an electroless copper plating solution consisting of an alkaline solution of copper complex salt and formalin to form through holes. Metallic copper 5 is deposited on the inner wall surface and the entire surface of the substrate, and further, as shown in FIG. 1E, electrolytic copper plating is performed to deposit metallic copper 6 to increase the conductor thickness.

Then, as shown in FIG. 1F, the through holes 3 and the wiring circuit are covered with an etching-resistant mask 7, and unnecessary copper is dissolved by immersing it in a ferric chloride solution or a cuprous chloride solution. By removing it, a through-hole wiring board with conductive through-holes as shown in FIG. 1G is made.

However, the through-hole wiring board manufactured by this method has the following drawbacks.

■ This manufacturing method requires wet processes such as activation treatment and electrolytic copper plating, which requires large-scale equipment for waste liquid treatment.

■ The manufacturing process is complicated, including activation treatment, plating treatment, and punching, and it lacks economic efficiency.

(2) When a fairly thick copper layer is formed by plating and then a circuit conductor layer is formed by photoetching, lines in the circuit conductor layer tend to thin due to side etching, making it difficult to form fine wiring patterns.

■ Because the metal conductor layer is formed directly on the wall of the through hole,
The reliability of through-hole connections is greatly affected by the material of the insulating substrate used. Paper-based phenol substrates in particular have a large coefficient of thermal expansion, so the metal conductor layer cannot follow the expansion and contraction of the substrate, resulting in through-hole connections. Connection becomes less reliable.

■ In the electroless copper plating process, the deposition state of the plating is easily affected by the material of the insulating substrate and trace amounts of impurities contained in the insulating substrate. In particular, the plating is difficult to adhere to Teflon and polyimide substrates, which still contain impurities such as sulfur. This significantly inhibits the deposition of electroless copper plating, making it difficult to make good through-hole connections.

■ Activation treatment is performed by immersing the entire board with holes drilled in the processing solution, so a conductor layer is formed on the side walls around the insulating substrate and through holes that do not require conductivity. You need to do it twice.

A through-hole wiring board that eliminates the drawbacks of the conventional examples described above can be obtained by, for example, forming a circuit conductor layer directly on an insulating substrate using only electroless copper plating, and using an additive method or an etching method to make through-hole connections. Although methods such as filling silver paste into holes penetrating the wiring circuit conductor layer and making through-hole connections have been implemented, none of these methods solves all of the above-mentioned drawbacks.

OBJECTS OF THE INVENTION In view of the above-mentioned drawbacks, an object of the present invention is to provide a manufacturing process that is relatively simple and economical, minimizes side etching to facilitate fine wiring, and improves the reliability of through-hole connections. It is an object of the present invention to provide a method for manufacturing a through-hole wiring board that can be significantly improved.

Structure of the Invention In order to achieve the above object, the through-hole wiring board of the present invention forms wiring circuit conductor layers on both the front and back surfaces of an insulating substrate,
Provide a hole that penetrates the wiring circuit conductor layer that requires connection,
After applying a conductive resin to the inner wall of the through hole and forming an insulating resist film on both the front and back surfaces of the insulating substrate so that a part of the wiring circuit conductor layer around the through hole is exposed, the inner wall of the through hole is coated with a conductive resin. It is made by depositing a conductive metal layer on the conductive resin layer and the exposed wiring circuit conductor layer by electroless plating.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIGS. 2A to 2E are cross-sectional views of essential parts of a printed wiring board in each manufacturing process for understanding the method of manufacturing a through-hole wiring board according to an embodiment of the present invention.

The through-hole wiring board according to the present invention first has a desired wiring circuit conductor layer 9 on both the front and back surfaces of an insulating substrate 8, as shown in FIG. 2A. form cl.

In this embodiment, the insulating substrate 8 includes two paper base phenol resins, two paper base epoxy resins, two paper base polyester resins, a glass base epoxy resin, a glass base Teflon resin,
Glass base polyimide resin.

A synthetic resin substrate such as a composite resin or a metal substrate made of aluminum or iron that is insulated with epoxy resin or the like is used, and the entire front and back surfaces of these various insulating substrates 80 are coated with metal such as copper foil <9 A double-sided copper-clad laminate is made by gluing .9', and using this copper-clad laminate, the unnecessary parts of the copper on both the front and back sides of <9.9' are dissolved by a known method such as photo-etching. As a result, desired wiring circuit conductors 9.9' made of copper foil were formed on both the front and back surfaces of various insulating substrates 8.

Next, as shown in FIG. 2B, wiring circuit conductor layers 9 that require connections formed on both the front and back surfaces of the insulating substrate 8. A through hole 1o having a predetermined diameter is punched using a punching method using a drill or a mold, and as shown in FIG. A conductive resin 11 having a certain degree of conductivity was coated on a part of the substrate and cured by heating. The conductive resin 11 used in this step is gold, silver, copper, iron, and tin.

It has a relatively low viscosity and is made by uniformly mixing and dispersing fine metal powder made of zinc, nickel, or their alloys in a thermosetting synthetic resin. It must serve as a catalyst nucleus for electrolytic plating.

In addition, the synthetic resin material to be mixed must have excellent adhesion to the insulating substrate used, sufficient resistance to electroless plating, and not contain any impurities that would interfere with the electroless plating reaction. In this example, as a synthetic resin that meets these purposes, an amine-based or imidazole-based acid anhydride-based epoxy resin was selected as a curing agent, and flaky silver and copper powder was added to this resin as a metal powder. A conductive resin mixed at a weight ratio of about 60 to so% was prepared, and this conductive resin was applied to the inner wall surface of the through hole by a silk screen method or a pin contact method.

In this case, it is necessary to prevent the through-hole from clogging with conductive resin, but the method for doing this is to lower the viscosity of the conductive resin as much as possible, fill the through-hole, and then use a compressor to seal the through-hole. An effective method is to blow strong wind.

Then, as shown in the second diagram, the wiring circuit conductor layer 9 in the through hole 10 and its surrounding area. An insulating resist film 12 is formed by selectively applying an insulating resist made of a chemical-resistant resin material to both the front and back surfaces of the insulating substrate so that a portion of cl is exposed, and curing the resist.

The insulation resist 12 used in this process needs to have sufficient resistance to the electroless plating treatment in the next process, but it also needs to serve as a heat-resistant resist. Excellent properties are required in terms of strength and insulation resistance.

In this example, as an insulating resin material that meets this purpose, we used a mixture of epoxy resin or acrylic resin with an inorganic filler such as alumina or silica, or a dry film obtained by modifying epoxy resin and acrylic resin. use,
Desired resist turns were formed using a screen printing method and a photo method, respectively.

Note that the step of forming the insulating resist film may be performed not after forming the conductive resin film on the wall of the through hole, but immediately after forming the through hole.

The substrate on which the insulating resist film 12 has been formed at the necessary locations of the wiring circuit conductor layers 9, 9' in this way is immersed in an electroless copper plating solution, and as shown in FIG. Layer 11 and its surrounding wiring circuit conductor layer 9. A conductive metal layer 13 made of metallic copper is deposited on σ.

For electroless copper plating in this step, a plating bath with the following composition is used, and by maintaining the pH at 12.5 to 13.0 and soaking for 3 to 5 hours, a 6 to 10 μ thick [electroless plating bath] Copper sulfate 7-8y/2 EDTA 10-169/It Caustic soda 8-10P/Il Formalin 3-6ml/n of copper was precipitated.

As described in detail, the through-hole wiring board according to the present invention has the following features:
A wiring circuit conductor layer is formed by etching copper foil adhered to both the front and back surfaces of an insulating substrate, a hole is made through both, a conductive resin layer is formed on the inner wall surface, and then a conductive resin layer is formed on the inner wall surface. It is made by performing electroless copper plating to deposit a conductive layer made of metallic copper on the through hole and the wiring circuit conductor layer around the through hole.

Therefore, the through-hole wiring board according to the present invention has the following effects compared to the conventional example.

■ No electrolytic plating process is required, and the activation process for making the through-holes conductive is performed by a dry process using conductive resin, which simplifies the manufacturing process and requires no large-scale manufacturing equipment. does not require.

(2) Since conductive resin can be selectively applied only to the through-holes that require conductivity, only one hole-machining process is required, reducing the number of man-hours.

■ Since the insulating substrate surface exposed on the inner wall surface of the through hole is completely covered with conductive resin, impurities that act as catalyst poisons contained in the insulating substrate during the electroless copper plating process seep out, and the characteristics of the deposited copper are affected. Good conductivity is obtained even for insulating substrates made of The reliability of through-hole connections against expansion and contraction of the insulating substrate due to cycles is extremely high.

■ Since the wiring circuit conductor layer is formed by etching a relatively thin metal foil (copper foil), there is less narrowing of the circuit conductor width due to side etching, and a high-density through-hole wiring board with fine wiring can be obtained. It will be done.

[Brief explanation of the drawing]

Figures 1A-G are cross-sectional views of main parts of a printed wiring board in the main manufacturing process to explain the manufacturing process of a conventional through-hole wiring board, and Figures 2A-E are through-holes in an embodiment of the present invention. FIG. 3 is a cross-sectional view of a main part of a printed wiring board in a main manufacturing process for explaining a method for manufacturing a wiring board. 8...Insulating substrate, 9. V... Wiring circuit conductor layer, 10... Through hole, 11... Conductive resin layer, 12... Insulating resist film, 13...
...Conductive metal layer (electroless copper layer).

Claims (1)

[Claims] 0) A step of forming a wiring circuit conductor layer on both the front and back surfaces of an insulating substrate, a step of providing a hole penetrating the wiring circuit layer that requires the connection, and a step of forming a conductive resin on the inner wall surface of the through hole. a step of forming an insulating resist film having electroless plating resistance at a predetermined position on both the front and back surfaces of the insulating substrate so that a part of the wiring circuit conductor layer around the through hole is exposed; A method for manufacturing a through-hole wiring board, comprising the step of depositing a conductive metal layer by electroless plating on the through-hole and the wiring circuit conductor layer around the through-hole. (2) The wiring circuit conductor layer formed on both the front and back surfaces of the insulating substrate is formed by an etching method that selectively dissolves and removes unnecessary parts of the metal foil. A method for manufacturing a hole wiring board.