JPS60176293A - Method of producing printed 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 The present invention relates to a method for manufacturing a printed wiring board that prevents electrolytic corrosion reaction between through holes caused by the metal forming the through holes.

BACKGROUND OF THE INVENTION With the recent development of the electronic equipment field, the pursuit of smaller size, lighter weight, and higher reliability has become active in the consumer electronic equipment field as well. Similar to electronic devices, printed wiring boards are becoming more densely wired and mounted, and double-sided through-hole circuit boards are now increasingly being used. especially,
In the field of consumer equipment, unlike the field of industrial equipment, issues include not only reliability but also price and mass productivity.

Normally, the through-holes of a through-hole circuit board are made conductive by copper plating, but now a method of making the through-holes conductive is using conductive paint, which is cheaper and easier to mass-produce.

However, the method of manufacturing the printed wiring board has the following problems. In other words, the conductive layer of the through-holes formed with conductive paint causes an electrolytic corrosion reaction between the through-holes due to the potential difference between the multiple through-holes and the humidity and temperature around the through-hole substrate, causing the through-holes with a high potential to become oxidized by the through-holes with a low potential. The ionized metal in the conductive paint moves toward the through-holes and dissolves into the electrical insulation layer of the printed circuit board, eventually causing a short circuit between the through-holes. Various methods have been proposed to prevent this electrolytic corrosion reaction, but none are perfect.

An object of the present invention is to provide a method for manufacturing a printed wiring board that prevents electrolytic corrosion reactions between through holes.

The details of the present invention will be explained using the drawings.

First, a through hole 3 is made at a desired position in a double-sided steel-clad laminate having copper foils 2-a12-b on both sides through an electrically insulating layer 1 (FIG. 1). After that, an electroless nickel plating layer 4 is deposited on the wall surface of the through hole 3 (Fig. 2), and then the copper foils 2-a and 2-b of the double-sided copper-clad laminate are etched using a conventional etching method or the like. The desired circuits are set as 2'-a and 2'-b (Fig. 3). Thereafter, a conductive paint layer 5 containing metal powder as a main component is provided on the electroless nickel plating layer 4 to impart electrical continuity reliability to the through-holes, thereby obtaining a through-hole circuit board. The details of the present invention are a method for manufacturing a printed wiring board as described above.

In Fig. 2, an electroless nickel plating layer 4 is provided on the wall surface of the through hole 3, but this is intended to take advantage of the property of metallic nickel that is extremely resistant to electrolytic corrosion reactions, that is, as shown in Fig. 4. Providing the electroless nickel plating layer 4 on the base of the conductive paint layer 5 whose main component is metal powder as shown above prevents the electrolytic corrosion reaction of the conductive paint whose main component is metal powder between the through-holes. be.

In addition, if the thickness of the electroless nickel plating layer 4 is about 0.4μ, the electrolytic corrosion reaction of metal powder used in conductive paint will not occur, but the electrolytic corrosion reaction will occur depending on the thickness of the nickel plating layer. The relationship in occurrence varies depending on the plating conditions of the electroless nickel plating layer, so it is not particularly limited. However, the conductive paint may be used to fill the entire through hole.

Next, the present invention will be explained in detail.

Example First, drill holes for through-holes were formed in a commercially available glass cloth-based epoxy resin double-sided copper-clad laminate having a thickness of 1.6 fins.

Next, electroless nickel plating was applied to the through holes using the electroless nickel plating process of Sibley First ■. In other words, after drilling a hole, the inside of the hole is cleaned using a high-pressure cleaning device, and the hole is cleaned at a 55° angle for the purpose of degreasing the board.
Immerse for 5 minutes in cleaner PM-900 kept warm at C.
Next, etch PM-940 for 14. 3 pu of water, sulfuric acid (66
Baume) 0.5.6. Immerse in an acidic surface conditioning solution prepared at a ratio of 1,8 ky of chromium trioxide at a temperature of 60°C for 5 minutes, then apply 9F (catalyst) to 1! , water Q, 751, and hydrochloric acid 0.25A in the ratio of catalyst and liquid temperature 20
5 minutes at 45 °C and then immersed in a 10% (by volume) diluted Cubozit accelerator for 2 hours at a liquid temperature of 45 °C.
After soaking for a minute, keyposite electroless nickel PM-
Electroless nickel plating solution with a ratio of 980 to 6 J of water and pH adjusted to 9 with ammonium hydroxide at a temperature of 3.
Immerse at 0"C for 10 minutes and apply a layer of 0.4mm to the through-hole wall.
An electroless nickel plating layer of μ was obtained. Next, the copper foil of the double-sided steel-clad laminate was etched away using cupric chloride so as to form a desired circuit. Furthermore, a conductive paint containing silver powder as a main component was applied on the electroless nickel plating layer, and then the conductive paint was cured at 130°C for 3 hours, as shown in Figure 5, and the number of through holes was 2. The through-hole spacing is 2.5 m, the through-hole diameter is 0.9 w * the through-hole land outer diameter is 1.2 m, and the two through-holes are not electrically connected.

Comparative Example A drill hole for a through hole was formed using the same double-sided copper-clad laminate as in the example. Next, the copper foil of the double-sided copper-clad laminate was removed by etching using cupric chloride so that it became the same as the circuit of the example, and then the electroless nickel plating layer was not provided, but the other steps were the same as in the example. A conductive paint layer containing silver powder as a main component was provided on the through-hole wall to obtain a through-hole circuit board.

The circuit boards obtained in Examples and Comparative Examples were processed under the following test conditions, and changes over time in insulation resistance between through-holes were measured.

Processing: 60"C90%FLH Applied voltage: 40V(1)O) Figure 6 shows the test results.

As is clear from FIG. 6, in the through-hole circuit board obtained by the present invention, the electrolytic corrosion reaction between the through-holes is prevented.
In addition to significantly improved reliability, the present invention is cheaper and more easily mass-produced than the conventional manufacturing method for copper through-hole plated circuit boards, as conduction through the through-holes is achieved by applying conductive paint. Therefore, it is judged that the industrial value of the present invention is extremely large.

[Brief explanation of drawings]

1 to 4 are cross-sectional views of main parts showing the manufacturing process of a printed wiring board using the pressure of the present invention; FIG. 5 is a plan view of a test pattern for confirming the occurrence of an electrolytic corrosion reaction on a printed wiring board; FIG. 6 is a curve diagram showing changes over time in insulation resistance between through-holes of printed wiring boards obtained in Examples of the present invention and Comparative Examples. l is an electrical insulating layer, 2-a, 2-b are copper foils, 2'-a, 2
'-b is a circuit, 3 is a through hole, 4 is a nickel plating layer, 5 is a conductive paint layer

Claims (1)

[Claims] Form through-holes at desired positions on the double-sided copper-clad laminate,
After that, electroless nickel plating is deposited on the wall surface of the hole, unnecessary parts of the copper foil of the double-sided copper-clad 9-layer board are removed to form a predetermined circuit, and then metal powder is deposited on the electroless nickel plating layer of the through hole. A method for manufacturing printed wiring boards characterized by forming a conductive paint layer whose main component is