JPH01253990A - Printed circuit board - Google Patents

Abstract

PURPOSE:To obtain a printed circuit board having a solder resist to be formed with a fine circuit pattern and high heat resistance and chemical resistance by providing a through hole and an electroless plating layer on the uppermost layer of the conductor layer of a wiring pattern. CONSTITUTION:A through hole 1 and a conductor layer of a wiring pattern 2' are formed by sequentially forming first electroless copper-plated layer 4 on the upper faces of a copper foil 3 applied on both sides faces of an insulation board 8 and the inner wall face of a hole opened at the board 8, an electroless plating layer 5 on the upper face of the layuer 4, a second electroless plating copper-lating layer 6 on the layer 5, and then etching it to have a predetermined conductive pattern. Thus, the adhesive properties of the conductive layer to etching resist are improved, and the adhesive properties of a wiring pattern 2 to a solder resist 7 are improved. Thus, a fine circuit pattern can be formed, and the heat resistance and chemical resistance of the resist 7 are improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to printed wiring boards, and particularly to through holes and wiring patterns.

[Conventional technology]

As shown in FIG. 2, the conductor layer of the through-holes and wiring nozzles of a conventional printed wiring board has a structure in which, for example, an electroless button 5 is plated on the upper surface of an In14 plated with % copper.

[Problem to be solved by the invention]

Since the above-mentioned conventional printed wiring board has a smooth surface because the uppermost layer of the conductor layer is an electroplated layer, it has the following drawbacks.

1. When forming an etching resist, it was difficult to form a fine circuit pattern because the adhesion strength between the etching resist and the conductive layer could not be maintained.

2. Because the adhesion strength between the solder resist and the conductor layer cannot be maintained, the heat resistance, kettle resistance, and bath agent resistance of the solder resist are poor.

3. Soldering is poor when mounting components.

The object of the invention is to provide a printed wiring board that can form a fine circuit pattern, has a solder resist with good heat resistance and needle quality, and has good soldering properties.

[Means to solve the problem]

The printed wiring board of the present invention has no through-holes or the uppermost layer of the conductor layer of the wiring pattern. A deplating layer is provided.

〔Example〕

Next, one embodiment of the present invention will be explained with reference to the drawings.

FIG. 1 is a longitudinal sectional view of an embodiment of the present invention.

The conductor layer of the through hole 1 and the wiring pattern 2' (including the pad 9) is formed by forming a first conductor layer on the upper surface of the copper foil 3 stretched on both sides of the insulating substrate 8 and on the inner wall surface of the hole drilled in the insulating substrate 8. An electroless copper plating layer 4 is formed with a thickness of 2 to 5 μm, and the first
Electrolytic copper plating layer 5 is placed on the top surface of electroless copper plating layer 4 for 20 minutes.
A second electroless copper plating layer 6 is formed on the upper surface of the electrolytic copper plating layer 5 to a thickness of 2 to 5 μm, and then etched into a predetermined conductive pattern. Well formed. Thereafter, a printed wiring board is obtained by forming a solder resist 7.

In this example, when forming a wiring pattern with a width of 150 μm, the disconnection rate of the thin line pattern was reduced from 5% in the conventional printed wiring board to 2%, and the yield was increased. Improved.

Furthermore, as shown in Table 1, the soldering properties were also improved.

Table 1 Reflow conditions: 150'090 seconds, 235'020 seconds Soldering conditions: 238'03 seconds Number of samples = 15 pieces (Number of through holes: 1563 holes/sheet Number of pads: 2162 pieces/sheet) As shown in Table 1. It can be seen that the printed wiring board according to the present invention has excellent soldering properties even after heat treatment such as reflow.

〔Effect of the invention〕

As explained above, the present invention has an electroless plating layer as the uppermost layer of the conductor layer of the through-hole and wiring pattern, so when forming the wiring pattern by etching, the adhesion between the conductive layer and the etching resist is improved. Because of its good properties, it can be formed at high density. This improves the adhesion between the wiring pattern and the filler resist. Furthermore, soldering during component mounting has the effect of improving the soldering properties.

[Brief explanation of the drawing]

FIG. 1 is a vertical cross-sectional view of one embodiment of the present invention, and FIG. 2 is a vertical cross-sectional view of a conventional example. 1...Through hole, 2.2'...Wiring pattern, 3
... Copper foil, 4 ... Electroless copper plating layer, 5 ... Electrolytic copper plating layer, 6 ... Electroless copper plating layer, 7 ... Solder resist, 8 ... Insulating substrate, 9 ···pad. Agent Patent Attorney Susumu Uchiharaf;2 ”m

Claims (1)

[Claims] A printed wiring board characterized in that an electroless plating layer is provided as the top layer of a conductor layer of through holes and a wiring pattern.