JPS6072294A - Method of forming solder resist - 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 (1) Technical Field of the Invention The present invention relates to a solder resist that covers a conductor pattern on the surface of a printed circuit board, and more particularly to a method for forming a solder resist that covers a dense conductor pattern.

(2) Background of the technology By applying a heat-resistant coating of synthetic resin paint such as epoxy to the conductor pattern on the soldering surface of a printed circuit board by screen printing, etc., a solder resist coating is formed.
When soldering a printed circuit board by dipping it into molten solder,
A method to prevent bridges between conductor patterns due to molten solder is essential as a pretreatment for soldering with depths as the pattern density of conductor patterns becomes denser. As a result, uniformly coating the surface and side surfaces of a conductor pattern with a desired thickness is
This is difficult because the viscosity of the solder resist paint is relatively high, and in areas where the coating is thin and fragile, solder balls and bridges between conductive patterns may occur due to melting of the solder plating layer on the surface of the conductive pattern. It is desired to form a solder resist film reliably even on dense conductor patterns.

(3) Prior art and problems Figure 1 is a sectional view of the surface of a conventional solder resist printed circuit board. In the figure, 1 is the base material of the printed circuit board, 2 is a land, 3 is a through pole, and 4 5 is a conductor pattern, 5 is a gap between land 2 and conductor pattern 4, 6 is a gap between conductor patterns 4, 7 is a copper layer, 8 is a solder layer, 9
indicate solder resist coatings, respectively.

As shown in FIG. 1, when the reference grid between the through poles 3 provided on the surface layer of the printed circuit board is 100 mils, the relatively dense conductor pattern has a width of 14 mm.
00μrfl, the width of the conductor pattern 4 is 140μm, the gap 5 between the land 2 and the conductor pattern 4 and the conductor pattern 4
The gaps 6 between the lands 2 are each 180 μm, and three conductor patterns are provided between the lands 2.

The land 2 and the conductive pattern 4 are composed of a 30 μm thick copper layer 7 on the base material 1 and a 30 μm thick solder layer plated on the copper layer 7.

Generally, the surface of the land 2 on the surface layer of a printed circuit board is a soldering area, and the conductor pattern 4 is a non-soldering area.
The viscosity is adjusted to about centiboise and printed using a silk screen or the like to form the solder resist film 9. However, when the printed circuit board is brought into contact with the molten solder for soldering, the temperature of the molten solder is approximately 260°C. In order for the solder resist 9 coating to not be destroyed during a contact time of about 10 seconds, the solder resist 9 coating needs to have a thickness of at least 20 μm or more.

To obtain this thickness, it is necessary to increase the viscosity of the synthetic resin paint that forms the solder resist 9, but the solder resist 9 that covers the non-solder areas is screen printed using such a high viscosity synthetic resin paint. When printed by pressing with etc., the synthetic resin paint covers the surface of the conductor pattern 4, but
Gap 5.6 has a gap interval of 180 μm and a gap depth of 60 μm, so the synthetic resin paint does not fill the gap 5.6 and is partially empty F! A, the land 2 and the conductor pattern 4 and the respective side surfaces between the conductor pattern 4 and the synthetic resin paint did not come into contact with each other, and the film thickness of the solder resist 9 did not reach the desired 20 μm in these areas, and the printing When a circuit board is brought into contact with molten solder for soldering, the solder layer 8 on the copper layer 7 melts, creating a high pressure within the hermetic covering of the solder resist 9 that covers the solder layer 8, causing the solder resist to melt. The molten solder of the solder layer 8 may eject from the weak part where the thickness of the coating 9 does not reach 20 μm, forming a so-called solder ball, and flow out into the voids of the gaps 5 and 6, bridging the gaps. be.

(4) Purpose of the Invention In view of the above-mentioned conventional drawbacks, the present invention provides a method for forming a solder resist film on the surface layer of a printed circuit board consisting of a dense pattern, in which the thickness of the solder resist film exceeds a desired value. It is an object of the present invention to provide a method for forming a solder resist that can ensure high quality.

(5) Structure and object of the invention According to the present invention, the gap in the non-soldering area is filled with synthetic resin paint in advance and the surfaces are leveled, and then the synthetic resin paint is further applied. This is achieved by providing a method for forming a solder resist.

(6) Examples of the invention Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 2 shows a cross-sectional view of a printed circuit board for explaining the method of forming a solder resist according to the present invention, and in the figure, 10 indicates synthetic paint filling the gaps 5 and 6.

As shown in FIG. 2, the method for forming a solder resist according to the present invention is to form a film of solder resist 9 on the land 2 and conductor pattern 4 on the surface of a printed circuit board. Using a silk screen mask (not particularly shown) corresponding to the gaps 6 between the conductor patterns 4, a low viscosity epoxy synthetic resin of about 200 centipoise is pressed with a squeegee, and the gaps 5 in the non-soldering areas are closed. and after filling all gaps 6,
The surface of the filled synthetic paint 10 is leveled so that it is flush with the surfaces of the land 2 and the conductor pattern 4, and after the filled synthetic paint 10 is cured, the non-soldering area is again made into 400 cm voids using a silk screen or the like. By squeegeeing a relatively high viscosity epoxy synthetic paint to form a film of solder resist 9 closely on the surfaced non-soldering area, the sides of the land 2, the side of the conductor pattern 4, and the conductor are formed. All surfaces of the pattern 4 are reliably coated with a coating of epoxy-based synthetic paint of a desired thickness or more.

(7) Effects of the Invention As explained in detail above, according to the solder resist method of the present invention, gaps in the non-semi-region are filled in advance with a low-viscosity synthetic paint such as epoxy. After the surface is hardened, the non-solder area is covered with a solder resist film, so the gap in the non-solder area is reliably covered without any voids, and the solder resist is applied to the surface of the surface of the patterned gap and the paint on the surface of the conductor pattern. The resist coating was easily formed, and the coating of the solder balls 1 to 1 in the soldering area was perfect, and the occurrence of bridging between the solder balls and the opposing conductor side walls could be reliably prevented.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of the surface of a conventional printed circuit board coated with a solder resist, and FIG. 2 is a cross-sectional view of the printed circuit board for explaining the method of forming a solder resist according to the present invention. In the figure, 2 indicates a land, 4 a conductor pattern, 5 a gap between the land 2 and the conductor pattern 4, and 9 a solder resist film. Chapter l Companion 2121

Claims (1)

[Claims] To form a solder resist film on the surface of a printed circuit board, the gas-filled areas between the conductor patterns are filled with a low-viscosity solder resist paint, hardened and leveled, and then solder resist paint is printed on the leveled surface. A method for forming a solder resist, characterized by: