JPH04152692A - Manufacture of printed wiring board - Google Patents

Abstract

PURPOSE:To enable a wiring pattern of high density to be insulated without deteriorating it in reliability of electric connection by a method wherein 6 screen printing stencil used for the insulation of the side of a wiring board is made to print solder resist ink on the whole-surface, and another screen printing stencil for the another side of the board is made to cover only the part around lands which electrically connect components. CONSTITUTION:The insulation of a wiring board is executed through a screen printed method, a screen printing stencil used for the insulation of the side of a wiring board is made to print solder resist ink on the whole surface, and printing conditions are so controlled as to apply resist ink onto the corners of through-holes or viaholes and a part of the inner wall of them. Another screen printing stencil for the another side of the board is made to cover only the part around lands which electrically connect components. By this setup, a land 1 is accurately exposed on the side of a wiring board where a soldering operation is carried out, and all the other side of the board where components are mounted is insulated, whereby a printed wiring board can be enhanced in connection reliability.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a method for manufacturing a printed wiring board, and particularly to a final step of insulating the board.

(Prior art) Conventionally, in order to insulate printed wiring boards, areas other than those where electronic components are soldered are selectively covered with solder resist ink using screen printing, and then the solder resist ink is exposed to heat or ultraviolet rays. A method of hardening was used.

By the way, in recent years, with the development of electronic devices, printed wiring boards have become more densely arranged, and the spacing between the lands and signal lines for connection with electronic components has become smaller. It is becoming difficult to selectively expose solder resist.

As a solution to this problem, a solder resist using an ultraviolet-sensitive resin film was developed to expose only the land portion, as shown in Figure 2, and a photoprinting method was used to create a solder resist with higher precision. A method of forming a solder resist has been proposed, and as shown in FIG. 3, a method has been proposed in which the corners of the through hole and part of the inner wall thereof are covered with a solder resist.

(Problems to be Solved by the Invention) In such conventional methods, forming a solder resist using the photoprinting method has high accuracy, but when developed, a part of the film dissolves inside the through hole. When a thin insulating film is formed and flow soldering is performed, an electrical connection may not be possible, or the film residue may decompose due to heat and the resulting gas may generate bubbles called blowholes, both of which impair the reliability of electrical connections. It may cause damage. In addition, the method of covering the corners and part of the inner wall of the through hole with solder resist ink, especially when flow soldering is used, prevents the solder from penetrating into the through hole, which also creates a blow hole and makes the electrical connection reliable. It may damage your sexuality.

An object of the present invention is to provide a method for manufacturing a printed wiring board that can insulate a high-density wiring pattern without impairing the reliability of electrical connections.

(Means for Solving the Problems) The method for manufacturing a printed wiring board of the present invention includes a method for manufacturing a printed wiring board having two or more layers of conductor circuits and a through hole or a by-hole in the final insulation step of manufacturing the printed wiring board. Insulation is performed by screen printing method, and the screen printing plate for insulating one side of the wiring board is capable of printing solder resist ink on the entire surface, and the corners of through holes or via holes and their inner walls are The printing conditions are controlled so that the resist ink is applied to a part of the board, and the screen printing plate for insulating the other side of the wiring board is used to cover only the area around the lands that electrically connect the parts. Assume that the number of printing is 5~
It is characterized in that the printing is performed within a range of 100 times, and the other screen printing plate is corrected in consideration of shrinkage within the range of the number of times of printing.

The printing conditions here include the material and viscosity of the solder resist ink, the mounting angle of the screen printing squeegee, the hardness of the squeegee, the tension of the screen printing plate, the mesh of the plate, and the Printing pressure refers to the printing speed, number of printing times, etc.

What you need to be especially careful about is the elongation of the plate depending on the number of printings.The plate elongates for the first few shots after printing starts, and then remains stable until about 150 shots, but beyond that it will elongate. When this happens, the plate material becomes fatigued and begins to stretch again. Therefore, the first few shots are not suitable for production, and once the number of printings exceeds 150, it is necessary to replace the plate.

(Function) By the method of the present invention, as shown in Fig. 1, only the land portion of the surface to be soldered is always exposed with high accuracy, and the opposite component surface is entirely insulated, which improves the reliability of the connection. By controlling the plate management and printing conditions, you can work within the range where the plate is stable and ensure printing accuracy.

Example 1 An epoxy resin-based ink was used as a solder resist ink to insulate a three-layer printed wiring board. A high-density wiring board with a line width of 0.15 m5 and a minimum line-to-land spacing of 0.2 mm was used for this wiring board. The required accuracy was obtained by printing 5 to 150 times, and no blowholes were generated during flow soldering. The reliability of the connection was also good, and there was no decrease in connection resistance even after floating in a solder bath for 10 seconds or more.

(Effects of the Invention) As explained above, the present invention makes it possible to provide a manufacturing method that efficiently insulates a high-density wiring board while ensuring connection reliability.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing one embodiment of the present invention, and FIGS. 2 and 3 are sectional views showing a conventional example. Explanation of symbols■. Land part of through hole 2゜Insulating layer factor diagram

Claims (1)

[Claims] 1. In the final insulation process of manufacturing a printed wiring board with two or more layers of conductor circuits and through-holes or by-holes, the wiring board is insulated by screen printing, and one side of the wiring board is insulated. A screen printing plate for insulation can be printed with solder resist ink on the entire surface, and the printing conditions are controlled so that the resist ink is applied to the corners of the through hole or via hole and a part of the inner wall thereof, A screen printing plate for insulating the other side of the wiring board was made to cover only the periphery of the land that electrically connects the parts, and the number of printing was performed in the range of 5 to 100 times, and the above-mentioned A method for manufacturing a printed wiring board, characterized in that the other screen printing plate is corrected in consideration of shrinkage within the range of the number of printings.