JPS5916438B2 - Screen printing method for printed circuit board - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to screen printing of printed circuit boards, and more particularly to screen printing having a non-printing shape in consideration of printing characteristics according to the shape of a circuit pattern.

As circuit patterns on printed circuit boards become denser, it is essential to apply solder resist to printed circuit boards to prevent rust on the circuit patterns or to prevent bridging during soldering.

The method for applying this solder resist is shown in Figures 1 to 4.
There is a commonly used screen printing method as shown in the figure. In screen printing, a pattern is formed on a screen 2 made of stainless steel, polyester, etc. according to the shape of the circuit pattern so that the solder resist 9 is not coated, and then a suitable pattern is formed to match the circuit pattern 6 of the printed circuit board. This is a method in which the solder resist 9 is applied onto the printed circuit board by leaving a space between them and extruding the solder resist 9 onto the printed circuit board using a squeegee from above the screen 2. At this time, depending on the material such as stainless steel or polyester, and the printing conditions such as the angle, pressure, and speed of the squeegee, the solder resist 9 may be applied to areas of the circuit pattern 6 and signal lines 8 of the printed circuit board that should not be applied. It has been applied (solder resist)
(This is called a failure of the solder resist 9), or conversely, the solder resist 9 may not be applied to the areas where it should be applied (
A defect called "insufficient solder resist coating defect" occurred, which required rework each time. This is because when extruding the solder resist from the screen onto the printed circuit board, the squeegee is moved along the printing direction while applying pressure from above, so the screen is pulled along the printing direction and the printing pattern This is due to stretching in the printing direction. These expansions and contractions are unavoidable in screen printing, and as a countermeasure, the non-printed shapes were made evenly larger than the circuit patterns. However, in the case of a high-density pattern, this method is not suitable because the spacing between pads and lines is small, so there is a possibility that defects due to insufficient resist coating may occur.
SUMMARY OF THE INVENTION An object of the present invention is to provide a screen printing method that does not cause defects such as resist coverage or insufficient resist coating, regardless of the screen material, printing conditions, etc.

υ In order to achieve the above object, the present invention allows the printing pattern formed on the screen to have a margin in the direction of expansion and contraction, so that even if there is expansion and contraction during printing, resist overlay and resist coating insufficient defects will not occur. The reason is that solder resist is applied to predetermined locations.

Next, an example of the present invention will be explained using □. Figure 1 shows “
A typical screen version is shown. FIG. 2 is a partially enlarged view of a printing pattern of a conventional screen plate, and FIG. 3 is an example of a partially enlarged view of a print pattern of a screen plate according to the present invention. FIG. 4 shows the state of solder resist application on the printed circuit board when the solder resist is applied using a screen having the printed pattern shown in FIG.
FIG. 5 shows the solder resist coating state on the printed circuit board when the solder resist coating is performed using a screen having the printed pattern shown in FIG. 3. FIG. FIG. 6 shows an embodiment of the invention in the case of a round pad. Screen printing is a method in which pressure is applied to a squeegee to push out the ink, and the coating is applied by leaving an appropriate gap between the printed circuit board and the screen, so the elongation in the printing direction is large. When printing with the screen 2 shown in FIG. 2, since the distance between the pad 6 and the solder resist 9 is uniform, resist overlapping in the printing direction is likely to occur.

Also, if the non-printing shape 4 is uniformly enlarged, the signal line 8
This means that solder resist will not be applied to the area. In order to eliminate these defects, taking into account elongation during printing and noting that the printing direction is generally along the signal line 8, we created a non-printing shape 5 as shown in Figure 3. By increasing the elongation in the printing direction where the elongation during printing is greater, the resist cover D can be eliminated and at the same time, resist coating will not be insufficient.
Further, even in the case of the round pad 10, as with the square pad 6, the problem can be solved by enlarging the non-printing shape in the printing direction.
In this case, the non-printing shape may be the rectangle 5 shown in Figure 3, but since the non-printing shapes of the printed circuit board and the screen are matched visually, the non-printing shape is oval as shown in Figure 6. If the shape is printed, alignment can be done efficiently.
As explained above, according to the present invention, it is possible to greatly reduce solder resist cover D and insufficient solder resist coating in the solder resist coating process for high-density printed circuit boards.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing a general screen plate, Fig. 2 is a partially enlarged view of a conventional printed pattern, Fig. 3 is a partially enlarged view of a printed pattern according to the present invention, and Fig. 4 is a conventional printed pattern. Figure 5 is a diagram showing an example of the surface condition of a printed circuit board when a solder resist is applied with a printed pattern according to the present invention; FIG. 3 is a diagram showing another embodiment. 1...Screen frame, 2...Screen, 3...Print pattern, 4...Non-print shape, 5...Non-print shape , 6... Padded, 7... Through hole, 8... Signal line, 9... Solder resist, 10...
...Patsuto.

Claims (1)

[Claims] 1. In a screen printing method for printing solder resist on a printed circuit board using a screen on which a printing pattern consisting of a non-printing part (non-printing shape) and a printing part is formed, the non-printing shape is A screen printing method for a printed circuit board characterized by allowing a margin in the direction in which the printed pattern expands and contracts.