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PCB Tech
How to improve the PCB production process
PCB Tech
How to improve the PCB production process

How to improve the PCB production process

2021-10-25
View:186
Author:Downs

In today's fierce competition in the PCB market, production technology is one of the main ways to create fast delivery, reduce costs, and improve quality. Here are two issues that often appear in the PCB production process, but many manufacturers do not know how to improve.

1. In the process of PCB production, the surface of the photosensitive solder mask black and white oil often appears after development. There is a layer of black and white dust on the surface, which can be wiped off with dust-free paper.

Similar problems have occurred in ten circuit board factories, and everyone who called for advice said that it was baked to death during pre-bake, which caused unclean development. They generally used to shorten the baking time. Way to solve this problem, but the result was counterproductive. When asked about their baking conditions, most of them are at 75 degree Celsius*25-35 minutes, and double-sided simultaneous printing.

As a PCB factory welding room supervisor, you should be able to solve this problem by yourself, and the simplest problem is often worsened by unskilled people. I have seen a PCB factory welding room supervisor order the griller to use it after such a problem The photosensitive white oil board was baked at 75 degree Celsius*20 minutes, and the exposure ruler achieved 8 levels of residue. As a result, the whole board was a white fog after the development. The supervisor was confused about the reason and brought great losses to the company.

The above problem is actually very simple. The main reason is that the photosensitive black and white oil baking time is insufficient, and the exposure energy is too low, causing the photosensitive black and white oil bottom layer to not fully achieve the effect of heat and light dual curing, so the surface layer will fall off after development The black and white oil is in powder form, which will appear on the surface after being dried by the developing machine, which can be wiped off with dust-free paper.

To solve this problem, we only need to pre-bake for a long time. Generally, the condition of pre-bake photosensitive black and white oil is 75 degree Celsius+5 degree Celsius*40-50 minutes, depending on the thickness of the board. Use 21-frame exposure to achieve 11-level residual and 12-level clean.

If you encounter similar problems, please refer to the above process, I believe it will achieve the desired effect.

2. When printing solder mask oil, it is often found that there is oil and development in the socket.

Similar problems have been encountered by several PCB factories. The main reason is that there is oil in the hole after development and the hole is not clean. When the hole is used for backwashing, it is still not clean. Finally, the caustic soda is used for backwashing, but the result is still the oil in the hole. It still can't be washed off, and the residual oil in the hole can't be disposed of in the end, resulting in waste.

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If such a problem is correctly handled, it will not cause abandonment. The main reason for the abandonment is that the silk screen is not well controlled during printing, which makes the oil into the hole too serious, and some plug the hole too badly. During pre-baking, the oil in the hole is too thick, can't the oil in the hole be completely re-developed? We can do a test and use a small blade to pick out the oil in the hole. It is certain that the oil in the hole is thin. If the thin oil is re-developed, the oleoresin bond on the wall of the hole cannot be washed away.

Why can't I wash it off again with caustic soda? In the case that the ink itself is not pre-baked, the ink is soaked in Na2CO3 and soaked in caustic soda, so that the wet ink is killed by the attack of two chemical solutions, and the color of the ink is immersed in the base material of the hole wall. It is the same as the common ink in our lives that it is soaked in yarn and cannot be washed off. As a result, there is a layer of green oil in the hole at the end, causing waste.

Having said so many problems, I have also done many experiments to solve this problem. Once I found that a QC officer in a company’s QC department detected that there was oil in the hole of a 100PNL board that could not be washed away, so I took the 100PNL board and used it. Return to 75°C for 10 minutes, and then develop. The result is that 100% of the plates are fully developed. Then take the oily plate in the 20PNL hole without returning and develop directly. As a result, 70% of the plates are still not clean. The above proves that the oil in the hole If it is not completely pre-baked, the re-imaging is wrong. high-speed download

The printer should be controlled to prevent the ink from entering the hole too seriously. If there is oil in the hole after development, you can re-bake and re-develop. Do not continue to develop, or use caustic soda to re-foam directly to avoid waste.