Analysis of the causes of virtual welding in SMT patch processing

Welding is the most common defect in SMT chip processing. Sometimes after welding, the front and rear steel strips seem to be welded together, but in fact they do not achieve the effect of fusion. The strength of the joint surface is very low. The welding seam must go through various complicated technological processes on the production line, especially the high-temperature furnace zone and the high-pressure tension straightening zone. Therefore, the welded seam of the false welding is likely to cause a broken belt accident on the production line, which has a great impact on the normal operation of the production line.

1. The design of the SMT patch processing pad is defective. The existence of through holes on the pads is a major flaw in the design of printed circuit boards. Unless absolutely necessary, it should not be used. Through holes will cause solder loss and solder shortage. The pad spacing and area also need to be matched by standards, otherwise the design should be corrected as soon as possible.

2. During SMT patch processing, the printed circuit board is oxidized, that is, the soldering board is not bright. If there is oxidation, an eraser can be used to remove the oxide layer and make the bright light reappear. The printed circuit board is damp and can be dried in a drying oven. The printed circuit board is contaminated by oil, sweat, etc. At this time, it should be cleaned with absolute ethanol.

3. During SMT chip processing, for printed circuit boards printed with solder paste, the solder paste is scratched, which reduces the amount of solder paste on the relevant pads and makes the solder insufficient. It should be made up in time. The filling method can consist of glue dispenser or bamboo sticks.

4. SMT patch processing quality is poor, outdated, oxidized and deformed, resulting in virtual welding. This is the most common cause.

The advantages of SMT chip processing: the advantages of high assembly density, small size and light weight, the volume and weight of the chip components are only about 1/10 of the traditional plug-in components. Generally speaking, after adopting surface mount technology, the volume of electronic products is reduced by 40%~60%, and the weight is reduced by 60%~80%. High reliability and strong anti-vibration ability. The defect rate of solder joints is low. Good high frequency characteristics. Reduce electromagnetic and radio frequency interference. It is easy to realize automation and improve production efficiency. The cost is reduced by 30%-50%. Save materials, energy, equipment, manpower, time, etc.