SMT solder paste is easy to dry and bridge

SMT solder paste is easy to dry and bridge
SMT patch processing is easy to dry
Solder paste is a kind of soldering material produced with the SMT chip processing industry It is a paste solder, which is uniformly mixed with alloy powder and paste flux carrier Many SMT chip processing manufacturers report that solder paste is easy to dry during production Next, we will introduce the causes and solutions of solder paste drying easily
On the one hand, the solder paste is only used in a small area during reflow soldering, which is easier to dry than the solder paste in the solder paste box. At this time, the solder paste does not melt, and the flux cannot cover the solder joint, resulting in poor solder joint. At the same time, a small amount of solder paste is easier to heat transfer, while high temperature actually makes solder paste more difficult to melt. Therefore, we can properly adjust the reflow temperature curve to solve this problem, or welding in nitrogen environment is a good way to solve this problem.

On the other hand, solder paste does not melt because its components contain volatile flux, which is also the reason why solder paste is easy to dry. Among them, the flux with the largest content of solder paste is rosin, which contains a large amount of rosin acid and is easy to lose its activity at high temperatures. In this case, the temperature during welding shall be controlled to ensure that the temperature is about 200 ° C. Neither too high nor too low is appropriate. At the same time, the quality of the thixotropic agent will also cause the solder paste to dry easily. The poor quality of the thixotropic agent will affect the viscosity of the solder paste. The solder paste with high viscosity is easy to dry. In this case, selecting high-quality solder paste can effectively solve the problem of solder paste drying.
In addition, the use environment, humidity, temperature and other external factors of solder paste will affect the drying and non melting of solder paste in the use process, so we should also pay attention to these external factors. I hope these methods can solve your problems.
Reasons and Solutions of Bridging in SMT Processing
1. Solder paste quality problems
The metal content in the solder paste is relatively high, especially after a long time of printing, the metal content tends to increase, resulting in IC pin bridging;
Solder paste has low viscosity and diffuses to PCB pad after preheating;
After preheating, it diffuses to the bonding pad, and the solder paste is poorly decomposed.
Solution: Adjust the solder paste mixture or use good solder paste.
2. Printing machine system problems
The printer has poor repeatability and unexplained alignment (poor alignment of the steel plate, poor alignment of the PCB), which causes the solder paste to be printed outside the pad. This is usually seen in the production of fine QFP;
The size and thickness of the PCB window are not designed correctly, and the tin lead alloy coating in the PCB pad design is uneven, resulting in excessive solder paste.
Solution: Adjust the printer to improve the coating of PCB pads.
3. Installation problems
Excessive solder paste pressure and diffusion flow after solder paste compression are common causes in production. In addition, the placement accuracy is not enough, components will shift, IC pins will deform, etc., which is easy to cause bridging.
4. Preheating problem
The heating speed of the SMT reflow oven is too fast, and there is no time for the solder paste solvent to evaporate