Nowadays, the use of lead-free solder paste in SMTproduction line processing plant has become the mainstream solder paste. When using lead-free solder paste, it is easy to appear that the solder joint is not bright enough, which does not meet the requirements of the customer for brightness. How can the solder paste brightness be improved?
I. Choose the solder paste with good oxidation resistance and high silver content
Lead-free solder paste placed in the air, easy to volatile oxidation, reduce the performance of the solder paste, then the brightness of the solder paste solder joint is not so good, so we should choose good oxidation resistance solder paste, while avoiding the use of lead-free solder paste placed in the air for more than 24 hours. Choose lead-free solder paste with high silver content, and can increase the brightness of lead-free solder paste solder joint, but increase the silver content, the cost will rise.
II. Improve reflow oven welding process
First, adding nitrogen during reflow increases the brightness of the solder joint of the lead-free solder paste. There is another reason why the brightness of the solder joint is not enough, that is, the residual flux. At this time, the temperature curve of reflow soldering can be adjusted, and the time of the constant temperature zone of reflow soldering can be appropriately increased, so that the flux can volatilize to a greater extent, which can help to brighten the solder joint.
III. Correct selection of flux
Sometimes the solder joint will remain yellow material, this is due to the residual flux, so in order to improve the brightness of the solder joint, but also the correct selection of flux, the choice of cleaning flux will be of certain help to the brightness of the solder joint.
If you want to use lead-free solder paste, the solder joint is brighter, a very effective way is to increase the content of silver, but the cost will naturally increase, which often makes many people prohibitive. Therefore, the more effective method is to improve the reflow welding process, choose good solder paste and flux.