Analysis on the causes of insufficient glossiness of reflow solder joint

In SMT processing, many customers usually have requirements for the brightness of reflow solder joints. However, in the process of reflow soldering, the brightness of each reflow solder joint can not be guaranteed to meet the requirements. What is the reason for the insufficient gloss of reflow solder joints? Give me a big analysis.

1. Oxidation of tin powder in solder paste will cause insufficient gloss of reflow solder joint after reflow soldering.

2. The flux in the solder paste itself has an additive that can form a matting effect, which will cause insufficient gloss of the reflow solder joint.

3. During reflow soldering, the preheating temperature of reflow soldering is low, and there are residues that are not easy to evaporate on the surface of the solder joint, resulting in insufficient gloss of the reflow solder joint.

4. After reflow soldering, rosin or resin remains on the surface of the solder joint, which is often seen in actual operation. Especially when rosin solder paste is selected, although rosin solder flux and non cleaning flux will make the solder joint slightly bright, the presence of residues will always affect this effect, especially in large solder joints or IC pins; If it can be cleaned after welding, the gloss of the solder joint should be improved.

5. Since there is no standard for the brightness of reflow solder joints, there must be some distance between the goods after soldering the non silver solder paste and the goods after soldering the silver solder paste. This requires that customers should clarify their solder joint needs to the supplier when selecting solder paste.

6. If the solder paste is not completely dissolved due to insufficient reflow temperature, the gloss of reflow solder joint will be insufficient, or if the flux evaporates in advance due to too high reflow temperature, the gloss of reflow solder joint will also be insufficient.

In fact, in addition to the insufficient gloss of reflow solder joints caused by the above six reasons, the solder joints welded with lead solder paste do not have the good gloss of reflow solder joints containing lead solder paste. The gloss of reflow solder joints only makes the appearance of reflow solder joints unsightly and has no impact on the performance of reflow solder joints.