Smt soldering circuit board cold welding cause and solution

Cold welding refers to solder joints with incomplete reflow phenomena, such as the occurrence of granular solder joints, irregular solder joint shapes or incomplete melted metal powder.

1.Too low reflow temperature or too short residence time on the liquidus line, resulting in insufficient heat during smt soldering circuit board reflow, metal powder is not completely melted

2. During the cooling phase, strong cooling air, or uneven conveyor belt movement causes the solder joint to be disturbed, showing a rugged shape on the surface of the solder joint, especially at a temperature slightly lower than the melting point, the solder is very soft at that time

3. Surface contamination on and around the pads or pins inhibits flux capability, resulting in no complete reflow. Sometimes unmelted solder powder can be observed on the surface of the solder joint of the smt soldering circuit board. At the same time, insufficient flux capability will also result in the metal oxide not being completely removed, which will lead to incomplete condensation.

4. Solder metal powder is of poor quality, most of which is formed by the inclusion of highly oxidized powder.

Solutions

1. Adjust the reflow temperature curve: set the appropriate reflow temperature and the  liquid line time

2. Pay special attention to the smoothness of transmission

3. Use a slightly higher flux or increase the amount of flux used; the incoming inspection system should be strictly implemented, and the storage environment of components and smt soldering circuit board should be paid attention to.

4. Do not use inferior solder paste, develop a solder paste management system to ensure the quality of solder paste