How does one minimize solder tearing in lead free joints for SAC solder after wave soldering and does this affect reliability?
Typically solder tears can be observed when using lead-free solder SAC alloy, particularly in wave soldering and with lead contamination present. This has not been considered as a defect as per IPC-610D specifications. Typically this is a cosmetic effect and some studies have been conducted by the industry that solder tearing does not lead to reported reliability failures. The mechanism for this phenomenon is caused by differences in solder solidification, which is affected by the lead from either the PCB or component lead plating. The differences in solder solidification could result in the solder shrinkage that could result in solder tears visibly noticed at the surface. In certain cases, when the board cooled, the contraction may even result in pads lifting from the surface of the laminate. This was reported in certain studies that lead or bismuth contamination of the alloy close to the joint interface can lead to a difference in solidification rates in the joint. Hence to minimize
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