63/37 Solder Cracking

2/28/2017 7:25:15 PM

Guys, We're seeing what looks like an issue where through hole solder joints from our ive solder process are cracking during the cooling phase of the soldering process. This was detected during thermal shock testing, and we have tracked it back to a pre-existing crack. The crack forms at the corner of the joint with the top side pcb pad and progresses into the bulk solder. The process is a dip soldering process using a custom designed nozzle. It has a short bottom side preheat and then a solder dip. Solder is 63/37. Any advice or thoughts will be greatly appreciated. Thanks