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Reflow Soldering Defects - Cracked Joint Solder joint cracking, when it occurs, is normally found after some form of environmental testing. In manufacture it can only be caused by flexture of the board after soldering. Areas that should be checked for the possible causes of flexture are in-circuit test, break-out of multi panels, tight reflow or wave solder fixtures and, of course, just poor handling. An interesting and often forgotten cause of open joints is wave solder topside board temperature. Not exactly a cracked joint, but the visual appearance is the same. When the board goes through the wave, topside joints reflow. With even the best systems, boards flex, leaving some joints open. It can also happen during second-side reflow if only some joints become molten.
Obvious joint crack, like in Figure 2, has been caused by flexure of the board assembly. It may also be caused by quality staff probing the joints during inspection after reflow or, in the case of subcontract, at goods receipt at the customer's site. It is surprising just how much force can be developed with an inspection probe. It is well in excess of the 800-1000 grams seen during joint pull off measurement.
Reflow Soldering Defects:
Text and photos courtesy of Bob Willis |
