Solder joint separation of IC leads is caused by partial melting and displacement of a lead-free solder joint having Pb contamination in process of wave soldering after reflow soldering. An evaluation method of solder joint separation was developed by focusing on the vertical displacement of the joint, which is defined by IC package size and curvature of a printed circuit board (PCB). It has been clarified that the critical displacement causing the solder joint separation is 15 micrometers or less by the model experiment of wave soldering process. Based on the above data, a new in-process measurement tool of PCBs curvature in wave soldering has been developed. The results of practical wave soldering agree well with the model experiment values.
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