SOLDER JOINT SEPARATION or failure can happen for a variety of reasons, even when every aspect of the assembly process is working correctly. In FIGURE 1 the connector pin has separated from the surface of the printed board after reflow. The solder paste has reflowed correctly, and there is evidence on the pad of the joint and how the solder had successfully wetted up and around the contact to form a continuous fillet before the pin detached. There are some small voids in the joint, but these are very common between flush-mounted surfaces.
[FIGURE 1 OMITTED]
If faced with this type of defect, take time to look at both surfaces--the PCB and connector pin--to understand and investigate the failure. In this case, there was plating separation from the connector pins. The solder paste reflow process was satisfactory, and solder wetted the plating and formed what looked like a perfect solder joint that would have passed any inspection or AOI. The plating adhesion to the base material was the problem, and just like pulling your foot out of a shoe, you are left with a perfect mold of the pin, but not a strong or reliable joint.
Conducting reflow simulations on the connector pins showed evidence of outgassing from the plating and complete dewetting on the...