SOLDER HIERARCHY FOR LEAD FREE SOLDER JOINT

摘要

A lead free solder hierarchy for use in the second level solder connection of electronic components such as joining an electronic module (20) to a circuit board (120). An off-eutectic solder (60) concentration of SnCu or SnAg is used for the module side connection. This off-eutectic solder (60) contains sufficient intermetallics to provide the module side connection with a robust second level assembly and rework process. The off-eutectic composition (60) provides an inter­metallic phase structure in the module side fillet during assembly. The inter­metallic phase structure eliminates problems of tilt and collapse during second level assembly and aids in rework by providing a more cohesive joint allowing removal of the columns (100) from the board (120) without simultaneous removal from the module (20).