Feasibility study on board assembly of TSSOP components with NiPdAu PPF finish

The feasibility to assemble the NiPdAu pre-plated lead frames was studied with TSSOP components as a carrier. The wetting behavior of TSSOP components from different suppliers has been evaluated. The components have been assembled on a dedicated test board. Several assembly runs were done under different conditions of pre-aging, applied solder volume, component placement force and reflow profiles. Both eutectic SnPb and Pb-free SAC (SnAg4.0Cu0.5) solder were used. Evaluation was done using visual inspection and lead pull testing. A pre-study was done to define the board assembly conditions and to get some basic understanding of the parameters that define the wetting behavior. Results of the study indicate that the larger pitch components always show evidence of good wetting of the leads and the wetting of PPF components was comparable with the SnPb reference components. For the smaller pitch components, the wetting behavior was different for different suppliers and some lead frames showed higher reject rate with Pb-free SAC solder than with eutectic solder. Based on the outcome of the study, a guideline is proposed to evaluate the wetting behavior of PPF lead frames