Flip chip assembly on PCB substrates with coined solder bumps

The objective of this work is to investigate the flip chip assembly on PCB substrates with coined eutectic solder bumps. In this study, stencil printed 37Pb/Sn solder flip chip bumping and subsequent coining processes were performed on both electroless Ni/Au and OSP (Organic Solderabilty Preservatives) finished PCBs, and then electroplated 97Pb/Sn flip chip bumped chips were successfully assembled. The structure, assembly processes, and reliability data of this package made of high melting temperature 97Pb/Sn flip chip bumps and etectic 37Pb/Sn PCB bumps interconnection were investigated. Reliability tests, using thermal cycling (-55 to 125 degreesC), PCT (Pressure Cooker Test), 85/85 (85 degreesC and 85 % humidity), and mechanical testing (die shear test) were performed. And daisy chain resistances were also measured to characterize the interconnections and to monitor degradation effects. Cross-section analysis was performed after reliability tests to inspect flip chip solder joints with respect to phase transformation and growing of intermetallic compounds (IMCs) at the solder/PCB interfaces. From the experimental results, it was found that the combined bumps structure of 97Pb/Sn at chip and 37Pb/Sn at PCB was very reliable, and OSP finish was as good as Ni/Au finished PCB for these applicatons.