A Novel High-Temperature Pb-Free Solder Paste with Enhanced Performance for Power Discrete Packaging Applications

Abstract

Durafuse™ HT—a novel high-temperature lead-free (HTLF) solder paste design, combining two constituent powders has been developed as a drop-in solution to replace the high-Pb solder pastes in power discrete applications. In the design, the rigid high-temperature SnSb-based powder maintains the high-temperature mechanical performance and the ductile Sn-rich powder lower the reflow temperature to be comparable to the high-Pb. HTLF-1, one of the HTLF solder pastes with relatively lower Sn-rich phase, maintained bond shear strength up to 15MPa, even around 295°C. Another solder paste, HTLF-2, having relatively-higher Sn-rich phase, had the comparable bond shear strength to Pb92.5/Sn5/Ag2.5, around 295°C, but exceeded substantially below 250°C. The encapsulated discrete components were successfully built with both HTLF solder pastes using the existing high-Pb process, which includes the paste deposit, die & clip placement, residue cleaning, molding & curing etc. It demonstrated the drop-in processing compatibility. Those components had successfully gone through the traditional product qualification tests, namely the pre-conditioning, the moisture sensitivity level 1 (MSL-1) and 1000 cycles of TCT (−55/175°C). Both HTLF solder pastes had the superior RDS(on) comparing to Pb92.5/Sn5/Ag2.5 before and after 1,000 cycles TCT (−55/175°C). The intrinsic lower electrical resistivity of Sn was attributed to superior electrical performance.