A mold and transfer technique for lead-free fluxless soldering and application to wafer-level low-temperature thin-film packages

This paper demonstrates a technique to pre-mold and transfer lead-free solder balls for MEMS/electronics packaging applications. A reusable bulk micromachined silicon wafer is used to mold a solder paste and remove excess flux prior to transfer to a host wafer that may contain released MEMS. This technique has been used to fabricate low temperature thin film vacuum packages. Long term (>5 months) reliability of these packages at room temperature and pressure is demonstrated through integrated Pirani gauges. Data from preliminary accelerated lifetime testing (thermal cycling and autoclave soaking) is also offered.