Pb-free high temperature solders for power device packaging

Reliabilities of joints for power semiconductor devices using a Bi-based high temperature solder has been studied. The Bi-based solder whose melting point is 270 °C were prepared by mixing of the CuAlMn particles and molten Bi to overcome the brittleness of Bi. Then, joined samples using the solder were fabricated and thermal cycling tests were examined. After almost 2000 test cycles of −40/200 °C test, neither intermetallic compounds nor cracks were observed for CTE (Coefficient of Thermal Expansion) matched sample with Cu interface. On the other hand, certain amount of intermetallic compound such as Bi3Ni was found for a sample with Ni interface. In addition, higher reliability of this solder than Sn-Cu solder was obtained after −40/250 °C test. Furthermore, an example power module structure using double high temperature solder layers was proposed.