High Temperature Hardness of Lead-free and Composite Solders

Solder joints in microelectronic devices are frequently operated at an elevated temperature in service. They also experience plastic deformation caused by temperature excursion and difference in thermal expansion coefficients. Deformed solders can go through a recovery and recrystallization process at an elevated temperature, which would alter their microstructure and mechanical properties. In this study, to predict the changes in mechanical properties of Pb-free solder joints at high temperatures, the high temperature microhardness of several Pb-free and composite solders was measured as a function of temperature, deformation, and annealing condition. Solder alloys investigated include pure Sn, Sn-0.7Cu, Sn-3.5Ag, Sn-3.8Ag-0.7Cu, Sn-2.8Ag-7.0Cu (composite), and Sn-2.7Ag-4.9Cu-2.9Ni (composite). Numbers are all in wt.% unless specified otherwise. Solder pellets were cast at two cooling rates (0.4 and 7 oC/s). The pellets were compressively deformed by 30 % and 50 % and annealed at 150 oC for 2 days. The microhardness was measured as a function of indentation temperature from 25 to 130 oC. Their microstructure was also evaluated to correlate with the changes in microhardness.

By: Joo Won Lee; Zin H. Lee; Sung K. Kang; Da-Yuan Shih; Hyuck Mo Lee

Published in: RC23578 in 2005


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