Solder Joint Strength Of Lead Free Solders under Multiple Reflow and High Temperature Storage Condition

Solder joining is one of the interconnection methods in microelectronic packaging. The robustness of the solder ball attachment to the packages determines the solder joint strength between solders and the under-bump metallization (UBM). This paper discussed the solder joint shear strength between Sn/4.0/0.5Cu with containing 20-50 ppm phosporus and Sn/3.8Ag/0.7Cu deposited onto selective plating Ni/Au surface finish TBGA packages. Both were reflowed at a peak reflow temperature of 245plusmn5degC with soaking time 70 second above 220degC. Ball shear testing along with failure mode analysis is used as a destructive method to assess solder joint strength and integrity. Both Sn -Ag-Cu (SAC) were studied under multiple reflow (1x, 2x, 3x, 6x) and high temperature storage (HTS) test at 24, 48, 96 hours. All samples were cross- sectioned to study the IMC thickness that leads to solder joint embrittlement. As a result, Sn/3.8Ag/0.7Cu performs better shear strength after HTS test than Sn/4.0/0.5Cu. Similarly, both show the decreasing of shear strength with increasing number of reflow cycles, supported by IMC thickness measurement that there is no significant different in term of growth and consistency.