Effect of solder pad opening size and various pad metallization substrates on Sn-Ag-Cu solder joint under high speed shear test

The purpose of this study is to investigate the mechanical behavior of Sn-Ag-Cu solder joint under high speed shear test. A impact testing method with shear rate up to 1.0 m/s was set up to measure the solder joint reliability. The effects of differential substrate pad opening and pad metallization were also considered. The study focuses on failure mode analysis and examines characterizing strengths of Sn-Ag-Cu lead-free solder joint at shear rates of 0.3 m/s and 1.0 m/s. Four types of failure mode were observed from the failure section of the solder joint. In Mode M1, fractures occurred at the interface but not remain the solder on the pad. In Mode M2, fractures occurred at the interface with some solder residue remaining on the pad. In Mode M3, fractures occurred at the bulk solder. In Mode M4, fractures on the substrate lifted. The present results were shown that the percentage of M2 mode failure goes up as pad opening increases for two types of substrate. The M1 failure rate of OSP pad metallization substrate is greatly increased due to decrease in pad opening. The M3 and M4 failures are not found at 1.0 m/s impact speed. Overall comparison of peak load and energy-to-peak load performance revealed that the Sn-Ag-Cu bonds to the OSP pad finish were more tough than that of the Ni/Au pad finish for all shear test condition. The interfacial strength reduces with a decrease in pad opening both the Ni/Au and OSP pad finish substrate. In the case of OSP, shear strength and toughness are significantly dependent on solder pad opening size.