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Temperature and Pad Surface Finish Effects of Sn-1Ag-0.5Cu Solder Joints Strength under High Strain Rate Test Condition
Keywords: High speed shear test, temperature effect, drop performance of SAC105
The ball impact test (BIT) is a package-level test methodology to evaluate solder joint adhesive in a high strain rate test conditions. Comparing with traditional ball shear test, which usually leads to bulk solder fracturing mode and cannot be utilized to evaluate intermetallic compound (IMC) adhesion, BIT with a higher shear speed (>100mm/s) is capable to evaluate both brittle IMC and bulk solder fracturing modes. According to research papers published in recent years, BIT results with proper statistic methods are believed to correlate to board-level drop performance of packages because their strain rates and failure modes are similar. In this study, BIT on 0.3 mm Sn-1Ag-0.5Cu solder balls mounted on Ni/Au (ENIG), OSP (organic solder preservative) and Ni/Pd/Au (ENEPIG) pads are performed both experimentally and numerically. The impact velocity is 300 mm/s which the order of strain rate is close to one on solder joints subjected to JEDEC board-level drop test loads. Temperature effect is also studied under different test temperatures at 25, 50, 75, 100, and 125'C, respectively. Results indicate that as temperature increases the failure location transfers from IMC fracturing to bulk solder mode with more ductile mechanical responses, and solder impact energy was reduced about 25% from 25'C to 125'C. Hence the drop impact reliability shall be decrease with increasing temperature. Numerical modeling of the impact process is performed to indirectly extract the IMC strength under stress-strain behaviors of the solder joint at different temperatures. The experimental results also show that Ni/Pd/Au surface finish at room temperature leads to higher impact energy than Ni/Au or OSP. The board-level drop impact reliability of TFBGA 14 x 14 mm 409L with these surface finishes was also examined at room temperature. The tendency proves that the impact energy from BIT is a relevant qualitative indicator of the drop impact reliability. Board-level drop performance of packages under high temperature can be predicted.
Chin-Li Kao,
Advanced Semiconductor Engineering (ASE), Inc.
Kaohsiung 811, Taiwan
Taiwan ROC

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