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The Investigation of Intermetallic Compound Morphology Effect on the Solder Joint Performance

In this investigation, normal and high speed ball shear test were used to evaluate the solder joint performance. Solder residual fracture mode is always being found in normal ball shear for low strain rate. The strength of solder balls are directly associated with their mechanical property in normal ball shear test. High speed ball shear provide a easier way to judge the solder joint performance at high strain rate compare with ball level drop test. Peak force and energy are from force-displacement curve in high speed ball shear that can not be a judgment standard for the overlapping among different failure mode in real test situation. After high speed ball shear, the brittle fracture surface were inspected and examined by focus ion beam (FIB) treatment. Electrolytic nickel/gold (Ni/Au) deposition process has being used widely to provide flat, solderable pad surface finish on area array (BGA or CSP) packages and printed wiring boards (PWB). Recently, a new surface finish - electroless nickel/electroless palladium/immersion gold (ENEPIG) process has been introduced to improve solder joint performance. These two surface finish with Sn3.5Ag and Sn1Ag0.5Cu solder will be estimated. Sn3.5Ag has better performance with Ni/Au surface finish. For ENEPIG surface finish, Sn1Ag0.5Cu shows superior performance under high speed ball shear test.