Effects of Testing Conditions and Multiple Reflows on Cold Bump Pull Test of Pb-free Solder Balls

Ball pull test has emerged to be an attractive alternative to the traditional ball shear testing method for characterizing the attachment strength of solder interconnection. Since this is a relatively new development, so far there is no industrial standard to regulate this testing method. In this study, the pull and shear tests are performed on plastic ball grid array (PBGA) solder balls with Sn-4.0Ag-0.5Cu and Sn-37Pb solders, subject to a wide variety of testing conditions. To investigate the material sensitivity of Sn-Ag-Cu and Sn-Pb solder balls, different pull speeds are used on both kinds of solder balls for comparison. The pull speed ranges from 25 mum/s to 5000 mum/s, while the shear speed ranges from 25 mum/s to 500 mum/s. The pull and shear tests are also conducted on samples with Sn-Ag-Cu and Sn-Pb solder balls after multiple reflows. Various failure modes of ball shear and ball pull tests are discussed for comparison. The sensitivity of both methods on brittle interface fracture is addressed. Furthermore, different pull speeds are applied to Pb-free solder samples after multi-reflows. Favorable testing conditions will be recommended