Finite element analysis of Sn-Ag-Cu solder joint failure under impact test

BGAs packaging offer high pin counts and lower interconnecting space, and are suitable for high density packaging. However, it is difficult to inspect individual solder joints on BGA assembly by conventional visual methods and need a complicated practice on rework. Ball impact test is a useful method to estimate the reliability of BGA solder joint. In this study, the three-dimensional explicit finite element analysis is employed to carry out dynamic responses of solder joints under ball impact test. Through a three-dimensional explicit element analysis incorporated with contact, fracturing and fragmentation mechanisms, transient fracturing of the solder joint subjected to high speed impact test is investigated. Different IMC strengths are specified and corresponding structural responses and failure modes are examined in this paper. The impact force histories with respect to different IMC strengths are clearly show by the method of finite element simulation. From the results, three kinds of failure modes can be found which tally with the actual failure modes of ball impact test. The IMC strength plays an important role in determining the failure mode in ball impact test. Model (totally brittle break in IMC layer) occurs when the IMC strength is relatively low (below 300 MPa) with very short impact duration (within 30 mus); Model 2 (interfacial break with some solder remaining on the fracture surface) occurs when the IMC strengths are between 400 MPa and 700 Mpa, the impact duration increase to 40~100 mus; and when IMC strength exceeds 700 MPa; Model 3 (totally ductile break in solder bulk) happens with impact duration above 100 mus. The impact curves of Model 1 and Model 2 are similar to half-sine profile while Mode 3 is followed by a prolonged vibration pattern due to interaction between the shear tool and solder.