The necessity of reexamining previous life prediction analyses of solder joints in electronic packages

There are several different constitutive relations for describing the creep behavior of solder to predict the fatigue life of a solder joint. The differences among these constitutive relations for fatigue life prediction of electronic packages are unknown because analysts using finite element programs such as ABAQUS or ANSI'S are generally limited to specific built-in material models. The objective of this study is to implement a procedure that allows the use of various creep models in the analysis of electronic packages using ANSYS. Special user routines are developed so the user can incorporate virtually any creep relation and determine the inelastic strain energy density developed in the three-dimensional solid elements. Comparisons are performed for the modified creep routines and the viscoplastic formulation of Anand's model in ANSYS. It is found that the scheme used by ANSYS to determine plastic work density is incorrect and will be remedied in a future release. The implications of this revision to ANSYS are critical because a change in scheme will make comparisons with past studies and analyses difficult. The value of the empirical parameters based on previous analyses, which are widely used in the prediction of package fatigue life, will have to be reexamined.