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 diff erences among these constitutive relations for fatigue life prediction of e lectronic packages are unknown because analysts using finite element progra ms such as ABAQUS or ANSI'S are generally limited to specific built-in mate rial models. The objective of this study is to implement a procedure that a llows the use of various creep models in the analysis of electronic package s using ANSYS, Special user routines are developed so the user can incorpor ate 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 det ermine plastic work density is incorrect and will be remedied in a future r elease, The implications of this revision to ANSYS are critical because a c hange in scheme will make comparisons with past studies and analyses diffic ult. The value of the empirical parameters based on previous analyses, whic h are widely used in the prediction of package fatigue life, will have to b e reexamined.