Effect of SMC Lead Dimensional Variabilities on Lead Compliance and Solder Joint Fatigue Life

Abstract

Lead compliance is a critical parameter in optimal design and interconnection reliability of surface mount leaded components. The cyclic force transmitted to the solder joint in surface mount leaded components is controlled in part by the lead compliance. In this paper a methodology is presented for the computation of lead stiffness and the prediction of fatigue life of the leaded surface mount components. Three-dimensional finite element analyses have been performed to obtain the 12 × 12 stiffness matrices for both the PQFP gullwing and PLCC J leads and solder joints. These stiffnesses are then used in predictive fatigue life equations to estimate the fatigue life. The stiffness matrices and diagonal lead stiffnesses form the basis for identifying more failure resistant packages. Variabilities in lead and package dimensions provided by different vendors, manufacturing to JEDEC standards, are identified and their adverse effects on solder joint fatigue life are studied with the help of finite element parametric analyses. Eighty different finite element analyses are performed to study the effect of change in lead length, height, width and thickness on the lead stiffness and solder joint fatigue life for both the PQFP and PLCC attachments. Finally recommendations are made in order to obtain a better control on component fatigue life.