Thermomechanical Analysis of Surface Mounted Leadless and Leaded Chip Carriers

Understanding the reliability attributes of surface mount attachments requires, among other things, insight into the thermomechanical response of solder joints during temperature cycling. In this paper, the finite element method is applied to study solder joint mechanics and determine the stress/strain distributions developed in solder under thermal expansion of the substrate and package assembly. Leadless and leaded plastic molded chip carriers, surface mounted on a glass/epoxy substrate, are modeled a axisymmetric structures, the responses of which are analyzed for a uniform temperature swing. Solder joint designs are rank-ordered for long term reliability on the basis of the maximum strains developed in the solder fillets.