Predicted stresses in a ball-grid-array (BGA)/column-grid-array (CGA) assembly with a low modulus solder at its ends

A simple, easy-to-use and physically meaningful predictive model is suggested for the assessment of thermal stresses in a ball-grid-array or a column-grid-array with a low modulus solder material at the peripheral portions of the assembly. It is shown that the application of such a design can lead to a considerable relief in the interfacial stresses, even to an extent that inelastic strains in the solder joints could be avoided. If this happens, the fatigue strength of the bond and of the assembly as a whole will be improved dramatically: low-cycle fatigue conditions will be replaced by the elastic fatigue condition, and Palmgren-Minor rule of linear accumulation of damages could be used instead of one of the numerous Coffin-Manson models to assess the lifetime of the material.