An idealized shape of CuCGA solder joint and its load-carrying advantage

Solder joint geometry feature is important for packaging miniaturization design. To improve the thermo-mechanical reliability of lead-free packaging, a copper column interconnect with idealized solder joint shape, composed of a double-funnel shaped copper column and two lead-free solder fillets at both ends of the column, was designed to replace the high-Pb solder column interconnect in ceramic column grid array (CCGA) and the conventional copper column interconnect in ceramic copper column grid array (CuCGA) package. Mechanical behaviors under shear loading and bend loading were studied using finite element method (FEM). Results indicate that the peak plastic strain in the designed CuCGA interconnect decreases slightly compared with the conventional CuCGA interconnect, however the peak plastic strain in its solder fillets decreases significantly due to stress concentration locations transfer from the interface of solder and copper column to the inside of funnel-shaped copper column. Therefore the lower strength solder fillets were protected, a higher load-carrying ability for the CuCGA package could be expected.