Evaluation of solder joint reliability between PWB and CSP by using high TCE ceramic material

A thermal coefficient of expansion (TCE) mismatch between an alumina ceramic ball grid array (BGA) and a printed wiring board (PWB) causes a large stress in solder joints during a thermal cycling test (TCT). Therefore, we have developed a high TCE ceramic material, TCE of 11.5 ppm//spl deg/C, for the total balance of the TCE mismatch among the substrate, PWB, and Si-die. We have confirmed that the solder joint reliability is drastically improved by using this material. However, we found that the lower reliability is reduced in the case of wire bonded chip assembly type with a potting compound. Stress simulation of finite element method (FEM) has shown that stress of second-level interconnection is decreased by increasing the TCE of chip scale package (CSP). We developed another new high TCE ceramic material for the wire bonded chip assembly type CSP. The TCE and the Young's modulus of this material are 13 ppm//spl deg/C and 110 GPa, respectively. By TCT of CSP, we have confirmed that high reliability is achieved by using this 13 ppm//spl deg/C material.