Excellent reliability of solder ball made of a compliant plastic core

Recently, BGA (Ball Grid Array) and CSP (Chip Scale Package) are employed as area array connection method. For this connection, solder ball is popular to be used. However there exists large CTE (Coefficient of Thermal Expansion) mismatch between the different constituent substrates and the chips. As a result of that, the solder joints are easily broken by thermal strain, and it causes low reliability. Therefore the various ways have been studied in order to relax the thermal stress. We have developed solder ball made of a compliant plastic core. The Young's Modulus of plastic core is much smaller than that of metal, so it is superior in relaxing the thermal stress. The result of temperature cycle tests showed that it had excellent reliability and enabled much greater resistance to micro-cracks in the solder layer than that of conventional solder balls. In addition, it is superior in holding the gap flatly between upper and lower substrates, because the particle diameter of polymer core is very uniform. In this paper we describe electric resistance, reliability in temperature cycle test, failure strength in exposing at various atmospheres, holding the gap flatly, etc, about plastic-cored solder ball.