Reliability of Solder Joints in Embedded Packages Using Finite Element Methods

Solder joints serve as both mechanical and electrical connections between elements in a package. They are subjected to shear strains generated as a result of the different behaviors of the elements in the package (tension and compression) due to the differences in coefficients of thermal expansion during service conditions. Some of the causes of solder joint failures are due to the following: Vibration: small rapid displacements of parts of the assembly. This is not necessarily an issue with electronic components but larger parts like automobiles. Humidity: the package being exposed to water or ionic species can undergo corrosion if an electrical bias exists resulting in electrical opens or electrical shorts if the corrosion products are electrically conductive. Thermal Aging: this occurs during the lifetime of the solder interconnects, the package can be exposed to high ambient temperature or high dissipated heat during use. The micro-structure of the solder joint becomes more coarse and brittle. Mechanical Shock: the package undergoes shock during a short term exposure to high loads. Thermo-mechanical fatigue: this type of failure arises as a result of the solder joints going through cyclic strains, due to different coefficients of thermal expansion of individual components in the package during service. The most prevalent long-term reliability issues that can cause interconnect failure are thermal aging and thermo-mechanical fatigue. This study aims to evaluate the reliability of solder joints using finite element method, considering solder joint failure due to thermo-mechanical fatigue. Three variations of the BGA (Ball Grid Array) package are evaluated using the finite element analysis. The SAC305 series lead (pb) free alloy of 96.5% tin, 3% silver, and 0.5% copper is employed for this study