STUDY OF THE EFFECT OF HUMIDITY ON THERMAL CYCLING OF A BALL GRID ARRAY (BGA) PACKAGE

Abstract

Thermal Cycling (TC) Test is one of the most important reliability tests in the packaging and semiconductor industry. Humidity on the other hand is one of the significant factors for the reliability of packages, since there are several failures due to moisture absorption in packages. Humidity in packages can lead to soften them and decrease adhesive strength resulting into delamination near the solder tip and wire bond joint, which results in poor electric performance as well as reduced mechanical reliability. In addition, decrease in adhesive strength also causes corrosion in that area which leads to package failure. Absorption of humidity causes oxidization on the solder and well as the PCB board which have been studied in the paper. To analyze this effect of humidity, we followed the JEDEC standards. To induce humidity in the material, the solder and PCB samples were kept in an environmental chamber for 5 days or 120 hours. The material properties of these samples were measured and analyzed. These samples are then examined under SEM and EBSD to analyze the micro structural changes and material spectroscopy. This paper deals with the study of the effect of humidity on thermal cycling of BGA packages through simulation and experimental verification. The temperature range of the thermal cycling test on the package is -40˚C to 125˚C. For Finite Element Modelling commercial software ANSYS and ANSYS Fluent are used. Also, a humidity modelling technique is proposed which is validated by experimental data. Also, a detailed comparison is made on deformation, stresses and strains in normal thermal cycling against thermal cycling with humidity. In this study, Multiphysics simulations and reliability analysis has been done to analyze failures in the package.