Finite Element Analysis Of Moisture And Thermal Induced Stress In Flip Chip Packages

Abstract

The process of moisture absorption and subsequent hygroswelling stress development is a cause of concern in the IC packaging industry. Also thermal stresses developed during the lead free reflow process with a high peak temperature (~ 250oC) add to the problem. In Flip Chip packages, the related effects are high shear stresses at the multilayer interfaces and normal stresses in solder balls. This can lead to phenomenon like delamination at the interfaces and UBM opening. In this work we have made an attempt to simulate the moisture absorption process, subsequent hygroswelling stress development, and thermal stress generated during reflow using established FEA techniques. A generic FC package is used as a test vehicle and the analysis is done for two different underfill materials. Also comparison is made with published results for two different test cases.