Analysis of stress buffer effect of polyimide for board level drop test by a finite element analysis

Portable electronic products has been extended for high-performance and high-density LSI applications in recent years. One of the major concerns of portable electronic products is performance of package during drop impact because fracture and/or delamination of the fine joint parts are concerned. In this report, buffer function of polyimide layer by drop test is discussed. Our focused structure is Wafer Level CSP (WLCSP) without UF. The drop impact of microelectronics packages was calculated with a finite element analysis (FEA) using a zooming technique. This study is focused on Polyimide (PI) layer such as the effect of shape factors (thickness, opening diameter) and mechanical properties (modulus, strength, poisson's ratio). Finally, it was found that the factors of PI thickness and PI modulus especially have significant contributions to stress responses. The results indicate thick PI thickness and high modulus PI is recommendable to apply various different structure designs.