Effect of Design Factors of a Mobile Phone on the Reliability Risks of On-Board Packages Under Product-Level Drop Conditions

Smart mobile phones are susceptible to drop impact so the reliability of on-board packages under drop condition is a major concern to be addressed. For the efficiency of rapid prototyping, it is quite important that the product design, especially that of the main circuit board, is pre-examined in respect of its effect on the stress distribution In this study, finite element analysis is applied to investigate the effect of design factors of a mobile phone on the drop reliability of the on-board chip scale packages. Simulation results show that, screw pitch and area of shielding cover significantly affect the bending of PCB (printed circuit board), as smaller screw pitch and larger shielding cover resulted in the reduction of maximum principal stress in the silicon chip as well as in the critical solder joint by 20% to 30%. By using underfill, stress distribution in the solder became more uniform, and maximum principal stress in both chip and solder lowered than that without underfill. In addition, insufficient gap between the chip and front case might lead to collision, thereby causing the peak stress in the packages to increase significantly by about 30 MPa compared to the non-collision case. The research methods and results in this study are expected to provide guidance for the structural optimization in new mobile phone product design, as well as design-phase early screening of failure in the board-level assembly.