Board Level Drop Test and Simulation of CSP for Handheld Application

Abstract

For CSP used in handheld electronic products, such as mobile phone, PDA, etc., the board level drop test has become a great concern, especially in the stage of lead free transition.Comparison between SnPb and lead free Sn4AgO.5Cu solders, CSP components on board with SnPb solder had much better drop test reliability than lead free one. However, since the drop test is a time-wasting method, the simulation technique is necessary to shorten the design stage and get the optimized solution. In current study, LS-DANA was used to do stress simulation during drop impact. In the beginning, the PCB strain response was compared between modeling and drop test. The result showed good agreement with -maximum 15% deviation. The stress in the solder joint was also analyzed and the high stress area in component side was similar with failure mode confirmed by dye and pry analysis after drop test.The simulation technique was also used to confirm the effect of ball layout on the drop test reliability in this study. In the modeling, the peeling stress decreased with increment in row number of outer solder balls till 3 rows. As row number larger than 3, no big difference was found. In drop test, the result also showed the similar trend. Comparison between 2 and 3 rows, both SnPb and Sn4AgO.5Cu could not pass 30 drops with 2 rows, but 3 rows could effectively improve the reliability to pass 30 drops.

Mechanical properties and joint reliability improvement of Sn-Bi alloy

“…And an impact life prediction model based on maximum peeling stress of critical solder joints is proposed for board level drop test to estimate the number of drops to failure [8][9][10][11].…”