SOLDER JOINT RELIABILITY AND FAILURE ANALYSIS OF LFBGA ASSEMBLIES

摘要

In the normal life span of portable electronic products such as cellular phones, PDA, and game stations, the number-dialing strikes cause a bending effect on the print circuit board (PCB). This PCB flexing forces the solder balls under a condition of fatigue loading and repetitive stresses as well. Therefore integrity of second level interconnects subjected to cyclic bending becomes a major concern before the application of packages into products. In this work, bending cyclic test (three-point bend) is conducted to investigate the reliability of on-board LFBGA assembly. It is observed that maximum deflection of PCB and vibration frequencies play very important roles on the fatigue life performance of solder balls. Hence three different vibration conditions (2mm/2Hz, 2mm/1Hz and 1mm/2Hz) are selected in this paper to evaluate their impact. In addition, the effects of package configuration such as die size and stand-off are also examined. All solder joints of a test vehicle are daisy-chain connected to form a continuous loop. Real-time electrical resistance measurement is implemented to determine the failing cycles of a test vehicle. The two-parameter Weibull model is applied to characterize the fatigue life for all experiments. Failure analysis of the solder joints is also performed to identify the failure sites as well as fracture modes of the joints.