Electronic assemblies are currently used in many applications in which more stringent reliability is required due to harsh operating environments. Premature mechanical failures and their consequential effects on electrical performance are often thermally-induced, and typically result from uneven expansions and contractions of the various assembly materials due to mismatches in the coefficients of thermal expansion. However, in addition to thermally induced stresses, electronic systems often experience vibration environments. These vibrations occur during shipping, handling and operation. The reliability of the electronic packaging under vibration is an important issue to the automobile industry. To assure high product reliability, it is necessary to provide estimating tools of vibration fatigue life to designers as early as possible in designing process. In this work, the reliability of the solder bump has studied by accelerated testing with torsional high-cycle fatigue loading. The fatigue-testing machine utilized a small-sized electromagnetic type actuator and personal computers for force signal generation and data acquisition. The specimen used in these experiments is PCB assembly having 32 BGA-type solder bumps. The PCB assembly is subjected to flexural fatigue tests at a frequency of 40 Hz. The time to failure is determined by the changes in the electrical resistance of solder joints. Based on the results of stress analysis using macro/micro model and the constant amplitude fatigue tests, the correlation of failure cycles N~f versus maximum equivalent stress range triangle open #sigma# _(eq-max) was obtained in high-cycle fatigue region within 10~4-10~7 cycle range. This accelerated test method could be efficiently used to estimate the high-cycle fatigue strength of solder bump.
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