Board level reliability of a stacked CSP subjected to cyclic bending

Second (board) level reliability of a stacked chip scale package (SCSP) under cyclic bending is conducted to evaluate the structural integrity of solder interconnects. The test vehicle (on-board SCSP) is simply supported at both ends and subjected to repetitive deflection in the middle (three-point bend). Cyclic deformation histories such as sinusoidal, triangular, and square waveforms are examined. Tremendous joint damage is observed as square-wave loading history was applied. Approximately 80% fatigue life degradation is found by bending several thermally aged samples having Ni/Au surface finish on Cu pads of package substrates and printed circuit boards. The observed failure mode is a brittle type fracture of intermetallic compound system, which is also known as effects of solder embrittlement.Measured fatigue life is characterized by two-parameter Weibull model with cumulative damage plot for each test condition. In addition to the comparisons of characteristic fatigue life for various package configuration and cyclic bending conditions, failure analysis is also employed to identify failure sites and mechanisms such as crack initiation and continuous growth to the complete fracture of solder joints. [Copyright &y& Elsevier]