Browsing UAF Graduate School by Author "Kasturi, Uday Bhaskar"
Analysis of a generic flip chip under shock and vibrationKasturi, Uday Bhaskar; Chen, Cheng-fu; Butcher, Eric; Lin, Chuen-Sen (2004-12)A flip chip package, underfilled or non-underfilled, was analyzed under mechanical shock and/or vibration at the device and board levels, respectively. For the tests at the device level, the maximum stress developed at the corner-most solder joint. The horizontal drop orientation, with the chip facing up, produced the worst scenario for solder joint lifetime prediction. The underfilled package is better than non-underfilled under the excitation of mechanical shock and vibration. Parametric studies of the underfill material strength suggested that the higher the elastic modulus, the better it carried the mechanical shock. However, practically the upper bound of the elastic modulus is limited to avoid die cracking due to thermal mismatch of material expansion. The combined loading of thermal residual stress and mechanical shock was also conducted to study their influence on the solder lifetime prediction. It was found that the thermal pre-stressed condition plays a key role for the von Mises stress excursion, but has almost no influence on the shock-induced normal stress. The phenomenon appears similarly in the board level testing, but with worse reliability in solders due to the higher stresses induced.