Thermal stress analysis and design optimization of direct chip attach (DCA) and chip scale package (CSP) in flip chip technology

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Underfill encapsulation is a technique used to reinforce the solder bumps between the chip and the substrate in flip chip technology. To determine the optimal geometrical parameters and material properties for the package and candidate underfill materials is an important strategy for improving the thermo-mechanical reliability of flip chip packages. In this study, a stress-function-based energy method was developed to evaluate the interfacial peel and shear stress distributions in multilayered packaging structures. The stress functions were expressed in terms of sine and cosine trigonometric series. Simple programming and short CPU time lead to accurate stress distributions. After comparisons with other proposed numerical methods and results, the developed model was then coupled with a Genetic Algorithm to optimize the design of the direct chip attach (DCA) and chip scale package (CSP) in order to diminish the interfacial stresses and the possibility of crack initiation. The results revealed that the maximum peel and shear stress values were productively decreased and their peaks moved toward the center after conducting the optimizations in both cases. Improved geometrical and material parameters of the flip chip package were determined.