Mechanistic figures of merit for die-attach materials

Delamination and/or rupture of the die-attach layer are among the primary failure mechanisms in plastic IC packages and often lower the threshold for other mechanical, as well as electrical, failure mechanisms. Die-attach failure is generally caused by the thermal expansion (contraction) mismatch of dissimilar materials and the consequent development of axial and shear stresses in the adhesive and along the material interfaces. To enhance the reliability of plastic packaging it is thus desirable to select the most reliable and cost-effective die-attach material. Analysis of an ideal tri-material structure, using a force and momentum balance, makes it possible to derive analytical relations for the axial and shear stresses in a die-attach layer. Based on these analytical relations, which are validated against FEM results, the critical material properties can be selected and used for the development of Figures-of-Merit (FOM) for material selection. These FOMs are then used to evaluate the effects of moisture on the selection of the die-attach materials