EFFECT OF COMPONENT HETEROGENEITY ON GLOBAL CTE MISMATCH DISPLACEMENTIN AREAL-ARRAY SOLDER INTERCONNECTS

An analytic model is developed for the problem of a thermally loaded e lectronic assembly consisting of a nonhomogeneous component attached t o a substrate by means of an areal of solder joints. The component is heterogeneous in the sense that the interior, or ''die'', portion and the exterior, or ''carrier'', portion may have different elastic modul i, different coefficients of thermal expansion, and/or different tempe rature excursions. Analytical results are presented for determining (a ) the location of the critical joint(s) in the array, defined as those experiencing the maximum shearing displacement due to global CTE mism atch, and (b) the magnitude of the maximum shearing displacement. The critical joint location and the (dimensionless) peak displacement are shown to depend on only two parameters: one involving the material, ge ometric, and loading characteristics of the component and substrate, t he other being the ratio of the die dimension to the array dimension. The stiffness of the solder array is neglected in the model; thus, the results should be valid for (a) thermal/power cycling of low-modulus solders (relative to component and substrate materials), and (b) high- temperature, low-frequency thermal/power cycling, for which a large de gree of stress relaxation occurs hr the solder. The results may also p rovide conservative estimates for situations involving stiffer arrays.