Interface and interconnection stresses in electronic assemblies - A critical review of analytical solutions.

The closed-form solutions for the interfacial stresses in assemblies constituting of two relatively stiff adherends sandwiching a relatively compliant adhesive layer are reviewed. The closed-form solutions are categorised into the “non-free edge solutions” that do not satisfy the nil-shear stress condition at the free edge of the adhesive and the “free edge solutions” that do. Being strength of material solutions, the non-free edge solutions are significantly simpler in form. On the other hand, the solutions tend to grossly underestimate the magnitude of the peeling stress at the free edge. Almost all classical “non-free edge solutions” suffer from two setbacks: (i) assumed σa=0, thus severely underestimating the magnitude of the peeling stress; and (ii) neglected the thickness of the adhesive in their formulation of the x-compliance of assemblies and the evaluation of the effective bending strain on adherends; the former leads to overestimation while the latter leads to gross underestimation of the shear stress (and hence, σa(l)). These are demonstrated in a numerical exercise in which two widely followed “non-free edge solutions” and a simplified “free edge solutions” are benchmarked against the finite element analysis.