Fracture toughness characterization and modeling of interfaces in microelectronic packages - A status review

A review of several years effort to enable reliability prediction in microelectronic packages with respect to interface fracture under mechanical and thermo-mechanical stress loads is provided. Problems, solutions, results and links between activities are summarized. Methods and status to measure the critical energy release rate to propagate a crack G_c=G_c(Ψ(l_ref), T, C), especially its dependence on mode mix between tensile and shear load expressed by mode angle Ψ, but also on temperature T and moisture C are discussed. That comprises Epoxy Mold Compound to LeadFrame (EMC/LF), EMC/Si-chip and the status of glue Die Attach (DA/LF, DA/EMC) interface characterization. Measurement methods Mixed Mode Bending (MMB) in normal and harsh environment, advanced MMB, 4-Point Bending (4PB), Button Shear Test (BST) and Mixed Mode Chisel (MMC) are touched. Additionally a newly developed flMMT (Micro Mixed Mode Test) is presented, which enables interface characterization at small samples down to ~3mm length cut from real products. Also first time briefly presented is the development of physics based relations of mode mix dependency G_c(Ψ) instead of arbitrary data fitting. This reduces the huge effort needed to establish G_c(Ψ, T, C) data to acceptable levels for regular industrial application. Starting with a hypothesis, expressions for flat and roughened interfaces are derived. Comparing with data of the flat EMC/Si-interface even an expression for increasing chemical bonding is given, which can serve to distinguish physical and chemical contributions. The status review closes with a brief discussion of modeling options.