An improved miniature mixed-mode delamination setup for in-situ microscopic interface failure analyses

Precise characterization of interface delamination in miniature interface structures is an ongoing challenge with the advent of miniaturization and multi-functionality in the electronics industry. Accurate numerical prediction of the interface behavior is necessary to minimize delamination failures. Successful prediction requires (i) accurate determination of the interface properties like the critical energy release rate, CERR, over the full range of mode mixities and (ii) simultaneous in-situ microscopic visualization of the delamination mechanism. These requirements were recently addressed by the development of the miniature mixed mode bending (MMMB) setup [Kolluri et al., Int. J. Frac. 2009]. In this article an improved MMMB setup is presented, which overcomes the main limitations of the original design. Specifically, the improved design (i) can access a significantly larger range of interface systems due to its increased limits of maximum accessible load and stroke in all mode mixities, (ii) has significantly higher accuracy in load-displacement measurement due to its reduced clearance at the connectors, which is particularly relevant for miniature samples, and (iii) has a high reproducibility due to a newly added setup alignment tool. The measurement concept is validated on (industrially relevant) copper lead frame-molding compound epoxy (CuLF-MCE) interface structures. The load-displacement curves and corresponding CERR values obtained from experiments over the full range of mode mixities are discussed in relation to the delamination mechanism observed during real-time in-situ isualization. Specifically, the measured increase of the CERR towards mode II is related to a more discrete or jerky crack growth behavior observed in the mode II dominant tests. Finally, the potential of the methodology for interface parameter characterization is illustrated.