Accelerated determination of interfacial fracture toughness in microelectronic packages under cyclic loading

An accelerated and cost-effective characterization method for bi-material interfaces under cyclic loading using a Miniaturized Sub-Critical Bending (MSCB) test setup is presented. The Modified Single Leg Bending (MSLB) samples are acquired directly from production-line, Thin Quad Flat Package (TQFP). Under sub-critical cyclic loading, crack was found to occur at the polymer-metal interface. The crack length is measured using a numerical-experimental compliance-based method. In addition influence of temperature on interfacial adhesion properties namely, crack initiation and propagation is discussed. Sub-critical crack growth (SCCG) is captured along the surface between Molding Compound (MC) and copper Lead-Frame (LF). It is shown that crack propagation along MC/LF interface is highly fatigue sensitive. In addition the fatigue tests under different temperatures show that critical (G_c) and sub-critical strain energy release rate (G_th) are highly temperature-dependent. Finally the samples are fractographically examined using Scanning Acoustic Microscopy (SAM) and Energy-dispersive X-ray spectroscopy (EDX).