Epoxy Molding Compound Interface Research Articles

Fatigue crack propagation in a copper/epoxy molding compound interface as impacted by mode-mixity

Microelectronic packages contain numerous bimaterial interfaces which influence both device design and reliability. The failure of these bimaterial interfaces have been observed to be a function of both the relative shear and tensile loads, otherwise referred to as “mode-mixity.” While the failure of such bimaterial interfaces has been the focus of much study, their performance under fatigue, in particular with respect to mode-mixity, is underexplored. Double cantilever beam tests for a copper /epoxy molding compound interface have been performed for several different mode-mixity conditions, both monotonically and cyclically. The resulting Paris’ laws are reported. In particular, the impact of mode-mixity on fatigue crack propagation is explored. The Paris’ law coefficients and exponents have been seen to be dependent on mode-mixity. The dependency of fatigue behavior on mode-mixity means that some of the properties of fatigue crack propagation can be determined from a bimaterial interfaces monotonic fracture behavior. Finally both numerical analysis in ANSYS and SEM surface characterization are performed to further the understanding of the mechanisms behind the observed trends in fatigue interfacial delamination propagation behavior as a function of mode-mixity.

Adhesion improvement of Cu-based substrate and epoxy molding compound interface by hierarchical structure preparation

For microelectronic industry, Cu-based substrate and epoxy molding compound (EMC) interface is inherently weak and most likely to delaminate, well-known as a major threat for integrated circuits (ICs) reliability. In this paper, hierarchical whisker-like oxide/Cu cone structure was for the first time to be fabricated by combining electroless plating with heat treatment methods to enhance the interface adhesion between Cu-based substrate and EMC. The surface morphology was characterized by scanning electron microscope (SEM). Result shows that the hierarchical whisker-like oxide/Cu cone film is fine, dense and uniform; Single Cu cone structure is about 3–5μm in height and 1μm in root diameter; a layer of whisker-like oxide grows perpendicularly to circular surface of Cu cone, with length ranging from tens to hundreds of nanometers. Adhesion strength between the as-prepared substrates and EMC were measured by button shear test. With consideration of oxidation caused by practical processes (e.g. wire bonding), the interface of EMC and porous oxide formed at 260°C for 5min was taken as standard sample, representative of practical interface. To further study the effect of whisker-like oxide and Cu cone solely on adhesion performance, whisker-like oxide, porous oxide/Cu cone were investigated as well. Button shear test results reveal that interfacial adhesion strength of EMC and whisker-like oxide, porous oxide/Cu cone, hierarchical whisker-like oxide/Cu cone are 85%, 110% and 162% higher than that of standard interface. Moreover, the mechanism for adhesion improvement was discussed by facture surface observation, failure path assumption and force–displacement curve analysis. Results show that interface of EMC and hierarchical whisker-like oxide/Cu cone exhibits brittle/ductile property with about 3–5μm thick EMC left on the fracture surface, indicating cohesive failure caused by remarkable mechanical interlocking effect.

Fracture of copper-based leadframe/EMC interfaces

Copper-based leadframe sheets were oxidized in a black-oxide forming solution and molded with epoxy molding compound (EMC) to measure the fracture toughness of leadframe/EMC interface using sandwiched doublecantilever beam (SDCB) and sandwiched Brazil-nut (SBN) specimens. Results showed that the pebble-like Cu2O precipitates on the leadframe had almost no adhesion to the EMC, while the opposite was true for the acicular CuO precipitates. Under the mixed mode loading, the fracture toughness increased parabolically with the phase angle (ψ) while minimum at ψ=0°. For ψ<-34°, the interface crack kinked into the EMC. Fractography analyses based on XRD, AFM, SEM and AES studies showed that the failure path along the leadframe/ EMC interface varied significantly with the surface condition of the leadframe prior to the molding process and the loading condition.