Sandwich Double Cantilever Beam Research Articles

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.

Effects of oxidation treatments on the fracture toughness of leadframe/epoxy interfaces

A copper-based leadframe is oxidized in two types of alkaline solutions; one forming brown oxide and the other forming black oxide, and molded with epoxy. SEM and X-ray studies on the surfaces of oxidized leadframe and fracture-toughness measurements by using sandwiched double-cantilever beam (SDCB) specimens showed that the interfacial fracture toughness is directly related to the formation of acicular CuO precipitates at the interface. However, once a continuous layer of CuO precipitates formed on the leadframe (brown oxide) or the underlying Cu2O layer (black oxide), interfacial fracture toughness saturated regardless of further oxide thickening. The size of the acicular precipitates was found to have secondary effects on the interfacial fracture toughness.

Adhesion strength of leadframe/EMC interfaces

Cu-based leadframe sheets were oxidized in alkaline solutions to produce brown and/or black oxide on the surfaces, and molded with epoxy molding compound (EMC). The adhesion strength of leadframe/EMC interface was measured using sandwiched double-cantilever beam (SDCB) specimens and pull-out specimens. Results showed that the adhesion strength of leadframe/EMC interface was inherently very poor but could be increased drastically with the nucleation of acicular CuO precipitates. The presence of smooth-faceted Cu2O on the surface of the leadframe gave close to zero fracture toughness (GC) and suitable pull strength (PS). A direct correlation between GC and PS showed that PS can be a measure of GC only in a limited range.

Effects of chemical oxidations on the fracture toughness of leadframe/EMC interfaces

Cu-based leadframe sheets were oxidized by a chemical oxidation method, which formed two kinds of oxides on its surface, a brown one and a black one. The oxidation characteristics of each oxide were studied and then to measure the adhesion strength of the leadframe/EMC interface as a function of fracture toughness, the oxidized leadframe samples were molded with an epoxy molding compound (EMC) and machined to form sandwiched double-cantilever beam (SDCB) specimens. SEM and XRD studies on the surfaces of the oxidized leadframe as well as the measurement of fracture toughness showed that the interfacial fracture toughness is directly related to the formation of acicular CuO precipitates on the surface of the leadframe. However, once a continuous layer of CuO precipitates formed on the surface of the leadframe (brown oxide) or on the Cu2O layer (black oxide), the interfacial fracture toughness is found to saturate regardless of a further oxide thickening. The size of the acicular precipitates seems to have a secondary effect on the interfacial fracture toughness.

Measurements of the Adhesion Strength of Cu/Epoxy Interfaces

ABSTRACTCopper-based leadframe sheets were oxidized in a black-oxide forming solution, molded with epoxy molding compound (EMC), and the interfacial fracture toughness was measured using sandwiched double cantilever beam (SDCB) and sandwiched Brazil-nut (SBN) specimens.Results showed that pebble-like Cu2O precipitates on the leadframe had almost no adhesion to EMC while the opposite was true of the acicular CuO precipitates. Thus, the fracture toughness of the leadframe/EMC interface was close to zero in the beginning but rapidly increased to ˜100 J/m2 as acicular CuO nucleated on the smooth-faceted Cu2O layer. Under the mixed Mode loading the fracture toughness increased parabolically with the phase angle (ψ) with minimum at ψ = 0°. For ψ &lt; -340, interface crack kinked into EMC. Fractography analyses based on XRD, SEM and AES studies showed that the failure path along the leadframe/EMC interface varied significantly with the loading condition and the crack speed.

New adhesion measurement technique for coated cutting tool materials

Adhesion properties of wear resistant coatings on cutting tool materials are essential to their performance in technical applications. It is therefore necessary to characterize the coating adhesion by an appropriate measurement technique which reveals both critical adhesion values as well as information on time dependent debonding. In particular, a quantitative and reproducible technique is required rather than largely qualitative methods such as indent or scratch tests. In addition, for multilayer coatings, the location of the weakest interface is required to facilitate improvement of interfacial integrity. Accordingly a sandwich double cantilever beam (DCB) test was developed and used to measure the adhesion properties of coatings on cermets. Additionally, the structure of the coatings in the as fabricated state and after mechanical testings were characterized by optical microscopy, SEM and TEM. With quantitative adhesion measurements and investigations of the interface microstructure, a comprehensive characterization of coating adhesion on cutting toolmaterials was achieved.

Fatigue crack propagation along polymer-metal interfaces in microelectronic packages

In this study, a fracture mechanics-based technique was used for characterizing fatigue crack propagation (FCP) at polymer-metal interfaces. Sandwich double-cantilever beam (DCB) specimens were fabricated using nickel and copper-coated copper substrates bonded with a thin layer of silica-filled polymer encapsulant. Under cyclic loading, crack propagation was found to occur at the polymer-metal interface. The interfacial failure mode was verified by scanning electron microscopy (SEM) analysis of the fatigue fracture surfaces. The crack growth rate was found to have a power-law dependence on the strain energy release rate range, and exhibited a crack growth threshold, much like the fatigue crack growth threshold stress intensity factor range for monolithic bulk metals, polymers, and ceramics. Interfacial FCP data for three candidate encapsulants predicted cracking resistances that were well correlated with package-level reliability tests. By varying the surface roughness of the copper and nickel plating, it was shown that interfacial FCP resistance increased with increasing roughness. The observed increases in FCP resistance were attributed to a reduction in the effective driving force for fatigue fracture along the rougher interfaces, and could be accounted for by a crack-deflection model.