Simulation assisted investigation and improvement of the performance of an electronics assembly subjected to temperature cycling
Numerical simulation techniques are used increasingly in the (re-)design of micro-electronics because of their time and cost saving potentials. The current paper describes the application of such techniques for analysing and improving the thermo-mechanical performance of an electronics assembly. An initial finite element model is implemented and its predictions are compared to measurements. Based on this comparison, the model is further refined by an improved assessment of the input to the model in the form of materials properties: the properties of the moulding compound, failure behaviour of the lead-compound interface and failure behaviour of the lead material itself. Finally an updated model is used to determine directions for improvement of the behaviour of the assembly design.
Fatigue behaviour of Fe–Cr–Si–B metallic glass wires
Abstract Cyclic compressive/tensile bending has been carried out on Fe–Cr–Si–B metallic glass wires using a controlled strain double pulley testing machine. The fatigue performance of two series of glassy alloy wires Fe 78−x Cr x Si 10 B 12 and Fe 77.5−x Cr x Si 7.5 B 15 have been compared with those of HT steel wires. Because of differences in modulus, the ranking of the materials studied changes according to whether the results are reported in terms of stress or strain. In terms of stress, the HT steel wire had a superior fatigue performance to the glassy wires; however, in terms of strain, the Fe 69.5 Cr 8 Si 7.5 B 15 glassy wire, under higher cycle conditions, had a superior fatigue performance, to HT steel wire. The fatigue performance of the glassy wires improved with the partial substitution of Fe by Cr. The short fatigue life of the glassy wires containing zero or low Cr contents in the present study was at least partly due to the necked morphology along their lengths. Fractography revealed that corrosion pits nucleated on the surface of the wires and resulted in crack initiation at these points.
On the fracture morphology of metallic glasses
Abstract The perturbation theory, developed by Mullins and Sekerka to describe instability during crystal growth, has been applied to the problem of the fracture of the liquid layer formed during the deformation of a metallic glass. A relation between the fracture stress and the fine features of the fracture morphology is predicted, in agreement with experimental results.