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.
Silica in Soils1
Publisher Summary Silica in free and combined forms is a dominant component of the solid material of many soils, and dissolved silica is commonly a major solute of soil solutions. Breakdown of primary silicates, translocation of silica in solution, and deposition of secondary silica-containing substances are involved in the development of soils. Ions essential for the growth of plants are released to the soil solution as silicates weather, and these ions may be held against leaching at exchange sites on other silicates. Silica is absorbed in appreciable quantities by some plants and is returned to the surface of the soil as the plants decay. The nature and transformations of silica and silicates in soil are, thus, fundamental to an understanding of many aspects of soil and plant sciences.