Development and Testing of Cold gas Sprayed Circuit Boards for Power Electronics Applications
Within the framework of the presented project, new mounting concepts for power electronics were implemented by applying Al/Cu coat systems to insulators by means of cold gas spraying (CGS). The layers sprayed with cold gas were investigated and good material properties are observed. The applied metallizations show an extremely small porosity, no thermally induced phase conversions or process-related oxides and a high adhesive strength. Also the processing of assemblies with standard processes such as a soldering, adhesive bonding and heavy wire bonding is possible. The temperature shock stability of the new substrates was determined in temperature cycle experiments and it was compared with the temperature shock stability of the DCB substrates. The substrates were tested actively but also passively in bicameral temperature shock chamber and in power cycling experiments at power electronic function samples. The accomplished reliability investigations showed that the characteristic lifetime of the cold gas sprayed substrates is approximately 80% of the characteristic lifetime of the DCB substrates. These demonstrate that the substrates produced in cold-gas technology can be used for power electronic applications.
Investigation of modern electrically conductive adhesives for die-attachment in power electronics applications
In the year 2006 a ban of lead containing solders in the EU required the qualification of lead-free solder alloys. However, these do not provide the same characteristics as lead containing solders do. Also their costs are higher due to expensive machinery use and increased tin and silver contents. The aim of our research is to develop assemblies based on electrically conductive adhesives that have better characteristics than solder. In this paper three electrically conductive adhesives are investigated. Their thermal and electrical conductivities are compared to the respective properties of solders. In addition mechanical analyses are accomplished so that adhesive strengths on several substrates can be compared even after aging and fatigue. Overall, this work showed that electrically conductive adhesives can be an alternative to solders for the conductive assembly of high-power devices.
Formation and Strength of Magnesia Whiskers
The formation of single-crystal magnesia whiskers during the compressive deformation of single crystals at room temperatures is described. These whiskers can have strengths of the order of millions of pounds per square inch. They are formed during fracture as a result of the discontinuous propagation of cracks which are mechanically relieving internal stresses resulting from plastic flow