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.
Experimental study of cold gas spraying through a mask. Part 1
The paper presents experimental data for production of a coating using cold gas dynamic spraying with a mask with transverse size in the range 0.3–1 mm and placed at different distances from the substrate. The coated samples were produced, and coating profiles were measured in the vicinity of the masked zone. The tests with depositing of aluminum powder and copper powder demonstrated that the distinct profile of masked zone is obtained for placing the mask at a distance below critical (depending of spray conditions). The most accurate boundary of the masked zone takes place at a minimal distance (depends on the coating thickness). Depending on the spraying conditions, the increase in the mask-substrate distance may result either in monotonic decline of the masked zone width or a slight increase for a certain range. Experimental data are generalized by normalizing with the transverse size of the mask (under other equal conditions).
Adiabatic shear instability based mechanism for particles/substrate bonding in the cold-gas dynamic-spray process
Particles/substrate interactions during the cold-gas dynamic-spray deposition process are studied using a dynamic axisymmetric thermo-mechanical finite element analysis. In addition, the particles/substrate bonding mechanism has been investigated using a one-dimensional thermo-mechanical model for adiabatic strain softening and the accompanying adiabatic shear localization. The results obtained show that the minimal impact particles velocity needed to produce shear localization at the particles/substrate interface correlates quite well with the critical velocity for particles deposition by the cold-gas dynamic-spray process in a number of metallic materials. This finding suggests that the onset of adiabatic shear instability in the particles/substrate interfacial region plays an important role in promoting particle/substrate adhesion and, thus, particles/substrate bonding during the cold-gas dynamic-spray process.