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.
Novel cooling technology to reduce thermal impedance and thermomechanical stress for SiC application
Silicon carbide (SiC) device is suitable for high temperature application. However, due to the high Young's Modulus of SiC material, the power cycling capability of SiC device is weak in harsh environment. To enhance the reliability of SiC devices, the thermal interface material (TIM) should have high thermal conductivity and long-term reliability. The cold spray low temperature soldering (CS-LTS) is an advanced technology for TIM instead of grease. It can reduce the thermal resistance of a power electronic system, and ensure the superior performances of TIM in long-term working condition. In this paper, the novel cooling technology is proposed for SiC application by using CS-LTS as the TIM. To evaluate the thermomechanical performance and lifetime of the advanced SiC device system, 2-D finite element analysis (FEA) simulation model and experimental set-up are established. The transient thermal resistance obtained from simulation model is in good agreement with the experimental results. The results indicate the thermal resistance and stress of CS-LTS-based system is much lower than that using grease. Besides, the novel cooling system is also verified with excellent reliability in power cycling evaluation, and it is appropriate for SiC application in high-temperature and high-power-density converters.
Experimental study on bond behavior between high-strength grout and deformed steel bars
Abstract Engineers use high-strength grout to connect precast concrete members for its low shrinkage and good fluidity. This paper designed 87 central pull-out specimens using the control variable method to investigate the influence of factors on the rebar-grout bond property such as compressive strength, steel grade, bar diameter, transverse stirrups, and bond length. The test result showed that improving grout compressive strength (85.8 MPa–122.7 MPa) cannot improve the bond strength, which was different from the previous conclusions of concrete pull-out tests. Simplified formulas were presented for calculating the characteristic values of bond strength, residual strength, peak slip, and relative slip of load-holding platform based on parameter analysis. Then, a constitutive model was proposed to predict the full-range bond stress-slip curve of high-strength grout and steel bar specimens from bearing to failure. Finally, FEA models were established to evaluate the applicability and accuracy of the constitutive model.