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Package Reliability of the SiC Power Modules in Harsh Environments
Keywords: High Temperature Packaging, Metalization of substrate and devices, SiC power modules
To develop the next-generation power converters with high power density using SiC devices, the high temperature packaging technology is crucial. The package substrate, devices and joint technology are the basic elements for packaging power modules. To evaluate the package reliability of the SiC power modules in harsh environments, the SiC Schottky Barrier Diodes (SBDs) were die bonded to the Si3N4/Cu/Ni(P) substrate with Au-Ge eutectic solder using a vacuum reflow furnace. The Al electrodes of the SiC-SBDs were connected to the Cu pattern with 250㎛-Al wires. The bonded samples were isothermally aged at 330℃ and tested under thermal cycling conditions in the temperature range of -40〜300℃ in air. During isothermal aging, cracks of the Ni(P) layer developed, resulting in oxidation of the Cu power path. The cracks are mainly caused by the precipitation of the Ni3P phase from the Ni(P) solid state solution, which leads to about 2-times increase in the hardness of the Ni(P) layer. Decrease in the die bond strength and increase in the electrical resistivity were observed due to the Cu power path oxidation and the growth of the Ni-Ge intermetalic compounds (IMCs) in the joint. Under the thermal cycling conditions, the metallization of the substrate suffers from serious surface roughness, which greatly degrades the die-attach reliability. The Al electrode was found to seriously exfoliate from the SiC-SBDs due to the thermal stress. After 521 cycles, almost all the whole Al electrode exfoliated form the anode. The non-wire bonding of the anode may protect the Al electrode form exfoliation. Benefit from the excellent mechanical properties of Si3N4, no delamination of the Cu layer was observed from the Si3N4 substrate after 1079 cycles, while the Cu layer delaminated from the AlN substrate only after 12 cycles.
Fengqun Lang, Research Scientist
National Institute of Advanced Industrial Science and Technology (AIST)
Tsukuba, Ibaraki, 305-8568,
Japan


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