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Improved Direct Bond Copper (DBC) Substrate for High Temperature Packaging

Fig. 1. Sealing the stepped edge DBC substrate.
In recent years, the SiC Power semiconductor has emerged as an attractive alternative that pushes the limitations of junction temperature, power rating, and switching frequency of Si devices. However, there is no available commercial packaging can support the high temperature operation. In order to take the advantages of SiC devices, researchers have put their focus on the power module packaging for high temperature.

Substrate is the fundamental component in the wirebond package. With a detailed survey and investigation, the Aluminum Nitride DBC (AlN DBC) was chosen as the substrate for high temperature power module. The aging test showed that AlN DBC can support 250°C operation. However, in the large temperature excursion test (from -55°C to 250°C, 45 minutes per cycle), the AlN DBC failed just in 20 cycles. As show in Fig.1 CPES proposed a method to improve the thermo-mechanical reliability of DBC substrate by utilizing polyimide Epo-tek 600 to seal and strengthen the stepped edge DBC substrate. As show in 2, 6 samples fabricated and all sealed edge samples passed 800 cycles. Three of them failed at 850 cycles and two of them failed at 1200 cycles. Fig.2 also shows the cross-section of the sample after 1100 cycles under microscope. It can be noticed that the copper and ceramic were bonded well without any peeling off.

By taking advantage of the CPES sealed stepped edge method, the thermo-mechanical reliability of DBC substrate can be significantly improved. With improved DBC substrate, high temperature power module will have long lifetime in harsh temperature excursion.

Fig. 2. Thermo-mechanical reliability test results.
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