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|Product Development of High Power Electronics (from 600v to 1200V) for High Reliability Applications|
|Keywords: Silicon Carbide (SiC), High Power Electronics, High Temperature|
|Silicon Carbide (SiC) power electronic devices have the attributes of heat resistance, radiation tolerance against total ionising dosages , high breakdown voltage and high operating frequency, all of which are excellent attributes for this technology to operate in harsh conditions. However, there is room for improvement. For example, one of the constraints of today’s High Power Electronic Device (HPE) manufacturing is the RoHS guidelines which must adhere to when manufacturing SiC components. It is our aim to keep looking for improvements in these devices so we can continue to get closer to the full potential SiC products can offer to the Hi-Rel industry. The goal of this study was to achieve an improvement in power conversion based on SiC HPE at high temperature devices. This was achieved by building upon existing underpinning research from materials science and fabrication technology of SiC, in particular, Diodes (600V & 1200V with an absolute maximum current of 10A) and Mosfets (600V & 1200V with an absolute maximum current of 20A). The approach consisted of finding the optimal build from an array of different variables; from materials to technologies, all which would allow improving the performance of HPE devices under harsh environment (low(-65°) & high(220°C) temperatures, deep thermal cycling, vibration, etc.). The joining processes and the material selection of the components were carefully planned, taking into account the current literature, eight different builds were considered. All the experiments were carried out in accordance with MIL-PRF-38534 & MIL- PRF-19500P standards with the goal to improve the current limitations that compromise both the performance and resilience of an HPE device under harsh conditions. Furthermore, the appropriate metallographic techniques were used for auxiliary analysis. Results show the HPE devices manufactured reached the following figures on average for the eight builds altogether: wire bond strength was 430% above minimum requirement; die/substrate and substrate/package attachment strength passed the minimum shear requirement; taking into consideration the V[F] and I[R] limits from the die’s specification at ambient temperature (typical V[F]=1.5V being the limit V[F]=1.8V and typical I[R]=50µA being the limit I[R]=200µA) the eight builds on average reached F[V]= (1.586±0.062)V & I[R]]= (3.501±3.786)µA (n=48). The best build out of the eight different builds achieved: at ambient temperature F[V]= (1.517±0.037)V & I[R]]=(0.056±0.030)µA (n=6); at ambient temperature after temperature cycling: F[V]= (1.563±0.006)V & I[R]]=(0.056±0.009)µA (n=3); at 220°C F[V]= (3.116±0.057)V & I[R]]=(10.126±4.071)µA (n=6). The tight difference between the F[V] of the probed die and the F[V] of the assembled device is a very positive achievement, as it proves the success of this project, since the electrical resistivity consequent by the assembly of the die in a package was minimized. Out of the pool of multiple materials and technologies used and applied, it was possible to obtain an ideal bill of materials and respective process for the manufacturing of HPE devices well suited for the Hi-Rel applications that takes into consideration their cost- effectiveness.|
|Tiago Loureiro Teixeira, Project Engineer