SiC power devices packaging with a short-circuit failure mode capability

Abstract

The failure mode of press-pack-type packages dedicated to SiC devices is experimentally analyzed in order to investigate their use for HVDC applications. Single SiC Schottky diode samples have been submitted to short-circuit conditions and continuous current flow test. The samples have been then characterized with optical and scanning electronic microscopy. Results from the experiments reveal that the press-pack structure offers a short-circuit failure mode with SiC devices, as it does for Si devices. The metallurgy involved is, however, quite different. Cu, Ni, Ag or Al foils are found to be suitable interface material between the package and the die to achieve a stable a short-circuit failure mode, providing the die is properly attached to a substrate.

Packaging Solution for SiC Power Modules with a Fail-to-Short Capability

“…The measured resistances tend to be high compared to the R DSon of the MOSFETs (25 mΩ). This was also observed on single die tests [6], and is related to the metallurgy of SiC: for Si devices, the failure test causes the semiconductor material to melt and form a conductive alloy [3]. SiC does not melt.…”

“…This ensures a good performance interconnection (silver sintering offers excellent thermal and electrical conductivity [8]). Furthermore, as presented in [6], silver was found to be a suitable contact material to achieve fail-to-short behaviour with SiC devices. It is worth noting that no additional element (spacer, balls, etc.)…”

“…As demonstrated in [6], interconnects made of copper or silver offer the best performance (lower resistance) for a failto-short package. Here, the interconnects are provided using a "sandwich" structure, where the semiconductor dies are placed between two direct bonded copper (DBC) tiles ( Fig.…”

“…Each packaged MOSFET is then submitted to a surge current test, using the circuit depicted in Fig. 8a (and detailed in [6], [12], [13]). An example of the current and voltage waveforms acquired during the surge test is presented in Fig.…”

“…Recently, it has been demonstrated that while SiC devices do not melt in case of failure, the SiC dies shatter and the surrounding metal interconnects can infiltrate in the cracks, forming a conductive path [6]. Based on this observation, a multi-chip power module is proposed in this article.…”