Device Packaging 2019

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Reliability & Characterization of Wide Band Gap Power modules using POL-kW Packaging technology
Keywords: Power Overlay, Power electronics Packaging, SiC
Introduction: As Wide Band Gap power semiconductor devices continue to mature for market adoption, innovative power electronics packaging designs and materials are needed to achieve the power density and efficiency that WBG devices are entitled to. Wire bonding loops are one of the major limiting factors in traditional module packaging methods to taking full benefit of WBG devices’ superior electrical and thermal properties. Wire-bondless packaging methods have been demonstrated with low losses and to allow integration of the gate drive circuit. In this paper, a wire-bondless packaging platform, referred to as Power Overlay Kilowatt (POL-kW), for WBG devices is presented. Description of POL and POL-kW: The main feature of the POL technology is a polyimide-based “chip-first” planar, copper interconnection structure, using electroplated, filled vias through a layered polyimide/adhesive structure to make electrical connections to the device bond pads. The via interconnects offer significantly reduced parasitic inductance and resistance, while providing a thin profile and high packaging density. The schematic and SEM image below show cross-section views of a typical POL construction. The POL structure uses a 1-2mil thick polyimide-based substrate with a 10-20um adhesive layer followed by a direct metal interconnect formed by sputter and plating methods. The adhesive layer is used to attach the dies to the polyimide film. Copper vias are formed by laser drilling, followed by sputtering and electroplating to form vias to the semiconductor dies and simultaneously form electrical interconnect routings on the polyimide surface. A power ceramic substrate, e.g. direct bond Cu (DBC), is attached to the bottom side of the POL structure using a Pb-free solder alloy. An underfill is applied around the WBG dies for electrical isolation and mechanical strengthening. The focus of this paper is on the POL-kW packages, which are intended for high power applications, for example 180A, in motor drives and power conversion, in the automotive, aerospace and renewable industries. Technical Content: In this paper we will give a technology update and status of GE’s POL -KW packaging technology for High Power modules. Process flow and production details will be summarized, to provide a better understanding of the technical and performance advantages. We will discuss the transition from R&D to commercial sources and the status of each. Quality and process capability will show a production ready technology. Here an MRL assessment will be made and demonstrated process examples will be shared. Test modules were fabricated and tested, to verify electrical and mechanical reliability. Analysis of these modules will be reviewed, including the topics of power cycling, high temperature storage, temperature & humidity testing. POL-kW modules resulted in substantially reduced parasitic losses, compared with aluminum wire bonds, hence significantly reduced switching losses were achieved. A preliminary cost model has been constructed to compare POL-KW with conventional wire/ribbon bonded modules. Possible Application areas will be discussed and then followed by GE module examples. Electrical characterization of these modules will be shared. E.g. half bridge module; Rds(on) simulation vs. measure; switching waveforms; thermal analysis, etc. Lastly, other areas of interest for POL based packaging will be discussed, such as embedded, LED and 5G applications. Summary: WBG power devices have the potential to achieve higher power density, reduced module size and weight. However, the traditional module packaging methods still limit their full potential at the module and system levels. One of the major causes of parasitic losses is wire-bonding loops. The wire-bondless packaging platform of POL-kW presented in this paper aims to eliminate the shortfalls associated with wire bonds, and to take advantage of WBG power devices’ superior electrical and thermal properties. POL-kW utilized polyimide-based Cu via interconnection to replace aluminum wire bonds and resulted in much reduced parasitic resistance, capacitance and inductance, compared with aluminum wire bonds. The POL-kW packaging platform was demonstrated as a critical enabler for WBG power modules to operate with lower losses and higher power density than traditional Si modules. Data presented in this paper has shown the progression of the technology from R&D to commercial manufacturing lines.
Christopher Kapusta, Process Development Engineer
General Electric
Niskayuna, NY

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