Douglas C. Hopkins

Misconception of thermal spreading angle and misapplication to IGBT power modules

This paper analyzes the widely used 45 degrees thermal spreading model in IGBT package design and quantifies error in application to both single and multilayered package structures. The results are compared with finite element analysis (FEA). For single-layer heat transfer problem, the spreading angle model with a 45 degrees assumption provides a less than 20% conservative error of thermal resistance for a certain substrate layer thickness range, but is not applicable to multi-layered structures. For two or more layered structures, as commonly found in direct bonded copper (DBC) substrates and used in multiple-chip power modules (MCPMs), the 45 degrees fixed-angle method cannot capture the behavior of the heat transfer problem nor accurately predict the temperature of critical points for design. The method introduces substantial underestimation of junction temperature dependent on layer thickness ratios. An in-depth literature review was conducted and little, if any, concrete basis for the 45 degree assumption was found. Guidelines for using more accurate spreading-angle calculations are provided for the practice engineer.

Results for an Al/AlN composite 350°C SiC solid-state circuit breaker module

This paper describes final results for the verification and testing of a SiC MOSFET-based solid-state circuit breaker power module for ultra-fast current interruption. The module exhibited a single-die (4.1mm × 4.1 mm) 48 A, 5 ms trip point from a 300 V bus with a di/dt of 2.1 kA/us (23 ns opening time). An internal snubber increased the response to 390 ns. The die absorbed ~4.6 J causing a transient junction temperature increase of ~245 °C. Ambient was set at 25 °C and 105 °C. Hence, maximum junction temperature was conservatively projected to reach 350 °C during the 5 ms pulse. An Aluminum composite structure was used for high temperature thermal management and high reliability. Testing of the final module surpassed 750 total cycles. Electrical, thermal and mechanical design and testing results are presented.

Decomposition and electro-physical model creation of the CREE 1200V, 50A 3-Ph SiC module

The CREE 1200V/50A, 25mΩ 6-Pack SiC MOSFET module (CCS050M12CM2) is decomposed into a full 3D CAD model, and materials identified, for use in electrical circuit and multi-physics simulations. A reverse engineering technique is first developed, outlined, and then demonstrated on the CREE module. The ANSYS Q3D Extractor is applied to the 3D CAD model where electrical, lumped parameter, parasitic circuit elements are determined. The model is also analyzed with a multi-physics simulator to provide in-situ thermal maps of the baseplate surface for application scenarios, e.g. with a thermal interface material and pin fin heat sink to capture the thermal spreading from junction to case. The complete model is made open source and freely distributed for use by the reader.

Novel Polymer Substrate-Based 1.2 kV/40: A Double-Sided Intelligent Power Module

Advanced power module packaging technology is currently being heavily investigated to take full advantage of Wide Band Gap (WBG) power semiconductor devices. As one of most widely applied power module technologies, intelligent power modules, typically for automotive industries, work well to achieve higher operating frequencies with lower losses by integrating gate driver circuits with power semiconductor devices. In this paper, a novel flexible polymer substrate-based intelligent power module is developed and characterized. By applying 80 µm-thick epoxy-resin based flexible dielectric as a substrate, the overall weight and volume of the power module is reduced, as well as the cost, compared with traditional direct bonded copper ceramic-based modules. The performance of the epoxy-resin based dielectric is investigated, and shows that the leakage current of the dielectric at >1.5 kV is less than 20 µA at 250 oC. Double-sided solderable 1.2 kV SiC MOSFETs and Schottky diodes are fabricated and applied in the module without bonding wires, significantly reducing the overall parasitic inductance to

Design methodology for a planarized high power density EV/HEV traction drive using SiC power modules

This paper provides a methodology for overall system level design of a high-power density inverter to be used for EV/HEV traction drive applications. The system design is guided to accommodate off-the-shelf SiC power modules in a planar architecture that ensures proper electrical, thermal, and mechanical performances. Bi-directional interleaved DC-DC boost structure and a three-phase voltage source inverter (VSI) have been utilized with the primary focus on the size, weight and loss reduction of passive components. A stacked layer approach has been used for a unique PCB-based busbar, ultra-low profile gate driver, and controller board. This holistic design approach results in a highly compact traction drive inverter with power density of 12.1 kW/L that has lower volume and weight compared to the commercially available state-of-the-art power converter systems.

The first demonstration of symmetric blocking SiC gate turn-off (GTO) thyristor

This paper reports the development of symmetric blocking SiC p-GTO thyristors. The proposed thyristor structure features a positive bevel edge termination implemented by orthogonal dicing technique. In this paper, a detailed design of the device structure, forward current-voltage characteristics, and symmetric blocking capabilities are discussed.

Design Considerations of Packaging a High Voltage Current Switch

In this paper an attempt has been made to demonstrate various package design considerations to accommodate series connection of high voltage Si-IGBT (6500V/25A die) and SiC-Diode (6500V/25A die). The effects of connecting the cathode of the series diode to the collector of the IGBT versus connecting the emitter of the IGBT to the anode of the series diode has been analyzed in regards to gate terminal operation and the parasitic line inductance of the structure. ANSYS Q3D/MAXWELL software have been used to analyze and extract parasitic inductance and capacitances in the package along with electromagnetic fields, electric potentials, and current density distributions throughout the package for variable parameters. SIMPLIS-SIMETRIX is used to simulate typical switch behavior for different parasitic parameters under hard switched conditions. Various simulation results have then been used to redesign and justify the optimized package structure for the final current switch design. The thermal behavior of such a package is also conducted in COMSOL in order to ensure that the thermal ratings of the power devices is not exceeded, and to understand where potentially harmful hotspots could arise and estimate the maximum attainable frequency of operation. The main motivation of this work is to enumerate detailed design considerations for packing a high voltage current switch package.Copyright

Feasibility of a MEMS Sensor for Gas Detection in HV Oil-Insulated Transformer

This paper addresses protection of oil-insulated transformers, using a microelectromechanical systems (MEMS) sensor system to augment or replace existing protection techniques. Traditional technologies used for protection and analysis involve pressure and temperature sensing, gas chromatography, and/or a Buchholz relay. The proposed MEMS device is immersed within the insulating fluid, e.g., oil, and primarily consists of multiple microscale turbines centrally shafted to a MEMS generator. The device utilizes relative differences in the velocity, pressure, and flow rate of fluid caused by electric faults. A differential electrical output is produced, which can be coupled to a remote recorder.

Design, Package, and Hardware Verification of a High-Voltage Current Switch

In this paper, an attempt has been made to demonstrate various package design considerations to accommodate series connection of high voltage Si-IGBT (6500V/25A die) and SiC-Diode (6500V/25A die). The effects of connecting the cathode of the series diode to the collector of the IGBT versus connecting the emitter of the IGBT to the anode of the series diode have been analyzed in regards to parasitic line inductance of the structure. Various simulation results have then been used to redesign and justify the optimized package structure for the final current switch design. The package is fabricated using the optimized parameters. A double pulse test-circuit has been assembled. Initial hardware results have been shown to verify functioning. The main motivation of this work is to enumerate detailed design considerations for packing a high voltage current switch package.

Development of an ultra-high density Power Chip on Bus (PCoB) module

A traditional power module uses metal clad ceramic (e.g. DBC or DBA) bonded to a baseplate that creates a highly thermally resistive path, and wire bond interconnect that introduces substantial inductance and limits thermal management to single-sided cooling. This paper introduces a Power Chip on Bus (PCoB) power module approach that reduces parasitic inductance through an integrated power interconnect structure. The PCoB maximizes thermal performance by direct attaching power chips to the busbar, integrating the heatsink and busbar as one, and uses a dielectric fluid, such as air, for electrical isolation. This new power module topology features all planar interconnects and double-sided air cooling. Performance evaluations are carried out through comprehensive electrical and multi-physics simulation and thermal testing for a 1200V, 100A rated single-switch PCoB design. Fabrication and assembly processes are included. For the developed double-sided air-cooled module, 0.5°C/w thermal resistance and 8nH power loop parasitic inductance are achieved.