Koji Shiozaki

A High-Density, High-Efficiency, Isolated On-Board Vehicle Battery Charger Utilizing Silicon Carbide Power Devices

This paper presents an isolated on-board vehicular battery charger that utilizes silicon carbide (SiC) power devices to achieve high density and high efficiency for application in electric vehicles (EVs) and plug-in hybrid EVs (PHEVs). The proposed level 2 charger has a two-stage architecture where the first stage is a bridgeless boost ac-dc converter and the second stage is a phase-shifted full-bridge isolated dc-dc converter. The operation of both topologies is presented and the specific advantages gained through the use of SiC power devices are discussed. The design of power stage components, the packaging of the multichip power module, and the system-level packaging is presented with a primary focus on system density and a secondary focus on system efficiency. In this work, a hardware prototype is developed and a peak system efficiency of 95% is measured while operating both power stages with a switching frequency of 200 kHz. A maximum output power of 6.1 kW results in a volumetric power density of 5.0 kW/L and a gravimetric power density of 3.8 kW/kg when considering the volume and mass of the system including a case.

Nickel–Tin Transient Liquid Phase Bonding Toward High-Temperature Operational Power Electronics in Electrified Vehicles

This paper presents the concept, fabrication, and evaluation for quality and reliability of nickel-tin transient liquid phase (Ni-Sn TLP) bonding that provides high reliability for high-temperature operational power electronics in electrified vehicles. The need for automotive power electronics to operate at high-temperature presents significant challenges in terms of packaging and bonding technology used. TLP bonding is one attachment approach that addresses these challenges and facilitates high remelting temperatures while allowing processing to occur at relatively low temperatures and pressures. In particular, the Ni-Sn TLP bonding process exhibits a number of desirable characteristics for power electronics, including popularity in conventional power electronics, low cost, and uniform and homogeneous alloy formation. The work herein presents Ni-Sn TLP bonding (ready for high-temperature operation) as applied to silicon power devices of relatively large size (12 mm × 9 mm). The quality and reliability of the developed bonding process was characterized using material, optical, and electrical analysis. Analysis indicates that the resulting bondline is uniformly composed of Ni3Sn4 alloy throughout the bond area. This bonding approach has exhibited excellent reliability for bonded devices after thermal cycling from -40°C to 200°C. Electrical properties of the bonded insulated gate bipolar transistor power devices demonstrated that Ni-Sn TLP bonding exhibits electrical performance comparable with conventional solder and is reliable at high-temperature operation.

Highly reliable nickel-tin transient liquid phase bonding technology for high temperature operational power electronics in electrified vehicles

This paper presents an approach to nickel-tin transient liquid phase (TLP) bonding that provides high reliability for high temperature operational power electronics in electrified vehicles. The need for automotive power electronics to operate at high temperature presents significant challenges in terms of the packaging and bonding technology used. Transient liquid phase (TLP) bonding is one attachment approach that addresses these challenges. The Ni/Sn TLP bonding process exhibits a number of desirable characteristics, including a good CTE match with silicon and silicon carbide, popularity in conventional power electronics, low cost, and uniform alloy formation. The work herein presents a Ni/Sn TLP bonding technology (ready for high temperature operation up to 200°C) as applied to large size silicon power devices (12 mm × 9 mm). Analysis indicates that the resulting bondline is uniformly composed of Ni3Sn4 alloy throughout. This bonding approach has exhibited excellent reliability for bonded devices after 1000 thermal cycles from -40 to 200°C.

Reliable and repeatable bonding technology for high temperature automotive power modules for electrified vehicles

This paper presents the feasibility of highly reliable and repeatable copper–tin transient liquid phase (Cu–Sn TLP) bonding as applied to die attachment in high temperature operational power modules. Electrified vehicles are attracting particular interest as eco-friendly vehicles, but their power modules are challenged because of increasing power densities which lead to high temperatures. Such high temperature operation addresses the importance of advanced bonding technology that is highly reliable (for high temperature operation) and repeatable (for fabrication of advanced structures). Cu–Sn TLP bonding is employed herein because of its high remelting temperature and desirable thermal and electrical conductivities. The bonding starts with a stack of Cu–Sn–Cu metal layers that eventually transforms to Cu–Sn alloys. As the alloys have melting temperatures (Cu3Sn: > 600 °C, Cu6Sn5: > 400 °C) significantly higher than the process temperature, the process can be repeated without damaging previously bonded layers. A Cu–Sn TLP bonding process was developed using thin Sn metal sheets inserted between copper layers on silicon die and direct bonded copper substrates, emulating the process used to construct automotive power modules. Bond quality is characterized using (1) proof-of-concept fabrication, (2) material identification using scanning electron microscopy and energy-dispersive x-ray spectroscopy analysis, and (3) optical analysis using optical microscopy and scanning acoustic microscope. The feasibility of multiple-sided Cu–Sn TLP bonding is demonstrated by the absence of bondline damage in multiple test samples fabricated with double- or four-sided bonding using the TLP bonding process.

A 16-element 77–81-GHz phased array for automotive radars with ±50° beam-scanning capabilities

This paper presents the first 16-element 77-81 GHz phased array receiver for automotive radars. The silicon phased array chip is packaged using very low-cost techniques, and is attached to a 16-element linear microstrip antenna array. The packaging is designed to result in <; -28 dB coupling between the channels even with wirebonds. The measured patterns show scanning to ±50o and agree well with simulations. The 16-element phased array receiver has been implemented with a transmitter and shows detailed images of targets and scenes in outdoor driving scenarios.

Double-sided nickel-tin transient liquid phase bonding for double-sided cooling

This paper presents double-sided nickel-tin transient liquid phase (Ni-Sn TLP) bonding technology and its application to double-sided cooling structures used in automotive power modules. Double-sided cooling is an emerging solution for heat dissipation problems inside compact power modules (used in electrified vehicles) and requires components providing highlevel reliability. This requirement is satisfied by Ni-Sn TLP bonding technology facilitating a high re-melting temperature reaching ~794 °C. Double-sided Ni-Sn TLP bonding is demonstrated using conventional power diodes having nickel layers on both sides. Electrical characterizations of the doubleside bonded diodes reveal consistent and reproducible bonding quality. In addition, excellent high temperature reliability of double-sided TLP bonding is exhibited by high temperature storage (at 300 °C) and thermal cycling (from -40 to 200 °C) evaluations. This presentation is the first time demonstration of double-sided TLP bonding using active power devices.

High current and high frequency planar inductor loss measurement and analysis

This paper presents an approach of a loss measurement and analysis for high current and high frequency planar inductor. The need for automotive power electronics to operate at high frequency is indispensable for compact packaging size. Accurate analysis of inductor loss is of great importance for downsizing power electronics systems. This paper introduces a loss analysis approach for high frequency and high current inductors, based on an LC resonant method. To demonstrate the accuracy of this method, a conventional calorimetric method was simultaneously conducted. A planar inductor loss-break-down is presented as a case study.

Highly Reliable Double-sided Bonding used in Double-sided Cooling for High Temperature Power Electronics

This paper demonstrates the feasibility of double-sided die attachment bonding, a key technology for double-sided cooling structures, using copper-tin transient liquid phase (Cu-Sn TLP) bonding. Recently, double-sided cooling has drawn particular interest by providing a notable improvement in thermal management and increasing allowable power density for automotive power electronics. The use of TLP bonding for double-sided attachment avoids a number of complications in the assembly process, enables multiple attachments, and provides a high bonding quality and reliability at high temperature operation (because of its high re-melting temperature). In addition, Cu-Sn TLP facilitates high thermal and electrical conductivities, which exactly correspond to the aim of double-sided cooling. Cu-Sn TLP bonding is developed using silicon dummy dies and DBC (direct bonded copper) substrates. The feasibility of double-sided Cu-Sn TLP bonding is demonstrated by (1) proof-of-concept fabrication, (2) optical analysis usin...