Showing papers by "Khai D. T. Ngo published in 2010"

SiC Wirebond Multichip Phase-Leg Module Packaging Design and Testing for Harsh Environment

Abstract: In order to take full advantage of SiC, a high-temperature wirebond package for multichip phase-leg power module using SiC devices was designed, developed, fabricated, and tested. The details of the material comparison and selection are described, thus culminating a feasible solution for high-temperature operation. A thermal cycling test with large temperature excursion (from -55°C to 250°C) was carried out to evaluate the thermomechanical reliability of the package. During the test, the substrate failed before other parts in 20 cycles. A sealing edge approach was proposed to improve the thermal reliability of the substrate. With the strengthening of the sealing material, the substrate, die-attachment, and wirebond assemblies exhibited satisfactoriness in the thermomechanical reliability tests. In order to evaluate the high-temperature operation ability of designed package, one prototype module was designed and fabricated. The high-temperature continuous power test shows that the package presented in this paper can perform well at 250°C junction temperature.

A Novel High-Temperature Planar Package for SiC Multichip Phase-Leg Power Module

Abstract: This paper presents the design, development, and testing of a phase-leg power module packaged by a novel planar packaging technique for high-temperature (250°C) operation. The nanosilver paste is chosen as the die-attach material as well as playing the key functions of electrically connecting the devices' pads. The electrical characteristics of the SiC-based power semiconductors, SiC JFETs, and SiC Schottky diodes have been measured and compared before and after packaging. No significant changes (<;5%) are found in the characteristics of all the devices. Prototype module is fabricated and operated up to 400 V, 1.4 kW at junction temperature of 250°C in the continuous power test. Thermomechanical robustness has also been investigated by passive thermal cycling of the module from -55°C to 250°C. Electrical and mechanical performances of the packaged module are characterized and considered to be reliable for at least 200 cycles.

New core loss measurement method for high frequency magnetic materials

Abstract: Magnetic core loss is an emerging concern for integrated POL converters. As switching frequency increases, core loss is comparable to or even higher than winding loss. Accurate measurement of core loss is important for magnetic design and converter loss estimation. And exploring new high frequency magnetic materials need a reliable method to evaluate their losses. However, conventional method is limited to low frequency due to sensitivity to phase discrepancy. In this paper, a new method is proposed for high frequency (1MHz∼50MHz) core loss measurement. The new method reduces the phase induced error from over 100% to <5%. So with the proposed methods, the core loss can be accurately measured.

Characterization of lead-free solder and sintered nano-silver die-attach layers using thermal impedance

Abstract: Since a die-attach layer has significant impact on the thermal performance of a power module [1], its quality can be characterized using thermal performance. In this paper, a measurement system for thermal impedance is developed to evaluate three die-attach materials. Thanks to its high temperature sensitivity (10mV/0C), the gate-emitter voltage of an IGBT is used as the temperature-sensitive parameter. The power dissipation in the IGBT is maintained constant regardless of the junction temperature by a feedback loop. Experimental results show that the sample using sintered nano-silver for die-attach has 12.1% lower thermal impedance than the samples using SAC305 and SN100C solders. To check the degradation of the die-attachment, three samples using three die-attach materials were thermally cycled from -400C to 1250C. The experimental results show that after 500 cycles, the thermal impedance of SAC305 samples and SN100C samples is increased by 12.8% and 15% respectively, which is much higher than the sample using nano-silver paste for die-attach (increased by 4.1%).

Technology road map for high frequency integrated DC-DC converter

Abstract: This preliminary road map is provided for state-of-the-art technologies and trends toward integration of point-of-load converters. This paper encompasses an extended survey of literature ranging from device technologies and magnetic materials to integration technologies and approaches. The paper is organized into three main sections. 1) Device technologies, including the trench MOSFET, lateral MOSFET and lateral trench MOSFET, are discussed along with their intended applications. The critical role of device packaging to high-frequency integration is assessed. 2) Magnetic materials: In recent years, a number of new magnetic materials have been explored in various research labs to facilitate magnetic integration for high-frequency POL applications. These data are collected and organized to help selecting magnetic material for various current levels and frequency ranges. 3) Levels of integration, which are defined with the focus on magnetic integration techniques and approaches, namely board-level, package-level and wafer-level, each with suitable current scale and frequency range.

Characterization of encapsulants for high-voltage, high-temperature power electronic packaging

Abstract: Seven encapsulants with operating temperature up to 250°C have been surveyed for possible use in high-temperature, high-power planar packages. Processability was assessed by studying the flow fronts and the cured properties of the surveyed materials between paralleled plates. Two encapsulants did not pass the flow test, and another two did not pass the curing test. Material E, F, and G were confirmed to be comparably stable with respect to temperature, and both dielectric strength and dielectric permittivity decreased around 40% and 30%, respectively, as the temperature increased from 25°C to 250°C. The thermal aging test showed that materials were hardened during the aging process, and cracking started in the material matrix. The dielectric strength of the sample would significantly drop to only around 10 kV/mm once cracking occurred.

Thermal fatigue behaviour of Al2O3-DBC substrates under high temperature cyclic loading

Abstract: Purpose – The purpose of this paper is to study the phenomenology of Al2O3‐DBC substrate thermal‐cracking under different high temperature cyclic loadings. The extremely low cycle fatigue (ELCF) life prediction model for ductile materials was used to describe the thermal fatigue life of Al2O3‐DBC substrates.Design/methodology/approach – Four groups of thermal cycling tests using Al2O3‐DBC substrates with 0.65 mm thick copper were conducted using different peak temperatures. The failure samples were observed by optical microscope. The thermal plastic strain distribution in the Al2O3‐DBC substrates was analyzed using a finite element method with the Chaboche model for describing plastic deformation of copper. The ELCF life prediction model was used to predict the life of Al2O3‐DBC substrates under high temperature cyclic loadings.Findings – Interface cracking was observed to initiate at the short edge of the bonded copper and deviated into the ceramic layer when the crack grew beyond the critical length of ...

Parametric Study of Joint Height for a Medium-Voltage Planar Package

Abstract: Due to the thin structure used in planar packaging, the electric field intensity within the encapsulation is high, leading to degradation of the dielectric performance. To resolve this issue, a metal posts interconnected parallel plate structure (MPIPPS) is used to reduce the high electric field concentration in the power module. However, the high bonding joint in MPIPPS causes large thermo-mechanical stress within the solder layers. This paper proposes a methodology to optimize the joint height based on a trade-off between the thermo-mechanical performance and dielectric performance of the power module. The impact of the joint height on thermo-mechanical stress and dielectric performance of the module is investigated quantitatively using ANSYS and Maxwell simulations. The results show that using a 0.4 mm joint height and Nusil R-2188 encapsulation, the power module can achieve 3 kV breakdown voltage. Experimental results agree with the simulation results.

High-density system integration for medium power applications

Abstract: Over the past ten years, there has been increased incorporation of electronic power processing into alternative, sustainable, and distributed energy sources, as well as energy storage systems, cars, airplanes, ships, homes, data centers, and the power grid. The goals have been to reduce the size, weight, and maintenance and operational costs of these power systems, while increasing overall energy efficiency, safety, and reliability. This paper summarizes some of the authors' research efforts in the last four years on the improvements in power density and physical integration of power converters, mostly for vehicular applications. Several approaches to integration of active components into high-temperature modules are presented together with examples of the evaluation and modeling of 1.2 kV SiC JFET and MOSFET. Possible improvements in the power density through hybrid passive and active integration of an EMI filter and of an energy storage capacitor in single-phase PWM rectifier are also shown. Examples of converter integration for a 10 kW motor drive with active front-end using SiC devices operating at 250 °C, and for paralleling three-phase boost rectifiers with interleaved PWM are presented.

High Temperature SiC Power Module Electrical Evaluation Procedure

Abstract: To take full advantage of silicon carbide semiconductor devices, high-temperature device packaging needs to be developed. This paper describes potential defects from design and fabrication procedures, and presents a systematic electrical evaluation process to detect such defects. This systematic testing procedure can rapidly detect many defects and reduce the risk in high-temperature packaging testing. A multichip module development procedure that uses this testing procedure is also presented and demonstrated with an example.

A novel integrated power inductor in silicon substrate for ultra-compact power supplies

Abstract: A novel silicon-based inductor, power inductor in silicon, or PIiS, has been proposed and experimentally demonstrated. The PIiS is fabricated at wafer level using a silicon molding micromachining technique, in which 200 µm thick copper windings are embedded into a silicon substrate and both sides of the substrate are capped with a polymer-magnetic power composite. Through-silicon vias (TSVs) and copper routings are also added so that a PIiS can be directly used as a surface mountable packaging substrate. A 3×3×0.6 mm3 PIiS with a measured inductance of 390 nH has been fabricated. The Q factor of this PIiS is 10 at 6 MHz. An ultra compact buck converter has been made by surface mounting off-shelf power ICs and capacitors on a PIiS. The buck converter is 3×3×1.2 mm3, which has successfully delivered 500 mA at 1.8V with an 80% efficiency at 6 MHz.

An improved design for transmission line busbar EMI filter

Abstract: The transmission line busbar filter is a good choice for a high-density EMI containment solution. This paper presents a study of the application of a transmission-line busbar filter in a motor drive system. To examine the potential improvement for busbar filters, low-frequency attenuation and basic modeling of busbar filters in a motor drive are studied. Based on the knowledge gained from the modeling, an improved busbar filter is proposed and fabricated. Experimental results show a significant improvement on busbar filter attenuation.

Automatic layout design for power module

Abstract: The layout of power modules is one of the key points in power module design, especially for high power densities, where couplings are increased. In this paper, along with the design example, an automatic design processes by using genetic algorithm are presented. Some practical considerations and implementations are introduced in the optimization of the layout design of the module.

Innovative liquid cooling configurations for high heat flux applications

Abstract: Breakthroughs in the recent cutting-edge technologies have become increasingly dependent on the ability to safely dissipate large amount of heat from small areas. Improvements in cooling techniques are therefore required to avoid unacceptable temperature rise and at the same time maintain a high efficiency. Jet impingement is one such cooling scheme which has been widely used to dissipate transient and steady concentrated heat loads. But with constantly increasing cooling needs, conventional jet impingement cooling is no longer a viable option. Considerable improvements are therefore required to meets such stringent requirements. A combination of swirl-impingement-fin generating geometry is one such alternative. Even without a fin, an overall enhancement of 150% – 200% in the maximum heat transfer coefficient has been recorded both experimentally and computationally due to impingement and associated swirl. Moreover, the presence of fins further increases the cooling area. The present scheme is therefore expected to overcome the existing heat distribution and cooling problems in high heat flux dissipating devices.

Novel PCM and Jet Impingement Based Cooling Scheme for High Density Transient Heat Loads

Abstract: Breakthroughs in the recent cutting-edge technologies have become increasingly dependent on the ability to safely dissipate large amount of heat from small areas. Improvements in cooling techniques are therefore required to avoid unacceptable temperature rise and at the same time maintain high efficiency. Jet impingement is one such cooling scheme which has been widely used to dissipate transient and steady concentrated heat loads. With constantly increasing transient cooling needs, conventional pin-fin cooling and conventional jet impingement cooling are not meeting the requirements. Considerable improvements are therefore required to meet such stringent requirements without any significant changes in the cooling system. A combined cooling scheme based on jet impingement and phase change materials (PCMs) is presented as one such alternative to existing cooling systems. A high heat storage capability of PCMs in combination with a high heat transfer rates from impingement cooling can help overcome the existing heat distribution and transient cooling problems in high heat flux dissipating devices. Preliminary conjugate CFD simulations show promising results. Additionally, experimental validation of the simulation predictions has also been performed. A reasonably good agreement was found between the predictions and experiments.Copyright © 2010 by ASME