Direct Bonded Copper Research Articles

Numerical characterizations of the thermomechanical response of power modules with ceramic substrates and lead-free bonds

PurposeThe present paper aims to study the influence of the substrate system on the thermomechanical response of various lead-free die attach materials used in power electronics using nonlinear finite element simulations.Design/methodology/approachParticularly, three ceramic substrate systems, including direct copper bonded (DCB) and aluminum nitride (AlN) – as well as silicon nitride (Si3N4) –based insulated metal substrate (IMS) configurations are examined in this study. Additionally, three die attach systems, namely, silver-tin transient liquid phase (TLP), sintered silver (Ag) and sintered copper (Cu) are included in the analysis. ANSYS software is employed to build the finite element models of the power modules and to conduct the nonlinear thermomechanical investigations.FindingsThe simulation results revealed that the IMS, Si3N4 and DCB-based power modules end up with significantly lower interconnect inelastic strains and inelastic strain energies suggesting better fatigue life performance. Additionally, the bonding layer stresses and expected failure mechanism are not influenced by the substrate configuration rather than the bond material. For instance, the silver-tin TLP joints develop high stresses and hence brittle failures are expected. Nonetheless, the sintered Ag and sintered Cu have significantly lower stresses which could lead to fatigue-induced failures.Originality/valuePower electronics use various ceramic-based substrate systems because of their improved thermal conductivity, electrical insulation and heat resistance properties. The proper selection of the substrate structure could highly enhance the thermal fatigue of the power modules. Markedly, the findings of this research are useful for designing highly reliable and effective power modules continuously subjected to thermomechanical loadings.

Cold Gas Spraying Copper Metal On AlN Ceramics as an Alternative to Thick DBC Substrates for Power Electronics

Abstract This study investigates the use of cold gas spraying (CGS) as a low-temperature additive manufacturing method to bond copper onto aluminum nitride (AlN) substrates for electronic packaging of high-power applications. While direct bond copper (DBC) technique is commonly used, it has limitations due to the large mismatch in coefficient of thermal expansion, which affects substrate reliability. This work employed cold gas spraying (CGS) to mechanically bond Cu on AlN. The study explores the effect of multiple sprays, spray angle and spraying direction on deposition thickness, coating surface roughness, and deposited volume through a factorial design of experiments (DOE). The results, based on optical and scanning electron microscopy combined with profilometry data, showed that coatings sprayed at a 60° angle had a smoother profile topography and less surface roughness than those sprayed at a 90° angle. After depositing 10 layers, a surface roughness (Sa) of around 30 µm and a coating thickness of over 300 µm were successfully attained. These findings provide valuable insights into the processing factors affecting the growth and quality of copper coatings on AlN substrates via multiple sprays, thus enabling the realization of CGS technology as a potential solution to DBC substrates for electronic packaging of wide-bandgap semiconductors.

Interface regulation of micro-sized sintered Ag-10Al composite based on in-situ surface modification and enhanced microstructure stability in power electronic packaging

The increasing demand for high-power SiC semiconductors necessitate the development of a die attachment material that combines high-temperature resistance, reliability, and cost-effectiveness. In this study, a novel micro-sized composite, Ag-10Al paste, containing 10 wt% Al particles, was designed. A remarkable phenomenon, the ejection of ultrafine Ag nanoparticles from micron-sized Ag flakes, was observed for the first time. The phenomenon was utilized for the in-situ surface modification of Al. Subsequently, the microstructure and mechanical properties of the sintered Ag-10Al/direct bonded copper (DBC) joints were studied. Results indicated that the Ag-10Al composite exhibited superior microstructure stability compared to sintered Ag. The Ag/Al interface was systematically analyzed, revealing a unique Ag/nano Ag2O/Al2O3 amorphous/Al structure. This structure was formed through the Ag nanoparticle jetting effect of Ag flakes, achieving effective bonding between nano Ag2O and Al2O3 amorphous phases through mutual dissolution at the atomic level. Moreover, the sintered Ag-10Al joint demonstrated enhanced mechanical performance stability over the sintered Ag joint. After 1000 h aging at 300 ℃, the shear strength of the sintered Ag-10Al joint reached 34.1 MPa, meeting the requirements for power semiconductor packaging. In conclusion, the Ag-10Al composite paste was thoughtfully designed, excelling in both performance and cost-effectiveness.

Online learning for DBC segmentation of new IGBT samples based on computed laminography imaging

Insulated gate bipolar transistor (IGBT) is a power semiconductor module .Voids may arise in its solder process when a contaminant or gas is absorbed into the solder joint. They heavily influence the heat exchange efficiency of IGBT, so void inspection is very important. The segmentation of solder region is a crucial step for automated defect detection of IGBT based on x-ray computed laminography (CL) system. In recent years, deep learning has made remarkable process in semantic segmentation and has been used for the segmentation of solder joint between the direct bonded copper (DBC) substrate and baseplate, which has been proved to be accurate and efficient. However, deep learning architectures exhibit a critical drop of performance due to catastrophic forgetting when new IGBT samples encountered. Hence, this paper proposes to use online learning techniques to continuously improve the learned model by feeding new IGBT samples without losing previously learned knowledge.

Concepts for realizing High-Voltage Power Modules by Embedding of SiC Semiconductors

Today’s power electronics modules typically consist of a ceramics substrate (DBC – Direct Bond Copper), carrying IGBTs, diodes or MOSFETs. These semiconductors are soldered or sintered to the ceramics and their top sides are interconnected by thick Al wires. An integration of further components or functions on the DBC substrate is difficult or even not possible. Therefore, driver circuits and controllers have to be mounted to a separate substrate, typically an organic Printed Circuit board (PCB). The PCB has to be connected to the DBC by wires or pins. The mechanical integration of the whole system requires a bulky housing. Embedding of power semiconductors like SiC MOSFET allows a significant size reduction, improved electrical performance and a high degree of reliability of such modules. In the last years, the capability of PCB embedding technology for the realization of low and high voltage power modules was demonstrated. Fraunhofer IZM together with partners from the industry demonstrated the feasibility for different applications, from single die SiC packages to high voltage automotive traction inverters. In this paper, a general overview about innovative power module technologies will be given and the embedding of power semiconductors will be introduced in detail. It will address all most relevant point, like the demands on the semiconductor, the thermal and electrical considerations as well as the demands on the used materials. To address the integration of the required driver circuits and controllers, the idea of modularization such electronics systems will also be presented. Here already packaged components will be used and embedded into PCB layers too. As a result, a modular approach to form a complete system will be developed. Different functional layers, e.g. power switches, logic modules, will be formed and finally stacked und connected to form the system. The concept and first realized demonstrators will be discussed.

Improvement of Bonding Strength and Thermal Shock Reliability for Ag Sinter Joining Direct on Al Substrate

Ag sinter paste joining as a proven die bonding technology have been used in the electric vehicle. However, for the Ag sinter paste joining, metallization layers on substrate are usually necessary such as Ni-P/Au or Ni-P/Ag to get a good bonding quality. The direct bonding on DBC (direct bonded copper) or DBA (Direct Bonded Aluminum) substrates without metallization layers are very attractive. In this study, we investigated the direct bonding on an aluminum (Al) substrate by Ag sinter paste and propose an abrasive blasting processes to treat the Al surface to increase the initial bonding quality. The result show that the shear strength of SiC/Al joint structure by Ag sinter paste can be improved by treating the Al surface. The shear strength of joint structure without surface treatment increased from 26.9 MPa to 32.2 MPa for a strong blasting treatment on Al surface. In addition, the results of thermal shock test (-40 ℃~150℃) also show that the blasting treatment on Al surface can improve the shear strength and reliability of SiC/Al joint structure.

Automotive Silicon Carbide Power Module Cooling With a Novel Modular Manifold and Embedded Heat Sink

Abstract The next generation of integrated power electronics packages will implement wide-bandgap devices with ultrahigh device heat fluxes. Although jet impingement has received attention for power electronics thermal management, it is not used in commercial electric vehicles (EVs) because of the associated pressure drop and reliability concerns. In this paper, we present a modular thermal management system designed for automotive power electronics. The system achieves superior thermal performance to benchmarked EVs while adhering to reliability standards and with low pumping power. The system utilizes a low-cost and lightweight plastic manifold to generate jets over an optimized heat sink, which is embedded in the direct-bonded-copper (DBC) substrate. The embedded heat sink concept leverages additive manufacturing to add elliptical pin fins to the DBC substrate. The heat sink geometry is optimized for submerged jet impingement using a unit-cell model and an exhaustive search algorithm. The model predictions are validated using unit-cell experiments. A full-scale power module model is then used to compare the DBC-embedded heat sink against direct DBC cooling and baseplate-integrated heat sinks for single-sided (SS) and double-sided (DS) cooling concepts. Using the SS and DS DBC-embedded cooling concepts, the models predict a thermal resistance that represents a reduction of 75% and 85% compared to the 2015 BMW i3, respectively, for the same water-ethylene glycol inverter flowrate. We have shown that an inverter with a 100-kilo-Watt-per-liter power density is achievable with the proposed design.

Effects of High Humidity and High Salt Spray Environments on Surface Properties of Direct Bonding Copper

Effects of High Humidity and High Salt Spray Environments on Surface Properties of Direct Bonding Copper

Optimizing New Power Switch Technology

Power switches are critical components in power conversion for a wide variety of applications, including DC-AC inverters for electric vehicles (EVs), solid state breakers, and energy storage devices. Improving the efficiency and performance of semiconductor power switch components can have wide benefits, improving the efficiency and accelerating deployment of these applications. Compared to conventional power switches, such as insulated-gate bipolar transistors (IGBTs), the B-TRAN™ bidirectional power switch from Ideal Power offers significant improvements in efficiency, reducing power losses by 50% or more depending on the application. With its higher efficiency, B-TRAN results in less heat being generated and thus has significantly lower thermal management requirements. In addition, a single B-TRAN™ replaces multiple conventional power switches for bidirectional applications. Beginning in mid-2020, Ideal Power teamed with QP Technologies, a leading provider of microelectronic packaging and assembly services, to package their B-TRAN switches in various TO packages (a wide range of small-pin-count packages often used for discrete parts such as transistors or diodes). The development work started with TO-247, then moved TO-264 packages, and finally transitioned to a custom direct-bond copper (DBC) solution. To achieve a high-reliability design, QP Technologies and Ideal Power focused on developing die and packaging designs based on flip-chip technology in lieu of wirebonding to maximize the life cycle of the product. This paper investigates the challenges, solutions and finally the fabrication of the first double-sided B-TRAN device.

Heat Dissipation Design of High-Power Wide-Bandgap Power Module with Insulated Metal Substrate

In general, power modules are manufactured as direct bonding copper (DBC) substrates to withstand high temperatures and high power. The DBC substrate has a sandwich structure in which copper layers are formed on upper and lower parts and ceramic is formed as an insulating layer therebetween. Ceramic has excellent insulation properties but is difficult to process and is vulnerable to mechanical stress due to a difference in coefficient of thermal expansion (CTE) between copper. In this regard, research on the development of power modules using various materials is being conducted. In this paper, an insulating metal substrate (IMS) was designed and analyzed using a dielectric film as an insulating layer. IMS substrates are easier to process than ceramics and have a higher CTE, so they are more resistant to mechanical stress than DBC substrates. In addition, it may be made very thin through easy processing, thereby overcoming low thermal conductivity compared to ceramic. In this paper, IMS substrates of various thicknesses were designed based on the easy processability of the dielectric film, and simulations were performed to compare heat dissipation characteristics with Al2O3-based DBC substrates.

Location dependent down-rating of voids in high power solder connections for automotive power modules

The development of cost-effective, void- and lead-free high-power die attach for automotive power modules has been a major challenge for the last decades. Particularly voids at the die attach have the potential of reducing the lifetime of the interconnection between the die and the direct copper bonded (DCB) substrate demonstrably, caused by overheating of the die [1]. This study evaluates a method to determine the influence of the void position and size on the local thermal resistance of the solder interconnection. The formular of the local thermal resistance generated by using FEM simulation shows, that the permitted local maximum void size depends on the position of the void. The defined correlation factor reduces the individual void areas according to their position and thus the permitted thermal resistance is not exceeded.

Point-Contact Bonding of Integrated Three-Dimensional Manifold Microchannel Cooling Within Direct Bonded Copper Platform

Abstract A microchannel heat sink integrated with a three-dimensional manifold using direct bonded copper (DBC) is promising for high power density electronics due to the combination of low thermal resistance and reduced pressure drop. However, this requires much progress on the fabrication and high-quality point-contact bonding processes of the microchannel substrate and three-dimensional manifold DBCs. In this study, we have developed processing techniques for surface preparations and high-quality point-contact solder bonding between the two DBC substrates. We utilized chemical polishing followed by electroless plating to prevent excess solder from blocking the microchannels. We performed a parametric study to investigate the impact of bonding time and surface roughness on the tensile strength of the bonding interface. The bonding strength increased from 1.8 MPa to 2.3 MPa as the bonding time increased from 10 to 30 min while reducing the surface roughness from Rz = 0.21 to 0.05 μm, resulting in increasing the bonding strength from 0.16 MPa to 2.07 MPa. We successfully tested the microcooler up to the inlet pressure of 70 kPa and pressure drop of 30 kPa, which translates to the tensile strength at the bonding point contacts, which remains well below the 2.30 MPa. We achieved the junction-to-coolant thermal resistance of 0.2 cm2 K/W at chip heat flux of 590 W/cm2. Thus, our study provides an important proof-of-concept demonstration toward enabling high power density modules for power conversion applications.

High Performance SiC Power Module Based on Repackaging of Discrete SiC Devices

Increased adoption of electric vehicles (EV), photovoltaic (PV), and battery energy storage systems (BESS) is driving the need for high-current SiC power modules. The state-of-the-art multichip module is substantially more expensive than the IGBT module. This paper proposes a cost-effective packaging methodology for high-power SiC intelligent power modules (IPMs) with discrete SiC devices. The proposed IPM integrates the gate drivers, decoupling capacitors, snubbers, discrete SiC devices, direct bond copper (DBC), base plate, temperature sensors, and overcurrent protection circuits, achieving very low loop inductance and thermal resistance, and more than 50% cost reduction. A 1200V/480A/2.15mΩ half-bridge IPM is presented for comparison with commercial counterparts. A 1200V/240A/4.3mΩ six-phase IPM is developed, and its performance is experimentally verified.

Inductive Sintering of Silver Micro Particles for Bonding of Microelectronic Components

In this article, an efficient die-bonding technology based on silver sintering due to induction heating is presented. By using this technology, the heat for the sintering reaction is locally limited to the bonding area and heating of the entire power module is avoided. Furthermore, the sintering reaction is promoted due to current flow between the silver particles, and the sintering time is drastically reduced. Next to the experimental trials presented in this paper, finite element (FE) simulation methods were applied to develop a suitable induction coil geometry for the bonding of a diode to a direct bonded copper (DBC) substrate. Additional heating and sintering tests verified the reliability of the simulation model as well as the technological approach. Diodes were successfully bonded during the experiments and were analyzed by means of scanning electron microscopy (SEM) and function tests to qualify the inductive bonding technology. The results presented in this paper demonstrate that induction heating has high potential for cost-effective production in the field of die attach and can drastically increase the output in power-electronics production.

Моделирование теплоэлектрических процессов в силовых модулях на MOSFET-транзисторах

The paper represents thermal model of power MOSFET module based on a transistors mounted on copper-ceramic DBC (Direct Bond Copper) plate. The analysis of thermal processes in the module caused by pulse heating of particular transistors was performed by the finite elements method using COMSOL Multiphysics. The model performs estimation of the temperature field on the DBC plate and transistors overheat temperature. The modeling results was compared to the experiment – thermal impedance matrix measured by the modulation method using the heating power modulated by the harmonic law. Analysis of the data obtained allows to conclude that the calculated and experimental values of the dies overheating temperature are in good agreement with each other and confirms the correctness of the developed thermal power module model

A direct bonding copper degradation monitoring method for insulated gate bipolar transistor modules: Boundary‐dependent thermal network combined with feedback control

AbstractThe direct bonding copper (DBC) substrates of insulated gate bipolar transistor (IGBT) modules degrade inevitably under cycling thermo‐mechanical stress, causing potential threat to the reliability of IGBT modules. However, little attention has been paid to monitoring their degradation. This paper proposes a DBC degradation monitoring method for IGBT modules, which combines boundary‐dependent thermal network and feedback control. A thermal network is employed to describe the internal material degradation of IGBT modules and can be extracted from a finite‐element method model. The boundary conditions including power losses and DBC degradation are considered, enabling the thermal network suitable for various working conditions and different DBC degradation conditions of IGBT modules. The DBC degradation is characterised by its equivalent thermal conductivities measured in the thermal cycling ageing experiments. On the basis of the boundary‐dependent thermal network, feedback control is applied to monitor DBC degradation by regulating boundary‐dependent thermal impedances. Finally, the proposed model is verified from the effectiveness and accuracy of DBC degradation monitoring and junction temperature calculation. This method casts new light on thermal network modelling and could provide a feasible method for the monitoring of DBC degradation.

Multi-Level Embedded Three-Dimensional Manifold Microchannel Heat Sink of Aluminum Nitride Direct Bonded Copper for the High-Power Electronic Module

Abstract Better thermal management is a key enabler of higher power density in traction inverter power modules. For the first time, we successfully fabricated and tested a microchannel with a three-dimensional (3D) manifold cooler (MMC) using aluminum nitride (AlN)-based directed bonded copper (DBC) substrates. The microchannels (width ∼300 μm and height ∼450 μm) and 3D manifold fluidic passages (width ∼300 μm and height ∼600 μm) were fabricated in two DBC substrates using the femtosecond laser and subsequently bonded using transition liquid phase (TLP) bonding. In this study, the hydraulic and thermal performance of the 3D MMC is measured and validated with numerical simulation. The proposed 3D MMC is capable of removing heat at 600 W/cm2 with a 10 kPa pressured drop at the thermal thermal resistance of 0.2 cm2 K/W. The optimized designs via geometric and layout rearrangement were conducted, which indicates the pressure drop can be further reduced by 10× while maintaining the same thermal performance.

Interfacial Diffusion Mechanism between ALD Al2O3 passivation/Cu in Direct Bonded Copper Substrate for Power Electronics

Direct bonded copper(DBC) substrate requires surface treatments for oxidation prevention and adhesion enhancement to die-attachment. Conventional surface treatment, electroless nickel immersion gold (ENIG) has a cost and environmental problems, and immersion silver is sensitive to temperature and humidity. To solve these problems, this study presents the invention of aluminum oxide (Al2O3) passivation for DBC Cu pads, which meets the requirements of oxidation prevention and adhesion enhancement to die-attachment. Ultrathin Al2O3 passivation layers (~20nm) by atomic layer deposition(ALD) were coated on DBC Cu pads for replacing conventional ENIG and immersion silver surface finishes. This paper presents bondability and interfacial diffusion mechanism between ALD Al2O3 passivation/Cu in DBC substrate.

Design to cost Ag free silicon nitride AMB substrate for automotive power module applications

Silver free AMB technology addresses the cost-performance gap between the active metal brazed (AMB) Si3N4 based metal ceramic substrates (MCS) suitable for automotive applications and the cost-efficient direct copper bonded (DCB) Al2O3 substrates suitable for applications with lower requirements. The cost-reduction of the condura®.ultra process is achieved by using a silver free brazing technology combined with an efficient brazing process. Within this report we will demonstrate the thermal cycling capability, the peel strength of the condura®.ultra process combined with a design to cost Si3N4 ceramic substrate. Additionally showing results regarding isolation partial discharge of performance and robustness in thermal resistance measurements.

Single-Phase Jet Impingement Cooling for a Power-Dense Silicon Carbide Power Module

The adoption of silicon carbide (SiC) devices in the electric vehicle (EV) industry is increasing due to their superior performance over silicon devices. SiC devices enable further miniaturization of EV inverters, increasing their power density, which results in thermal management challenges. In this paper, the limits of single-phase jet impingement cooling are explored for an automotive SiC power module. We propose embedding pin fins in the direct-bonded-copper (DBC) substrate of the power module package using laser powder bed fusion additive manufacturing. The thermalhydraulic performance of the DBC-embedded pin fins is compared against folded fins that are directly soldered to the DBC substrate. A heat conduction analysis was conducted on a SiC package to determine the target heat transfer coefficient (HTC) for the heat sink. A water-ethylene glycol (WEG) jet impingement on the proposed concepts was studied using unit-cell models to achieve the target HTC. The studied designs put emphasis on the reliability and manufacturability requirements of the automotive industry. The thermal performance of DBC-embedded pin fins outperformed the DBC-soldered folded fins. The performance of the DBC-embedded pin fins is benchmarked against WEG-based cooling systems of commercial EVs. With the proposed cooling solution, we have shown a pathway of reducing the specific thermal resistance by 75% compared to BMW i3 thermal management system without any penalty on pressure drop or parasitic power.