Operation Of Power Modules Research Articles

An Online Identification Method of Thermal Dissipation State for Forced Air-Cooled System of Power Converters

Thermal stress is the primary cause of malfunction and failure in power modules. As the main heat dissipation component, the heatsink plays a significant role in improving the reliability of power converters. However, due to the continuous accumulation of dust and impurities on the heatsink’s air inlet side, the thermal dissipation performance of the cooling system constantly declines, which influences the reliable operation of power modules. In this article, a computational fluid dynamics (CFD)-based simulation analyzes the declining mechanism of the heatsinks’ thermal transfer performance. Moreover, a novel online method is proposed for the cooling system’s thermal dissipation state identification. This method regards the steady-state thermal resistance as the feature parameter of the thermal dissipation state evaluation. And a parameter identification method is employed to identify the steady-state thermal resistance due to the difficulty of obtaining it in the transient thermal process. In addition, an ac/dc/ac pulsewidth modulation (PWM) converter is built for verification. The experimental results demonstrate that the proposed method enables accurate and fast identification of the cooling systems’ thermal dissipation state. It can be one of a solution for replacing the existing off-line manual periodic detection method, which helps improve detection efficiency and decrease maintenance costs.

Anisotropic highly conductive joints utilizing Cu-solder microcomposite structure for high-temperature electronics packaging

The miniaturization of power conversion systems requires high-power density operation of power modules, causing the heat-density increase. Therefore, it is essential to develop bonding technology to realize highly thermally conductive and reliable high-temperature joints. In this study, we propose a novel anisotropic microcomposite (AMC) joint that integrates a lotus-type porous Cu (LPC) sheet and Sn-based solder for high-temperature electronic applications. The AMC joint was successfully fabricated by infiltrating the molten solder into the unidirectional pores of the LPC sheet during a simple reflow process. Steady-state thermal conductivity measurements for a uniquely designed specimen revealed its equivalent thermal conductivity (142.4 W/m·K), 2.5 times higher than the solder. Finite element simulations supported its excellent thermal performance by investigating the heat flux distribution and thermal conductivity prediction that utilize a three-dimensional image-based constructed model. In addition, the aging test at 200 °C for 1008 h clarified a stable shear strength of over 46 MPa. This indicates a reliable mechanical performance at 200 °C, which is only 20 °C below the melting point of the solder. These experimental and numerical studies proved the potential of the novel joint as a high-temperature electronics joint and offered possible mechanisms for its thermal and mechanical property enhancement.

Electrical and Microstructural Reliability of Pressureless Silver-Sintered Joints on Silicon Carbide Power Modules Under Thermal Cycling and High-Temperature Storage

Low-temperature and pressureless silver (Ag) sintering was applied to a 1200 V/200 A silicon carbide (SiC) metal-oxide-semiconductor field-effect transistor (MOSFET) power module with a Ag-finished silicon nitride active metal-brazed substrate, and the results were evaluated for applicability in electric and hybrid electric vehicles. The sintering was performed at 220–240°C, 90 min in vacuum under nitrogen gas conditions; the bonding strength, bonding layer thickness (BLT), void content, and densification of the as-sintered Ag joints were 39 MPa, 71.4 µm, 2%, and 90.5%, respectively. The shear strength, BLT, densification, and microstructure of the Ag-sintered joints were compared before and after the thermal cycling test (− 50–150°C, 1100 cycles, TCT) and high temperature storage test (200°C, 1000 h, HTST). To simultaneously compare the electrical properties of the SiC power module with lead (Pb)-free solder joints, the same SiC MOSFET power module was manufactured using a Sn-3.0Ag-0.5Cu (SAC305) Pb-free solder. The shear strength and densification after TCT and HTST were 35.5 MPa and 39.7 MPa, as well as 92.8% and 94.8%, respectively. The on-resistance and total switching efficiency of the SiC power module with the Ag-sintered joint were also compared to those of the SAC305 solder joint module, which evinced maximum values of 7.3 mΩ and 10.7 mJ that were superior to those of 8.5 mΩ and 11.3 mJ for the SAC305 solder joint, respectively. Under the same measurement conditions, the maximum generated current and voltage values are lower than those of the solder joint module, so it is envisaged that stable power module operation is realizable for long-term use. The Ag-sintered joint surpassed the SAC305 solder interconnects in terms of the electrical and mechanical reliability of the power module. When a SiC wide band gap device was used, it was discovered that Ag sintering was superior to Pb-free solder interconnects to increase the power conversion efficiency of the power module.

Reliability of Cu Nanoparticles/Bi-Sn Solder Hybrid Bonding Under Cyclic Thermal Stresses

The influence of thermal cycle stress loading on hybrid bonding, which was formed by sintering a mixture of Cu nanoparticles and a eutectic Bi-Sn solder powder, has been investigated. A Si chip and a directly bonded aluminum (DBA) substrate were bonded using the hybrid bonding layer. The bonded sample was evaluated using a thermal cycle test (− 40°C and 250°C). The degradation process of the sample during the test was observed nondestructively using synchrotron radiation x-ray computed laminography. The thermal cycle stress loading had a minimal effect on the microstructure of the bonding layer, which has a high bonding strength owing to the liquid phase sintering and high decomposition melting temperature of the Cu-Sn compound formation. This property reduced the Al deformation of the DBA substrate caused by the thermal cycle loading, resulting in the suppression of the bonding layer degradation. Therefore, hybrid bonding can be instrumental in achieving the reliable operation of power modules at high temperatures.

СПОСОБИ МЕТАЛІЗАЦІЇ КЕРАМІКИ, ВИКОРИСТОВУВАНІ ПРИ ВИРОБНИЦТВІ СИЛОВИХ ЕЛЕКТРОННИХ МОДУЛІВ І ЕЛЕКТРОВАКУУМНИХ ПРИЛАДІВ

Power electronic modules are used in engineering related to the need to transmit high-current signals. Typical areas of application of such modules are aircraft navigation systems, elements of switching power circuits and other high-load connections. The central unit of the module is a ceramic base, on which conductive tracks are formed and electronic components are mounted. The finished substrate is often called a switchboard. The substrate performs two main functions: Is the dielectric basis of the printed circuit formed on one or two sides. Provides heat dissipation emitted by semiconductor crystals and circuit elements. Used for substrates non-hygroscopic ceramics, heat-resistant, is an insulating material with high mechanical and dielectric properties. It is relatively easy to manufacture and low cost. In the manufacture of power modules using ceramic substrates of aluminum oxide or nitride with a multilayer metallized coating with a thickness of several microns to several tens of microns (depending on the application), which provides the required degree of adhesion of the coating to ceramics and applied on one or both sides. The main requirements for the finished product are the minimum dimensions and low cost of materials and production process. In addition, the decisive factors are high technical characteristics, resistance to environmental influences and reliability. The design of the finished module must provide minimum values of transient thermal resistances, distributed inductances of power busbars, high insulation voltage. Adhesion strength depends on many factors: coating technology, film material, substrate material; and may decrease during operation of the finished product. During the operation of power modules, they are subjected to thermal and mechanical loads, including vibration. This leads to the destruction of components from overheating and damage to the mechanical damage of the modules. Often the failure occurs in the structure of the substrate-coating conductor. The main reason for this destruction is the low adhesive strength of the metal film to the ceramic base.

Review of Methodologies for Structural Integrity Evaluation of Power Modules

AbstractThis paper reviews the previous research on the methodologies for evaluating structural integrity of wire bonds and die-attachments in power modules. Under power module operation, these parts are subjected to repeated temperature variations which induce repeated thermal stress due to the mismatch in coefficients of thermal expansion (CTE) of the constituent materials. Thus, thermal fatigue phenomena are critical issues for the structural integrity of power modules. In the present paper, we also deal with the evaluation methodologies for thermal fatigue in the temperatures over 200 °C, which are expected operational temperatures for wide bandgap semiconductor power modules. The failure models based on the temperature range ΔT widely used in the power electronics community are critically reviewed from a mechanical engineering viewpoint. Detailed discussion is given concerning the superiority of failure models based on the physical quantities such as the inelastic strain range Δεin, the inelastic strain energy density range ΔWin, and the nonlinear fracture mechanics parameter range ΔT* over the conventional ΔT-based failure models. It is also pointed out that the distributed state concept (DSC) approaches based on the unified constitutive modeling and the unified mechanics theory are promising for evaluating the structural integrity of power modules. Two kinds of test methods, a power cycling test (PCT) and a thermal cycling test (TCT), are discussed in the relation to evaluating the lifetimes of wire-liftoff and die attach cracking.

Real-Time Monitoring of Thermal Response and Life-Time Varying Parameters in Power Modules

This article introduces new technologies for monitoring thermal response and life-time varying parameters of power electronic modules in real time without interrupting normal converter operation. The technologies are embedded in an adaptive thermal observer, which integrates temperature measurements and electrothermal models to estimate device losses and temperatures at reliability-critical locations of the power module. The observer structure includes a model reference adaptive system for adaptively calibrating device switching-loss models. This improves thermal monitoring accuracy, avoids time-consuming offline calibrations, and creates the opportunity for efficiency estimations during power module operation. The adaptive observer together with small-signal loss-excitation and system-identification technologies extract the thermal impedance of the power module in magnitude and phase over multiple frequency decades. This in situ thermal impedance spectroscopy has the unique feature of continuously providing information on the thermal interface of the power devices without interrupting normal inverter operation. The extracted information, i.e., life-time varying electrical and thermal parameters, enables diagnosing power module state-of-health with improved accuracy compared to prior technologies. It even allows separating different degradation effects, such as bond wire lift-off, device and base-plate solder delamination as well as deterioration of the convection process. With these new features, next generation monitoring systems can extract thermal response and degradation and thus protect power modules from severe thermal stress and overload. Furthermore, the obtained state-of-health information can be selectively used to reduce thermal stress and to schedule predictive maintenance leading to a safer and more reliable operation of future converter systems.

Material Characterization and Warpage Modeling for Power Devices Active Metal Brazed Substrates

The metallized insulating substrates work as mechanical supports for the circuitry of Power Module Packages. Due to their specific functions, substrates for power electronics are made by different materials. The conductive metal layers can assume different functions: the top metal serves as power circuitry routing while the bottom metal improves the mechanical robustness and thermal efficiency. Ceramic layer provides excellent electrical insulation. These features play an essential role in the operation of power modules, which are often operated at high voltage and high current density. The substrates, composed by materials with different thermal expansion coefficients, are subjected to cyclic stresses due to temperature variations induced by operative working conditions. The substrate layouts typically include differences in shape and/or thickness between the top and the bottom side; this generates asymmetrical distributions of stress/strain resulting in overall warpage. The variations of this warpage induce mechanical fatigue during lifetime and represent a limiting factor for reliability. The scope of the presented work is the characterization of the out of plane warpage of Active Metal Brazed substrates (AMB) by means of numerical approach. The elastoplastic properties of metal and ceramic have been measured, evaluating the thermal softening of the copper as well. These characteristics are needed to calculate AMB warpage through Finite Element Models (FEM), simulating the warpage induced by a passive temperature cycling. Warpage computed from numerical model have been benchmarked and validated with optical warpage measurements. The validated numerical model has been developed to optimize the substrate warpage variation during cycling improving the whole package reliability.

Experimentally validated methodology for real-time temperature cycle tracking in SiC power modules

The ability to monitor temperature variations during the actual operation of power modules is key to reliability investigations and the development of lifetime prediction strategies. This paper proposes an original solution, specifically devised with novel fast-switching silicon carbide (SiC) power MOSFETs in mind. The results show ability to track temperature variations resulting from active power cycling of the devices, including high speed transients, thus enabling to discriminate among different potential failure mechanisms. Validation of the proposed methodology and its accuracy is carried out with the support of infrared thermography.