Thermal Impedance Measurement Research Articles

Exploring the process-microstructure-thermal properties relationship of resin-reinforced Ag sintering material for high-power applications via 3D FIB-SEM nanotomography

Resin-reinforced Ag sintering materials represent a promising solution for die-attach applications in high-power devices requiring enhanced reliability and heat dissipation. However, the presence of resin and intricate microstructure poses challenges to its thermal performance, and improvement strategies remain unclear. This work utilizes 3D FIB-SEM nanotomography to reconstruct the microstructure of this material under various process conditions. The analysis reveals that, even with an Ag volume fraction as low as 47.3%, Ag particles form a robust 3D network. Geometric tortuosity quantifies the effect of different sintering conditions on the Ag particle network in all spatial directions. Effective thermal conductivity is simulated based on realistic microstructure models. Results show a significant negative correlation between tortuosity and effective thermal conductivity. Increasing sintering temperature in Model B notably reduces tortuosity and enhances effective thermal conductivity. Sensitivity analysis underscores the dominant role of Ag volume fraction in regulating effective thermal conductivity. Finally, transient thermal impedance measurement of this material as a thin die-attach layer in actual high-power devices demonstrated its application potential. This article strives to explore the relationship between process, microstructure, and thermal properties of this material to provide a reference for further development.

Thermal Impedance Measurement of Thick-Film Resistor in High-Frequency Range Using Single-Detector IR System

This paper presents an innovative and simple method of high-frequency thermal impedance measurement using infrared (IR) technique. The method is based on the Fourier transformation of the input power signal and the thermal response of the object after supplying the heat source with square-wave current of different frequencies. The experiment was carried out using a single-detector, low-cost infrared system equipped with a photovoltaic detector module to measure the thermal impedance of an SMD thick-film resistor. Both the simulation using a compact thermal model and the measurement results are discussed.

Method to measure thermal impedance for all-active lasers using the athermalisation condition

Thermal impedance is an important material property which can be used in the design, optimisation and operation of semiconductor lasers. In this study, a new method is proposed for measurement of thermal impedance for all-active semiconductor lasers, using the athermalisation condition. This method is capable of measuring thermal impedance of several device sections at the same time for simple devices, while being capable of measuring the thermal impedance of the device as a whole for more complex structures. Three DBR devices of the same material properties were evaluated and the average impedance length product (Z th L) was determined to be 29.3±2.1 o C μm/mW and 39.33±2.8 o C μm/mW for the gain and grating sections respectively. Additionally, thermal impedance length product of the entire widely tunable Vernier device based on the same material was also determined to be 31.3±0.5 o C μm/mW.

Hydrothermal Synthesis of Nanocrystalline ZrO2-8Y2O3-xLn2O3 Powders (Ln = La, Gd, Nd, Sm): Crystalline Structure, Thermal and Dielectric Properties.

Zirconium dioxide (ZrO2) is one of the ceramic materials with high potential in many areas of modern technologies. ZrO2 doped with 8 wt.% (~4.5 mol%) Y2O3 is a commercial powder used for obtaining stabilized zirconia materials (8 wt.% YSZ) with high temperature resistance and good ionic conductivity. During recent years it was reported the co-doping with multiple rare earth elements has a significant influence on the thermal, mechanical and ionic conductivity of zirconia, due complex grain size segregation and enhanced oxygen vacancies mobility. Different methods have been proposed to synthesize these materials. Here, we present the hydrothermal synthesis of 8 wt.% (~4.5 mol%) YSZ co-doped with 4, 6 and 8 wt.% La2O3, Nd2O3, Sm2O3 and Gd2O3 respectively. The crystalline phases formed during their thermal treatment in a large temperature range were analyzed by X-ray diffraction. The evolution of phase composition vs. thermal treatment temperatures shows as a major trend the formation at temperatures >1000 °C of a cubic solid solutions enriched in the rare earth oxide used for co-doping as major phase. The first results on the thermal conductivities and impedance measurements on sintered pellets obtained from powders co-doped with 8 wt.% Y and 6% Ln (Ln = La, Nd, Sm and Gd) and the corresponding activation energies are presented and discussed. The lowest thermal conductivity was obtained for La co-doped 8 wt.% YSZ while the lowest activation energy for ionic conduction for Gd co-doped 8 wt.% YSZ materials.

Impact of SiC Switch–MOS for Thermal Impedance Evaluation of Power Module

In this paper, thermal impedances of Silicon carbide (SiC) power module assembled with a Schottky Barrier Diode (SBD)–wall–integrated trench MOSFET (SWITCH–MOS) and a conventional trench gate MOSFET (UMOS) are measured. Then they are compared to show the advantage of SWITCH–MOS for thermal impedance measurement. SiC power device is attracting attention as a candidate for future power device, since it can be operated at higher current density and higher switching speed than conventional silicon (Si) power device. The power module packaging technology for SiC power device should have low thermal impedance (both transient and steady state thermal resistance) to bring out a potential ability of the device. Thermal design often has difference from measurement due to various modeling errors such as power device heat generation, module structure, interfacial thermal resistance, and cooling environment. Therefore, accurate thermal impedance measurement is an essential technology. However, the thermal impedance measurement of SiC power modules has the significant issue due to the instability of the body diode built into the SiC–MOSFET. The thermal impedance is the junction temperature rise per heat generation amount of the device. The temperature dependence of the knee voltage of the body diode is used to measure the junction temperature of the MOSFET. Since the knee voltage of SiC–MOSFET changes depending on the gate voltage, a high negative gate bias was necessary to avoid this effect. However, the negative gate bias stress may cause serious device damage such as threshold shift. The SWITCH–MOS which has SBD built in near the MOSFET channel is expected to stabilize the junction temperature measurement and avoid the risk of device deterioration. Figure 1 shows the cross–sectional schematic of the SWITCH–MOS and the conventional UMOS. The SBD are formed on the trench sidewall in SWITCH-MOS, and the device structure is almost same to the UMOS. The temperature is detected by the PiN diode for the UMOS and by the SBD for the SWITCH–MOS. Both of them measure the temperature inside of the MOSFET cell. The appearance of the test module is shown in Fig. 2. Each type of the test module is composed of the SiC die (SWITCH–MOS, UMOS, and SBD), an SiN–AMC insulating circuit substrate and an Al baseplate. The components are attached each other using AuGe solder. The junction temperature is measured from the built–in voltage of the body diode in response to a constant current flowing from the source to the drain. In the case of the UMOS, the gate bias of −18 V is applied. The gate bias is zero for the SWITCH–MOS. The thermal impedance of each test module was measured by static mode (Fig. 3). Then, the thermal structure function was calculated by transient thermal analysis (Fig. 4). Both the thermal impedance and the structure function for the SWITCH–MOS and UMOS were in good agreement. Since the SWITCH–MOS does not need negative gate bias, the threshold shift issue does not occur in principle. In addition, it is possible to perform a transient thermal testing with a large current for a long time. Because the forward degradation does not occur even if a large current is applied to the SBD in the SWITCH–MOS. The SBD built into the SWITCH–MOS makes it easier and more accurate to measure the junction temperature of the SiC–MOSFET. The thermal impedance measurement using SWITCH-MOS not only allows the precise thermal modeling of SiC power modules to be performed, but also has the potential to be applied to the calibration of the thermal design and the evaluation of thermal properties inside of the package structure. Figure 1

Thermal Characterization of Silicon Carbide MOSFET Module Suitable for High-Temperature Computationally Efficient Thermal-Profile Prediction

This article characterizes the thermal behavior of a commercialized silicon carbide (SiC) power MOSFET module with special concerns on high-temperature operating conditions as well as particular focuses on SiC MOSFET dies. A temperature-dependent Cauer-type thermal model of the SiC MOSFET is proposed and extracted based on offline finite-element simulations. This Cauer model is able to reveal the temperature-dependent thermal property of each packaging layer, and it is suitable for the high-temperature thermal-profile prediction with sufficient computational efficiency. Due to the temperature-dependent thermal properties of the SiC die and ceramic material, the junction-heatsink thermal resistance can be increased by more than 10% under high-temperature conditions (up to 200 °C), which can considerably worsen thermal estimations of the SiC die and its packaging materials. Furthermore, the experimental measurement of transient thermal impedance was conducted under operating temperature variations (with virtual junction temperature ranging from 60.5 °C to 199.6 °C), and the effectiveness of the proposed temperature-dependent Cauer model was fully validated.

A Comparative Study of Silicon Carbide Merged PiN Schottky Diodes with Electrical-Thermal Coupled Considerations.

A comparative study of surge current reliability of 1200 V/5 A 4H-SiC (silicon carbide) MPS (Merged PiN Schottky) diodes with different technologies is presented. The influences of device designs in terms of electrical and thermal aspects on the forward conduction performance and surge current capability were studied. Device forward characteristics were simulated and measured. Standard single-pulse surge current tests and thermal impedance measurements were carried to show their surge capability and thermal design differences. An advanced thermal RC (thermal resistance-capacitance) model, with the consideration of current distribution non-uniformity effects, is proposed to accurately calculate the device junction temperature during surge events. It was found that a thinner substrate and a hexagonal layout design are beneficial to the improvement of the bipolar conduction performance in high current mode, as well as the surge current capability. The thinner substrate design also has advantages on thermal aspects, as it presents the lowest thermal resistance. The calculated failure temperature during the surge tests is consistent with the aluminum melting phenomenon, which is regarded as the failure mechanism. It was demonstrated that, for a SiC MPS diode, higher bipolar conduction performance is conducive to restraining the joule heat, and a lower thermal resistance design is able to accelerate the heat dissipation and limit the junction temperature during surge events. In this way, the MPS diode using a thinner substrate and advanced layout design technology is able to achieve 60% higher surge current density capability compared to the other technologies.

Comparative Thermal and Structural Characterization of Sintered Nano-Silver and High-Lead Solder Die Attachments During Power Cycling

13.5 mm × 13.5 mm sintered nano-silver attachments for power devices onto AlN substrates were prepared at 250 °C and a pressure of 10 MPa for 5 min and compared with Pb5Sn solder joint die attachments under constant current power cycling with an initial temperature swing of 50 °C-175 °C. Both effective thermal resistance and microstructural evolution of the samples were monitored using transient thermal impedance measurement and nondestructive X-ray computed tomography at regular power cycling intervals. The results showed a gradual increase in the effective thermal resistance of the Pb5Sn solder joints from 0.047 to 0.133 K/W from zero to 41k power cycles, followed by a rapid escalation to 0.5018 K/W at 52k cycles. This was accompanied with the formation and development of oblique cracks within the Pb5Sn die attachments until delamination occurred at the solder/device and solder/substrate interfaces. By contrast, the effective thermal resistance of the sintered Ag joints remained almost constant at 0.040 K/W up to 116k power cycles. This was explained in terms of thermally induced continuation of densification of the sintered structure and the formation and development of networked vertical cracks within the sintered Ag die attachments, some of which further extended into the Cu tracks of the AlN substrate.

Parameter driven monitoring for a flip-chip LED module under power cycling condition

In this paper, a parameter driven monitoring model is introduced, in which a flip-chip LED module was investigated during a power cycling test. This approach was investigated to develop a monitoring model to describe thermally induced solder fatigue as root cause of flip-chip failure in a power cycling test. As monitoring parameter the thermal resistance of the LED module was used, which was determined by thermal impedance measurements of the whole LED module, as well as for each LED chip itself. Further analyses of the occurring temperature at the LED junction recorded of each chip during the power cycling test were used to generate a prediction model. The evaluation of the temperature change allowed to forecast the number of cycles until failure.

Reliability and failure analysis of solder joints in flip chip LEDs via thermal impedance characterisation

Flip chip technology has made significant improvements to LED chip on board (COB) packages and modules by reducing thermal resistance compared with traditional wire bonded LEDs. However, one of the critical issues of flip chip packaged LEDs is the reliability of their solder interconnects, which are responsible for the heat transfer to the substrate. Based on a supply switching test, also called power cycle test, a model for monitoring and reliability was done to describe the remaining lifetime and additional the solder fatigue. Therefore, changes in thermal resistance of the LED-module were measured and correlated with solder fatigue of the LED flip chip package. Thermal impedance measurements were performed to monitor the status of the LED-module. Detailed analyses, comparing with the initial state, allow the evaluation of the occurring temperature swing of each LED chip. Single chip analysis combined with a thermal resistance driven monitoring model allows the calculation of remaining lifetime at each time during testing and beyond the first chip failure in a multi chip LED-module. Accordingly, it could be shown that the thermal impedance is a powerful tool for reliability monitoring and failure analysis.

Thermal impedance measurement of integrated inductors on bulk silicon substrate

The article presents the results of transient thermal measurements of a coil integrated in a silicon chip. Based on those measurements and using numerical procedures, thermal impedance, time constant distribution and structure functions were obtained. Next, using simple physical models of heat transfer phenomena, the 3 major time constants of the device under test were calculated, compared with measurement results and explained physically.

Channel temperature measurement in hermetic packaged GaN HEMTs power switch using fast static and transient thermal methods

A GaN-based power device is a superior component for high-frequency and high-efficiency applications and especially for applications that involve megahertz power conversion. In this work, a fast process of static thermal resistance (R th) and transient thermal impedance (Z th) measurements are made and analyzed to determine the thermal characteristics of the channel temperature of a hermetically packaged GaN power device. Five temperature-sensitive parameters (TSPs) are measured at temperatures from 20 to 160 °C. Measurements and statistical analyses included variations with temperature of on-resistance (R on), saturation drain current (I Dsat), drain conductance (g d), threshold voltage (V th), and knee voltage (V knee). The statistical analyses revealed the relationships between the heating curve parameter (R on) and the cooling curve parameters (V knee, I Dsat, g d, and V th). The average thermal resistance values are extracted as follows: Maximum R th is 2.99 °C W−1, minimum R th is 2.92 °C W−1, and the variation among the five TSPs is <3%. Conventional optical-based techniques such as infrared (IR) and micro-Raman thermography are destructive to packaged devices. Therefore, this study developed the two reliable and fast non-destructive methods for estimating channel temperature with the following features: (1) They elucidate static and transient characteristics; (2) they involve heating and cooling; and (3) they evaluate transient thermal impedance (TTI) and safe operating area (SOA). The heating curve method has advantages over cooling curve method in terms of capturing time (40 vs. 400 s, respectively), and a lower power excitation is required to obtain the transient channel temperature response.

Chalcogenide glass for AgI-based nanolayered films

Glass in the system GeSe2–Sb2Se3–AgI in monolith and film states has been investigated. Special attention has been paid to the crystallization stability and ionic conductivity of glass and films. The films were fabricated by the laser ablation of glass in a vacuum. The fabricated glass has been studied by the methods of X-ray diffraction and differential thermal analyses and impedance measurement. The sputtered films have been studied by X-ray diffraction and Raman spectroscopy in order to control their stability to crystallization and to compare their structure with that of monolith glass. It has been demonstrated that glass containing 40 mol % AgI is characterized with the softening point that is substantial for chalcogenide glass (190°C) and high crystallization stability, whereas the logarithm of their specific conductivity at 100°C is a value of the order of–3.5 at the activation energy of around 0.5 eV.

Apparatus for Measurement of Thermal Impedance of High-Power Light-Emitting Diodes and LED Assemblies

Measurement results of thermal impedance of powerful light-emitting diode assemblies are described. The measurements were performed with the help of a frequency method that involves heating the object under test by varying power harmonically. A pulse sequence of heating current, with the pulse length varying harmonically, is passed through the device under test. The p-n junction temperature is determined through measuring a temperature-sensitive parameter, which is forward voltage drop on the p-n junction between heating pulses at low measuring current. The first harmonic of the p-n junction temperature is determined by the discrete Fourier transform, which allows determination of thermal impedance module and phase at the modulation frequency of heating power. Analysis of the dependence of thermal impedance on modulation frequency allows determination of thermal impedance components corresponding to the structural elements of the object under test.

Numerical and Experimental Evaluation of the Microsecond Pulsed Heating Curve Technique Dedicated to Die Interconnection Characterization

This paper describes and qualifies a partial thermal impedance measurement technique to evaluate the thermal behavior of the physical layers close to the die in power electronic assemblies. The measurement approach is derived from the pulsed heating curve method; nonetheless, the experimental setup proposed here is fitted for a higher sensitivity analysis of die interconnections due to the extraction of the transient thermal impedance at very high current levels and short heating times. Another advantage of this method is that the cooling efficiency of the system has no impact on the sensitivity of the measurements, which makes it particularly suitable for aging monitoring or in-line manufacturing process control. The method is then implemented with power diodes in order to compare the thermal impedance of two power modules with different solder void repartitions. Experimental results and finite-element simulations show that this method has a very good sensitivity and can, therefore, be used to compare the quality of different die attaches without requiring an efficient power module cooling system.

Quantification of cracked area in thermal path of high-power multi-chip modules using transient thermal impedance measurement

Transient thermal impedance measurement is commonly used to characterize the dynamic behaviour of the heat flow path in power semiconductor packages. This can be used to derive a “structure function” which is a graphical representation of the internal structure of the thermal stack. Changes in the structure function can thus be used as a non-destructive testing tool for detecting and locating defects in the thermal path. This paper evaluates the use of the structure function for testing the integrity of the thermal path in high power multi-chip modules. A 1.2kV/200A IGBT module is subjected to power cycling with a constant current. The structure function is used to estimate the level of disruption at the interface between the substrate and the baseplate/case. Comparison with estimations of cracked area obtained by scanning acoustic microscopy (SAM) imaging shows excellent agreement, demonstrating that the structure function can be used as a quantitative tool for estimating the level of degradation. Metallurgical cross-sectioning confirms that the degradation is due to fatigue cracking of the substrate mount-down solder.

Thermal characterization system for transient thermal impedance measurement and power cycling of IGBT modules

This paper presents a custom-designed thermal characterization system for insulated-gate bipolar transistor (IGBT) modules. The main purpose of this system is to provide experimental capability for transient thermal impedance (Zth) measurement and power cycling reliability test on IGBT modules. LabVIEW programming was applied for circuit control and data acquisition. Gate-emitter voltage (Vge) of IGBT was used as the temperature-sensitive parameter for junction temperature (Tj) measurement. The linear relationship between Vge and Tj for IGBT can be measured by the system. Variation coefficient of lower than 0.5% was achieved for Zth measurement. IGBT modules with the same sample geometry but different die-attach processes were used for system verification: IGBT modules with nanosilver-sintered die-attach have on the average a 12% lower Zth than SAC305 soldered modules. The power cycling capability of the system was demonstrated by cycling a nanosilver-sintered IGBT module with Tj cycled between 45°C and 175°C. The cycling lifetime of the IGBT module was recorded as 48,000cycles with the failure criteria of 20% increase on Zth. Such lifetime is 50% longer than the predicted value from lifetime prediction model.

Characteristics and aging of PCB embedded power electronics

The decrease of battery prices makes the electrification of the power train an irresistible development. Also the introduction of a 48 V on-board grid is decided to supply large auxiliaries. For such applications cost is always an important factor.PCB embedded power electronics offers improvements compared to power electronics bonded and soldered on Al2O3 as dielectric material. These improvements are a reduction of height, lightweight construction, cost efficiency of the applied materials and a reduction of the parasitic inductance. Sinter layers offer an increase of the melting temperature from 220 to 935°C, compared to solder, and the thermal resistance between semiconductor and cooling water is low due to a thin dielectric layer of 150μm and the heat spreading inside the copper leadframe, together with PCB materials having a thermal conductivity of 1.5W/mK. A thermal resistance of 0.5K/W per IGBT can be achieved. This paper describes the challenges of the production process, the 5μm copper metallization of the semiconductor and the sinter process. Production failures were detected by curve tracer measurements, lock-in thermography and cross sections. The application potential of the embedding technology is demonstrated by measurements of the thermal impedance and temperature dependent partial discharge measurements. The effect of aging of PCB material by thermal cycling on the partial discharge behavior could be demonstrated. First results of an ongoing power cycling measurement are described as well. Finally the aspect of new PCB material without glass-fiber enforcement offering higher thermal conductivity and higher glass-transition-temperature is shown.

Electrical method to measure the transient thermal impedance of insulated gate bipolar transistor module

The thermal characterisation of insulated gate bipolar transistor (IGBT) module is very important, since the production consistency and reliability are affected when IGBT is exploited in high temperature. To investigate the transient thermal behaviour of IGBT, a transient thermal impedance (Z th) measurement system was built using the electrical method with gate-emitter voltage as temperature-sensitive parameter. Factors affecting the Z th measurement, such as environment temperature, heating power, duty cycle and heating time, were discussed in detail. The Z th of each component within IGBT module was measured by selecting right heating time before thermal equilibrium. It is found that the Z th measurement has high accuracy and repeatability, which is helpful to understand how thermal performance of IGBT module varies with architecture and material properties for power electronic packaging.

Sensorless Battery Internal Temperature Estimation Using a Kalman Filter With Impedance Measurement

This study presents a method of estimating battery cell core and surface temperature using a thermal model coupled with electrical impedance measurement, rather than using direct surface temperature measurements. This is advantageous over previous methods of estimating temperature from impedance, which only estimate the average internal temperature. The performance of the method is demonstrated experimentally on a 2.3 Ah lithium-ion iron phosphate cell fitted with surface and core thermocouples for validation. An extended Kalman filter, consisting of a reduced order thermal model coupled with current, voltage and impedance measurements, is shown to accurately predict core and surface temperatures for a current excitation profile based on a vehicle drive cycle. A dual extended Kalman filter (DEKF) based on the same thermal model and impedance measurement input is capable of estimating the convection coefficient at the cell surface when the latter is unknown. The performance of the DEKF using impedance as the measurement input is comparable to an equivalent dual Kalman filter using a conventional surface temperature sensor as measurement input.