Practices of IC package reliability testing are reviewed briefly, and the application of transient thermal analysis is examined in great depth. For the design of light sources based on light emitting diode （LED） eff...Practices of IC package reliability testing are reviewed briefly, and the application of transient thermal analysis is examined in great depth. For the design of light sources based on light emitting diode （LED） efficient and accurate reliability testing is required to realize the potential lifetimes of 105 h. Transient thermal analysis is a standard method to determine the transient thermal impedance of semiconductor devices, e.g. power electronics and LEDs. The temperature of the semiconductor junctions is assessed by time-resolved measurement of their forward voltage （Vf）. The thermal path in the IC package is resolved by the transient technique in the time domain. This enables analyzing the structural integrity of the semiconductor package. However, to evaluate thermal resistance, one must also measure the dissipated energy of the device （i.e., the thermal load） and the k-factor. This is time consuming, and measurement errors reduce the accuracy. To overcome these limitations, an innovative approach, the relative thermal resistance method, was developed to reduce the measurement effort, increase accuracy and enable automatic data evaluation. This new way of evaluating data simplifies the thermal transient analysis by eliminating measurement of the k-factor and thermal load, i.e. measurement of the lumen flux for LEDs, by normalizing the transient Vf data. This is especially advantageous for reliability testing where changes in the thermal path, like cracks and delaminations, can be determined without measuring the k-factor and thermal load. Different failure modes can be separated in the time domain. The sensitivity of the method is demonstrated by its application to high- power white InGaN LEDs. For detailed analysis and identification of the failure mode of the LED packages, the transient signals are simulated by time-resolved finite element （FE） simulations. Using the new approach, the transient thermal analysis is enhanced to a powerful tool for reliability investigation of semiconductor packages in accelerated lifetime tests and for inline inspection. This enables automatic data analysis of the transient thermal data required for processing a large amount of data in production and reliability testing. Based on the method, the integrity of LED packages can be tested by inline, outgoing inspection and the lifetime prediction of the products is improved.展开更多
Lithium-ion batteries'safe and effective functioning depends on reliable and precise heat control.In this study,we explore the thermal behaviour of a 48-V,30-Ah LiCoO_(2)battery pack utilising an unconventional tr...Lithium-ion batteries'safe and effective functioning depends on reliable and precise heat control.In this study,we explore the thermal behaviour of a 48-V,30-Ah LiCoO_(2)battery pack utilising an unconventional transient thermal analysis technique with a simplified constant heat-generating formula based on the Bernardi equation.This work assessed the effect of several discharge rates and heat transfer coefficients on thermal performance by modelling temperature distribution and heat dissipation inside the battery pack.Heat transfer coefficients 5 W/(m^(2)·K)for natural air convection,10 W/(m^(2)·K)for forced convection of air and discharge rates0.5C,1C,1.5C and 2C on thermal performance were investigated using a sensitivity analysis.The results show that forced convection improves temperature distribution and considerably enhances heat dissipation at a discharge rate of 0.5C.However,the study reveals that advanced thermal management techniques are especially vital.Even forced air convection finds it difficult to maintain temperatures within the optimal range at higher discharge rates,thus emphasizing the need to optimise cooling conditions to guarantee thermal stability and prevent hotspots.The findings underline and offer insightful analysis of the relative impact of discharge rates and cooling conditions on lithium-ion battery pack thermal behaviour.展开更多
This paper proposes a transient thermal analysis model for a nitrogen-cooled cryogenic system used in superconducting electromagnetic suspension magnets.First,the structural parameters of the nitrogen cryogenic system...This paper proposes a transient thermal analysis model for a nitrogen-cooled cryogenic system used in superconducting electromagnetic suspension magnets.First,the structural parameters of the nitrogen cryogenic system and the internal hightemperature superconducting magnet are detailed.Subsequently,temperature change simulations during the system's cooling process using a cryocooler,as well as during the cooling and nitrogen-insulation process,were conducted using COMSOL software.Finally,simulations of the temperature variations during the system's offline operation were performed.This study provides valuable references for the design and optimization of nitrogen-cooled cryogenic systems.展开更多
Boron-doped aluminum nitride （B-AlN） thin films were synthesized on Al substrates by using chemical vapor deposition method by changing the synthesis parameters and were used as thermal interface material for high p...Boron-doped aluminum nitride （B-AlN） thin films were synthesized on Al substrates by using chemical vapor deposition method by changing the synthesis parameters and were used as thermal interface material for high power light emitting diode （LED）. The B-AlN thin film-coated Al substrate was used as heat sink and studied the performance of high power LED at various driving currents. The recorded transient cooling curve was evaluated to study the rise in junction temperature （Tj）, total thermal resistance （gth_tot） and the substrate thermal resistance （Rth_sub） of the given LED. From the results, the B-AlN thin film （prepared at process 4） interfaced LED showed low Rth-tot and Tj value for all driving currents and observed high difference in Rth_tot （△Rth_tot =2.2 K/W） at 700 mA when compared with the Rth-tot of LED attached on bare Al substrates （LED/Al）. The Tj of LED was reduced considerably and observed 4.7 ℃ as ATj for the film prepared using process 4 condition when compared with LED/Al boundary condition at 700 mA. The optical performance of LED was also tested for all boundary conditions and showed improved lux values for the given LED at 700 mA where B-AlN thin film was synthesized using optimized flow of Al, B and N sources with minimized B and N content. The other optical parameters such as color correlated temperature and color rendering index were also measured and observed low difference for all boundary conditions. The observed results are suggested to use B-AlN thin film as efficient solid thin film thermal interface materials in high power LED.展开更多
The authors have developed a large-signal simulation technique extending an in-house small-signal simulation code for analyzing a 94 GHz double-drift region impact avalanche transit time device based on silicon with a...The authors have developed a large-signal simulation technique extending an in-house small-signal simulation code for analyzing a 94 GHz double-drift region impact avalanche transit time device based on silicon with a non-sinusoidal voltage excitation and studied the effect of junction temperature between 300 and 550 K on the large-signal characteristics of the device for both continuous wave （CW） and pulsed modes of operation. Results show that the large-signal RF power output of the device in both CW and pulsed modes increases with the increase of voltage modulation factor up to 60%, but decreases sharply with further increase of voltage modulation factor for a particular junction temperature; while the same parameter increases with the increase of junction temperature for a particular voltage modulation factor. Heat sinks made of copper and type-IIA diamond are designed to carry out the steady-state and transient thermal analysis of the device operating in CW and pulsed modes respectively. Authors have adopted Olson＇s method to carry out the transient analysis of the device, which clearly establishes the superiority of type-IIA diamond over copper as the heat sink material of the device from the standpoint of the undesirable effect of frequency chirping due to thermal transients in the pulsed mode.展开更多
文摘Practices of IC package reliability testing are reviewed briefly, and the application of transient thermal analysis is examined in great depth. For the design of light sources based on light emitting diode （LED） efficient and accurate reliability testing is required to realize the potential lifetimes of 105 h. Transient thermal analysis is a standard method to determine the transient thermal impedance of semiconductor devices, e.g. power electronics and LEDs. The temperature of the semiconductor junctions is assessed by time-resolved measurement of their forward voltage （Vf）. The thermal path in the IC package is resolved by the transient technique in the time domain. This enables analyzing the structural integrity of the semiconductor package. However, to evaluate thermal resistance, one must also measure the dissipated energy of the device （i.e., the thermal load） and the k-factor. This is time consuming, and measurement errors reduce the accuracy. To overcome these limitations, an innovative approach, the relative thermal resistance method, was developed to reduce the measurement effort, increase accuracy and enable automatic data evaluation. This new way of evaluating data simplifies the thermal transient analysis by eliminating measurement of the k-factor and thermal load, i.e. measurement of the lumen flux for LEDs, by normalizing the transient Vf data. This is especially advantageous for reliability testing where changes in the thermal path, like cracks and delaminations, can be determined without measuring the k-factor and thermal load. Different failure modes can be separated in the time domain. The sensitivity of the method is demonstrated by its application to high- power white InGaN LEDs. For detailed analysis and identification of the failure mode of the LED packages, the transient signals are simulated by time-resolved finite element （FE） simulations. Using the new approach, the transient thermal analysis is enhanced to a powerful tool for reliability investigation of semiconductor packages in accelerated lifetime tests and for inline inspection. This enables automatic data analysis of the transient thermal data required for processing a large amount of data in production and reliability testing. Based on the method, the integrity of LED packages can be tested by inline, outgoing inspection and the lifetime prediction of the products is improved.
文摘Lithium-ion batteries'safe and effective functioning depends on reliable and precise heat control.In this study,we explore the thermal behaviour of a 48-V,30-Ah LiCoO_(2)battery pack utilising an unconventional transient thermal analysis technique with a simplified constant heat-generating formula based on the Bernardi equation.This work assessed the effect of several discharge rates and heat transfer coefficients on thermal performance by modelling temperature distribution and heat dissipation inside the battery pack.Heat transfer coefficients 5 W/(m^(2)·K)for natural air convection,10 W/(m^(2)·K)for forced convection of air and discharge rates0.5C,1C,1.5C and 2C on thermal performance were investigated using a sensitivity analysis.The results show that forced convection improves temperature distribution and considerably enhances heat dissipation at a discharge rate of 0.5C.However,the study reveals that advanced thermal management techniques are especially vital.Even forced air convection finds it difficult to maintain temperatures within the optimal range at higher discharge rates,thus emphasizing the need to optimise cooling conditions to guarantee thermal stability and prevent hotspots.The findings underline and offer insightful analysis of the relative impact of discharge rates and cooling conditions on lithium-ion battery pack thermal behaviour.
文摘This paper proposes a transient thermal analysis model for a nitrogen-cooled cryogenic system used in superconducting electromagnetic suspension magnets.First,the structural parameters of the nitrogen cryogenic system and the internal hightemperature superconducting magnet are detailed.Subsequently,temperature change simulations during the system's cooling process using a cryocooler,as well as during the cooling and nitrogen-insulation process,were conducted using COMSOL software.Finally,simulations of the temperature variations during the system's offline operation were performed.This study provides valuable references for the design and optimization of nitrogen-cooled cryogenic systems.
基金financially supported by Collaborative Research in Engineering, Science and Technology (CREST) under Grant No. 304/PFIZIK/650601/C121
文摘Boron-doped aluminum nitride （B-AlN） thin films were synthesized on Al substrates by using chemical vapor deposition method by changing the synthesis parameters and were used as thermal interface material for high power light emitting diode （LED）. The B-AlN thin film-coated Al substrate was used as heat sink and studied the performance of high power LED at various driving currents. The recorded transient cooling curve was evaluated to study the rise in junction temperature （Tj）, total thermal resistance （gth_tot） and the substrate thermal resistance （Rth_sub） of the given LED. From the results, the B-AlN thin film （prepared at process 4） interfaced LED showed low Rth-tot and Tj value for all driving currents and observed high difference in Rth_tot （△Rth_tot =2.2 K/W） at 700 mA when compared with the Rth-tot of LED attached on bare Al substrates （LED/Al）. The Tj of LED was reduced considerably and observed 4.7 ℃ as ATj for the film prepared using process 4 condition when compared with LED/Al boundary condition at 700 mA. The optical performance of LED was also tested for all boundary conditions and showed improved lux values for the given LED at 700 mA where B-AlN thin film was synthesized using optimized flow of Al, B and N sources with minimized B and N content. The other optical parameters such as color correlated temperature and color rendering index were also measured and observed low difference for all boundary conditions. The observed results are suggested to use B-AlN thin film as efficient solid thin film thermal interface materials in high power LED.
文摘The authors have developed a large-signal simulation technique extending an in-house small-signal simulation code for analyzing a 94 GHz double-drift region impact avalanche transit time device based on silicon with a non-sinusoidal voltage excitation and studied the effect of junction temperature between 300 and 550 K on the large-signal characteristics of the device for both continuous wave （CW） and pulsed modes of operation. Results show that the large-signal RF power output of the device in both CW and pulsed modes increases with the increase of voltage modulation factor up to 60%, but decreases sharply with further increase of voltage modulation factor for a particular junction temperature; while the same parameter increases with the increase of junction temperature for a particular voltage modulation factor. Heat sinks made of copper and type-IIA diamond are designed to carry out the steady-state and transient thermal analysis of the device operating in CW and pulsed modes respectively. Authors have adopted Olson＇s method to carry out the transient analysis of the device, which clearly establishes the superiority of type-IIA diamond over copper as the heat sink material of the device from the standpoint of the undesirable effect of frequency chirping due to thermal transients in the pulsed mode.
