Performance and testing of thermal interface materials

The increasing power and reduced die size of CPUs used in computers increases a need for significantly improved thermal interface materials (TIM). The TIM is used to reduce contact resistance at the CPU-heat sink interface. This work provides a state-of-the-art assessment on ‘thermal interface materials’, including fundamentals, materials used, their performance, and how interface resistance is measured. The performance of new commercial interface materials is given, as well as discussion of the advantages and disadvantages of different materials. The report notes that the recommended interface test method does not necessarily duplicate the installation and operating conditions in an actual computer installation. Recommendations are presented on the design and operation of an apparatus intended to simulate actual computer installation conditions. The innovative Penn State ‘low melting point alloy’ thermal interface material is described and compared to other commercial materials.     

Comparative evaluation of thermal interface materials for improving the thermal contact between an operating computer microprocessor and its heat sink

Testing of the relative effectiveness of various thermal interface materials for improving the thermal contact between the well-aligned mating surfaces of an operating computer microprocessor (with an integrated heat spreader) and its heat sink shows that carbon black paste, whether by itself or as a coating on aluminum or flexible graphite, is more effective than silver paste (Arctic Silver), but is comparable in effectiveness to aluminum paste (Shin-Etsu). The carbon black paste by itself is as effective as the Shin-Etsu paste coated aluminum. The Shin-Etsu paste is more effective than Arctic Silver, whether by itself or as a coating. The relative performance is mostly consistent with that assessed by measuring the thermal contact conductance. The correlation is particularly strong for conductance below 3×10⁴ W/m²·°C. The discrepancy is attributed to the difference in surface roughness between computer and guarded hot plate surfaces. In the case in which the mating surfaces of microprocessor and heat sink are not well aligned, Shin-Etsu and Arctic Silver are more effective than carbon black.     

A step forward in the transient thermal characterization of chips and packages

Generating compact dynamic thermal models is a key issue in the thermal characterization of packages. A further but related problem is the modeling of the thermal coupling between chip locations, for the use in electro-thermal circuit simulators. The paper presents a measurement based method which provides a way to solve both problems. A thermal benchmark chip has been designed and realized, to facilitate thermal transient measurements. The developed evaluation method provides the compact thermal multiport model of the IC chip including package effects, for the accurate electro-thermal simulation of the ICs. The evaluation method is also suitable to generate the compact thermal model of the package.     

Thermal characterization of high power LED with ceramic particles filled thermal paste for effective heat dissipation

The next generation packaging materials are expected to possess high heat dissipation capability. Understanding the needs for betterment in the field of thermal management, the present study aims at investigating the package level analysis on a high power LED. In this study, commercially available thermal paste was heavily filled with ceramic particles of aluminium nitride (AlN) and boron nitride (BN) in order to enhance the heat dissipation of the device. Different particle sizes of AlN and BN fillers were incorporated homogenously into the thermal paste and applied as a thermal interface material (TIM) for an effective system level analysis employing thermal transient measurement. It was found that AlN TIM achieve less LED junction temperature by a difference of 2.20 °C compared to BN filled TIM. Furthermore, among D₅₀ = 1170 nm, 813 nm and 758 nm, the AlN at D₅₀ = 1170 nm was found to exhibit the lowest junction temperature of 38.49 °C and the lowest total thermal resistance of 11.33 K/W compared to the other two fillers.     

Inline Rth control: Short time thermal transient evaluation for high power LEDs

As junction-to-case thermal resistance R_thJC is a primary performance and reliability parameter for high power light emitting diodes (LED) an accurate specification of this value is of paramount importance. Currently thermal transient characterization methods are reserved to research and quality laboratories. Especially the thermal calibration procedure requires an enormous effort of time. Therefore the R_thJC specification of a high volume production is based on a statistical approach. However, high test coverage or even a single unit test is desired. This paper presents a method for inline R_th control for high power LEDs. By skipping the conventional thermal calibration procedure the method compares the measured response of the device under test with a completely thermal characterized reference curve of a reference device. It enables to detect variations in thermal interface materials, e.g. failures in the thermal adhesive attach, with sufficient accuracy within some hundred milliseconds testing time. The achieved measurement results verify the applicability of inline R_th control in a high volume production.     

Study on thermal performance of high power LED employing aluminum filled epoxy composite as thermal interface material

This paper elucidates the thermal behavior of an LED employing metal filled polymer matrix as thermal interface material (TIM) for an enhanced heat dissipation characteristic. Highly thermal conductive aluminum (Al) particles were incorporated in bisphenol A diglycidylether (DGEBA) epoxy matrix to study the effect of filler to polymer ratio on the thermal performance of high power LEDs. The curing behavior of DGEBA was studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The dispersion nature of the Al fillers in polymer matrix was verified with Field Emission Scanning Electron Microscope (FESEM). The thermal performance of synthesized Al filled polymer composite as TIM was tested with an LED employing thermal transient measurement technique. Comparing the filler to polymer ratio, the rise in junction temperature for 60 wt% Al filled composite was higher by 11.1 °C than 50 wt% Al filled composite at cured state. Observed also from the structure function analysis that the total thermal resistance was 10.96 K/W higher for 60 wt% Al filled composite compared to 50 wt% Al filled composite. On the other hand, a significant rise of 9.5 °C in the junction temperature between cured and uncured samples of 50 wt% Al filled polymer TIM was observed and hence the importance of curing process of metal filled polymer composite for effective heat dissipation is discussed extensively in this work.     

Application of Green's functions for analysis of transient thermal states in electronic circuits

This paper presents an approach to the modelling of transient thermal states in electronic circuits using an analytical solution of the heat equation. Fully three-dimensional analytical time dependent solutions are determined with the help of Green's functions. The solution method is illustrated in detail on a practical example, where the results of transient thermal simulations of a real hybrid circuit are compared with infrared measurements.     

Evaluation of short pulse and short time thermal transient measurements

Thermal transient recording and the time constant spectrum analysis are widely used methods in the thermal testing and qualification of IC packages. A limitation of these methods is that recording of the complete transient response requires long time. This limitation, however, can be overcome by sophisticated procedures. The first method is to apply short power pulse for excitation; the second one is the interruption of the transients long before the thermal equilibrium is reached. The paper offers algorithms to evaluate these short pulse and short time measurements. The presented methods are suitable if the extraction of the little time constants is needed. This is the case if the transient method is used e.g. for die attach quality checking.     

Emulation-based transient thermal modeling of 2D/3D systems-on-chip with active cooling

State-of-the-art devices in the consumer electronics market are relying more and more on Multi-Processor Systems-On-Chip (MPSoCs) as an efficient solution to meet their multiple design constrains, such as low cost, low power consumption, high performance and short time-to-market. In fact, as technology scales down, logic density and power density increase, generating hot spots that seriously affect the MPSoC performance and can physically damage the final system behavior. Moreover, forthcoming three-dimensional (3D) MPSoCs can achieve higher system integration density, but the aforementioned thermal problems are seriously aggravated. Thus, new thermal exploration tools are needed to study the temperature variation effects inside 3D MPSoCs. In this paper, we present a novel approach for fast transient thermal modeling and analysis of 3D MPSoCs with active (liquid) cooling solutions, while capturing the hardware-software interaction. In order to preserve both accuracy and speed, we propose a close-loop framework that combines the use of Field Programmable Gate Arrays (FPGAs) to emulate the hardware components of 2D/3D MPSoC platforms with a highly optimized thermal simulator, which uses an RC-based linear thermal model to analyze the liquid flow. The proposed framework offers speed-ups of more than three orders of magnitude when compared to cycle-accurate 3D MPSoC thermal simulators. Thus, this approach enables MPSoC designers to validate different hardware- and software-based 3D thermal management policies in real-time, and while running real-life applications, including liquid cooling injection control.     

一种优化的微测热辐射计热学参数性能测试分析方法

优化的微测热辐射计热学参数的测试方法,与传统测试方法相比,能够实现热导和响应时间的精确测量,克服热学参数评估依赖仿真的缺陷,且该方法易于实现,工程应用性强.通过对研制的微测热辐射计性能进行相应的测试,确定了该测试方法准确、可靠.     

基于红外热像与电学测试法的OLED热学分析

采用红外 热成像与瞬态热学测试技术,测试并对比分析了有机电致发光二极管(OLED)的光电热学特性 。研究表明,OLED结温的升高会导致输入 电压的降低。在输入电流为100mA时,整个面板上呈现非 常明显的温度梯度,最高点与最低点 温差可高达30℃。在相同的工作条件下,采用红外热像测试获得的峰值温度比采用瞬态热 学测试获 得的温度要高,且温度梯度会随输入电流的大小发生变化。结合红外热像与电学测试法固有 特点的分析,指出两者的结合可以为OLED面板的热学设计与分析提供更具有指导意义的信息 。     

Evaluation of thermal transient characterization methodologies for high-power LED applications

In the past, thermal characterization methodologies for LED packages have mainly been derived from already existing solutions of the microelectronics industry. Within this paper, several issues regarding the determination of the junction-to-case thermal resistance R_thJC for LED packages are addressed. The new JESD51-14 standard is taken into consideration and especially the so called “point of separation” of the underlying dual-interface method is investigated. Experiments and finite element simulations were carried out in order to investigate the environmental influences on this crucial point. The investigations reveal that the point of separation changes depending on the thermal boundary condition at the case of the LED module, viz the quality of the package attach.     

Dynamic thermal modelling of a power integrated circuit with the application of structure functions

This paper presents dynamic thermal analyses of a power integrated circuit with a cooling assembly. The investigations are based on the examination of the cumulative and differential structure functions obtained from the circuit cooling curves recorded during transient circuit temperature measurements. The experiments carried out and the comprehensive study of the computed structure functions rendered possible determination of the interface contact resistance and the heat transfer coefficient values necessary for numerical thermal simulations illustrating the influence of these thermal model parameters on circuit temperature.     

一种二极管型红外热探测器热学参数的电学等效测 试方法

红外热探测器的热学参数包括热容、热导、热响应时间,反应了结构信息和器件性能。精确有效地获得这些参数,对探测器的结构优化与性能评估具有指导意义。二极管型红外热探测器是红外热探测器的主要类型之一。基于二极管型红外热探测器的自热效应,提出了一种热学参数的电学等效测试方法,具有测量精度高且实现简单的特点。并对自制的一款二极管型红外焦平面阵列像元进行了测试,测试结果与理论分析相符,验证了方法的可行性。     

自动化测试在业务支撑系统接口测试中的应用设计

为了提升测试效率,本文将自动化测试技术应用到业务支撑系统接口的测试。文中通过对接口测试的共性特点和自动化测试技术特点的分析,设计了基于用例和脚本模板化的接口自动化测试平台,给出了平台的功能框架、平台开展测试的核心流程、以及平台的3层实现架构。在对业务支撑系统的接口测试内容进行归类后,本文还给出了一些测试用例和测试脚本的模板,以对接口自动化测试平台设计作进一步的说明。     

Active control of boundary conditions for dynamic thermal characterization of electronic components

This paper presents a practical realization of the system for the active control of boundary conditions during the dynamic thermal characterization of electronic components. The control of boundary conditions is exercised by the dual cold plate cooling assembly equipped with Peltier thermo-electric modules and an appropriate control circuit. Additionally, a tensometer bridge is used to assure the parallel alignment of surfaces and to adjust the contact thermal resistance between particular layers. The operation of the entire control system is illustrated based on a practical example where Peltier module currents are adjusted in real time so as to impose isothermal or constant heat flux boundary conditions on a power diode package surface during measurements performed with time varying power dissipation in the device.     

印制电路板热油试验方法与评价

热应力试验是印制板生产中最常用的质量检验方法之一,文章通过热油试验方法的案例介绍,以指导检验人员正确掌握试验方法和质量评价技能。     

Influence of the metallic absorption layer on the quality of thermal conductivity measurements by the transient thermo-reflectance method

This work investigates numerically the influence of a metallic absorption layer on the laser-based measurements of the thermal conductivity of dielectric (SiO₂) and semiconductor (Si) electronic materials. The validity of the approach and the obtained results are assessed by comparison with experimental measurements obtained for gold-covered silicon dioxide samples. The results reveal the presence of behaviors associated with thermally thin and thermally thick absorption layers, depending on the ratio between the thickness of the absorption layer and the heat penetration depth. Optimal performance of the transient thermo-reflectance method was found to exist for thicknesses of metal layers falling between the identified thermally thin and thermally thick layers.