Thermal Interface Materials Thickness Research Articles

Effect of lead-free solder thermal interface material thickness on the reliability of electronic components in a random vibration environment

The reliability of electronic components has persistently posed challenges for engineers. This study addresses the critical need of understanding the impact of random vibration on the reliability of lead-free solder as thermal interface materials (TIM) within electronic components. ANSYS software was deployed to design, develop, and simulate the electronic model, with a focus on the TIM. SAC405 lead-free solder served as the TIM, its thickness was varied between 0.01 to 0.06 mm (at 0.01 mm intervals). The results from this investigation reveal relevant correlations. As the TIM thickness increases, there's a noticeable reduction in stress and strain while the deformation increases. Remarkably, a direct relationship emerges between TIM thickness and fatigue life; thicker TIM correlates with increased fatigue life. In addition, at a TIM thickness of 0.01 mm, the fatigue life measurements were 2.76 x 104, 1.63 x 104, and 0.792 x 104 for Equations 1, 2, and 3, respectively. These findings carry profound implications for engineers, serving as a guiding framework to aid in the selection of optimal TIM thickness for electronic components if lead-free solders are used as TIM. Understanding these trade-offs between stress, strain, deformation, and fatigue life is pivotal, empowering engineers to make informed decisions during electronic system design and development, ultimately enhancing overall reliability. Using lead-free solders as TIM in electronic applications is proposed by this study due to the thermal and reliability benefits presented.

Impact of thermal interface material on power cycling lifetime of IGBT module

In the DC power cycling test of standard IGBT power modules, cooling conditions include but are not limited to the coolants' type, temperature and flow rate as well as the type and thickness of thermal interface materials (TIM). The cooling conditions may have an impact on the entire process of the test. At present, few papers report this aspect. In this paper, different kinds and thickness of the TIM are used to change the cooling conditions, which are quantitatively characterized by the cooling time (toff). The impact of the TIM on power cycling lifetime of IGBT module is studied. The results show that when the toff becomes longer, the power cycling lifetime of IGBT module will improve. A thermal-mechanical co-simulation is carried out to further study the failure mechanism behind for the IGBT under different cooling conditions.

Optimisation of a microelectronic assembly package using response surface methodology

This article addressed heat conduction in microelectronics applications. ANSYS finite element design software was used to design the model, while Design Expert software was used for the response surface methodology (RSM) analysis. The components analysed were heat-sink base (HSB) thickness, thermal interface material (TIM) thickness, and chip thickness. A design of experiment comprising of 15 central composite design (CCD) for the coded levels (low (-) and high (+)) of the factors were generated. Heat flow was applied to the chip while a convective coefficient was applied to the heat-sink. The temperature solution was used to calculate the thermal resistance response for the 15 CCD experimental runs. The results from the RSM study proposed an optimal (minimization analysis) combination of 3.5 mm, 0.04 mm, and 0.75 mm, for HSB thickness, TIM thickness, and chip thickness respectively. While the optimal mean thermal resistance of 0.31052 K/W was achieved from the proposed optimal parameters.
 Keywords: RSM; CCD; thermal resistance; temperature; microelectronics

Optimal Lid Design Parameters for Reducing Warpage of Flip-chip Package

Abstract Flip-chip packages are usually integrated with a stiffener ring (SR) or lid to reduce the warpage which usually consumes considerable substrate space and hence, reduce the effective area available for placement of dies and passive components. With chip module size growing in modern semiconductor devices (e.g., to enable heterogeneous integration of different functional dies), there is a need to reduce the substrate area occupied by the lid while also reducing the package warpage to an allowable value. This requires an accurate understanding of how different parameters of the lid affect the warpage of the package. Here, for a large package, effects of the lid design variables, including (i) SR versus lid, (ii) lid foot width, (iii) lid plate thickness to foot width ratio, (iv) lid material, and (v) thickness of thermal interface material (TIM) connecting the die and the lid, on the warpage have been analyzed using the 3-D elasticity theory and the finite element method. It is found that for a given value of the lid plate thickness to foot width ratio, the warpage of the package is a non-monotonic function of the foot width and is not necessarily minimum for the maximum value of the foot width. The effects of lid material and TIM thickness are found to depend upon the foot width. Various results presented here should provide packaging engineers with guidelines to obtain optimal lid designs that minimize the package warpage while offering noticeable saving in the effective substrate area.

Improvement in the heat dissipation of matrix LED headlamps for vehicles according to the thickness and thermal conductivity of thermal interface materials

This study examined the effects of thermal interface materials (TIMs) in light-emitting diode (LED) headlamps for vehicles based on thermally conductive plastics. Heat transfer is a very important issue in LED applications because the stability and performance of LEDs decrease considerably with increasing junction temperature. When two solid surfaces are placed in contact, a TIM is used to reduce the thermal interface resistance. This study examined the effects of the thickness (0.3, 0.5, and 1.0 mm) and thermal conductivity (1.8, 3.0, 5.0, and 11.0 W m−1 K−1) of a TIM on the soldering temperature (TS). TS increased with increasing TIM thickness. In addition, TS decreased with increasing thermal conductivity of the TIM. The junction temperature (TJ) was lower than the others when a TIM with a high thermal conductivity of 11 W m−1 K−1 was used. Overall, the TJ and TS can be reduced using a suitable high thermal conductivity TIM with an appropriate thickness.

Mechanical Characterization of Thermal Interface Materials and Its Challenges

Thermal interface materials (TIMs) play a vital role in the performance of electronic packages by enabling improved heat dissipation. These materials typically have high thermal conductivity and are designed to offer a lower thermal resistance path for efficient heat transfer. For some semiconductor components, thermal solutions are attached directly to the bare silicon die using TIM materials, while other components use an integrated heat spreader (IHS) attached on top of the die(s) and the thermal solution attached on top of the IHS. For cases with an IHS, two TIM materials are used—TIM1 is applied between the silicon die and IHS and TIM2 is used between IHS and thermal solution. TIM materials are usually comprised of a polymer matrix with thermally conductive fillers such as silica, aluminum, alumina, boron nitride, zinc oxide, etc. The polymer matrix wets the contact surface to lower the contact resistance, while the fillers help reduce the bulk resistance by increasing the bulk thermal conductivity. TIM thickness varies by application but is typically between 25 μm and around 250 μm. Selection of appropriate TIM1 and TIM2 materials is necessary for the reliable thermal performance of a product over its life and end-use conditions. It has been observed that during reliability testing, TIM materials are prone to degradation which in turn leads to a reduction in the thermal performance of the product. Typical material degradation is in the form of hardening, compression set, interfacial delamination, voiding, or excessive bleed-out. Therefore, in order to identify viable TIM materials, characterization of the thermomechanical behavior of these materials becomes important. However, developing effective metrologies for TIM characterization is difficult for two reasons: TIM materials are very soft, and the sample thickness is very small. Therefore, a well-designed test setup and a repeatable sample preparation and test procedure are needed to overcome these challenges and to obtain reliable data. In this paper, we will share some of the TIM characterization techniques developed for TIM material down-selection. The focus will be on mechanical characterization of TIM materials—including modulus, compression set, coefficient of thermal expansion (CTE), adhesion strength, and pump-out/bleed-out measurement techniques. Also, results from several TIM formulations, such as polymer TIMs and thermal gap pads, will be shared.

Factors Influencing the Temperature Distribution of 200 W Light Emitting Diode Module Used in the Spotlight

ABSTRACTThe junction temperature of LED (light emitting diode) has a significant impact on its performance and lifetime. In this paper, a simplified model based on the finite element analysis is developed to simulate the temperature distribution of the 200 W LED module using software ANSYS. The model contains LED package, the heat pipe radiator, as well as TIM (thermal interface material) between the LED package and radiator. The temperature distribution of the simulation agrees with that of the experimental measurement. Thickness of TIM affects the heat dissipation significantly, the chips temperature and the maximum temperature difference of chips increases sharply with TIM thickness increasing. Substituting aluminum fins with copper fins cannot improve the heat dissipation performance of heat pipe radiator, and the air velocity of heat pipe radiator plays a key role in the heat dissipation. Thermal conductivity of package submount directly affects the chip temperature and the uniformity of temperature distribution of package submount.

Screen Printed Graphite Nanoplatelet and Nanoparticle Composites for Thermal Interface Materials Application

Screen printed thermal grease of embedded nanoparticles (NPs) on top of graphite nanoplatelets (GNPs) composites are fabricated with pre-defined mesh patterns as a new generation of Thermal interface materials (TIM). In the present study, the NPs thermal grease can be uniformly deposited and reliably controlled thickness in 45 μm in the matrix GNPs. Furthermore, three types of TIM are tested based on the hybridization of GNPs and the nanoparticles (NPs) thermal grease. The hybrid materials are fabricated via screen printing process to ensure the conformal uniformity of NPs thermal grease spreading on the GNPs. The performance of fabricated materials such as temperature, applied pressure, heat flux, and TIM thickness are concurrently tested in the heat flux values in the range of 0---5.3 W cmź2 and the pressure range 0---5.6 kgf/cm2 using a standard TIM tester. The steady-state heat flow technique of ASTM D5470-06 are fully adopted. The measured thermal conductivity of GNPs (3 layers) +NPs (2 layers) composite of a thickness of 195 μm is 0.2 W/m K, compared favorably with the sample of only one layer GNPs (0.11 W/m K). Experimentally, the measured trend in the change of specific thermal conductivity with pressure was in good agreement with the data presented in the literature. In the actual implementation of insulated gate bipolar transistors (IGBT) for 15 kW inverter system used for the renewable energy (solar and wind power), the fabricated composite with GNPs (3 layers) and NPs (2 layers) can effectively reduce the peak temperature of IGBT chip and is very promising in preventing thermally-related failure for the IGBT.

Filler-depletion layer adjacent to interface impacts performance of thermal interface material

When installing thermal interface material (TIM) between heat source and sink to reduce contact thermal resistance, the interfacial thermal resistance (ITR) between the TIM and heat source/sink may become important, especially when the TIM thickness becomes smaller in the next-generation device integration. To this end, we have investigated ITR between TIM and aluminum surface by using the time-domain thermoreflectance method. The measurements reveal large ITR attributed to the depletion of filler particles in TIM adjacent to the aluminum surface. The thickness of the depletion layer is estimated to be about 100 nm. As a consequence, the fraction of ITR to the total contact thermal resistance becomes about 20% when the TIM thickness is about 50 μm (current thickness), and it exceeds 50% when the thickness is smaller than 10 μm (next-generation thickness).

Application of graphite nanoplatelet‐based and nanoparticle composites to thermal interface materials

Thermal interface materials (TIMs) are of crucial importance in improving and enhancing heat transfer in electronic packages, particularly in high-density electronics at regions of exceedingly high temperatures. Commercial TIMs are generally composed of highly conductive particle fillers such as highly thermally conductive graphite and a matrix so that efficient heat transfer and good compliance of the interface material can be achieved during application. Two types of TIMs are tested based on the hybridisation of graphite nanoplatelets (GNPs) and nanoparticles (NPs). The hybrid materials are fabricated via screen printing process to ensure conformal uniformity of NPs spreading on the GNPs. The performance of fabricated materials such as temperature, applied pressure, heat flux and TIM thickness are concurrently tested in the temperature range 40–80°C and the pressure range 0–5.6 kgf/cm2 using a standard TIM tester. The steady-state heat flow technique of American Society for Testing and Materials (ASTM) D5470–06 is fully adopted. For a thickness of 160 μm composite with three-layer GNPs and two-layer NPs, thermal conductivity is measured at ∼0.2 W/m K. In addition, the measured trend in the change of specific thermal conductivity with pressure corresponds well with the data presented in the literature.

Thermal Analysis & Optimization of A 3 Dimensional Heterogeneous Structure

Besides the lot of advantages offered by the 3D stacking of devices in an integrated circuit there is a chance of device damage due to rise in peak temperature value. Hence, in order to make use of all the potential benefits of the vertical stacking a thermal aware design is very essential. The first step for designing a thermal aware architecture is to analyze the hotspot temperature generated by the devices. In this paper we are presenting the results of our thermal analysis experiments of a 3D heterogeneous structure with three layers. The bottom layer had eight identical processors at 2.4 GHz and the top layer was with four memory units. The intermediate layer was a thermal interface material (TIM). The 2D thermal analysis of the top and bottom layers was also done separately. In the next step simulations were carried out by varying TIM thickness and conductivity to study its affect on hotspot temperature so as to optimize the temperature distribution.

Application of Carbon Nanotubes to Thermal Interface Materials

Improvements in thermal interface materials (TIMs) can enhance heat transfer in electronics packages and reduce high temperatures. TIMs are generally composed of highly conductive particle fillers and a matrix that allows for good surface wetting and compliance of the material during application. Two types of TIMs are tested based on the addition of carbon nanotubes (CNTs): one mixed with a commercial TIM product and the other only CNTs and silicone oil. The materials are tested using an in-house apparatus that allows for the simultaneous measurement of temperature, pressure, heat flux, and TIM thickness. Results show that addition of large quantities of CNTs degrades the performance of the commercial TIM, while the CNT-silicone oil mixtures showed improved performance at high pressures. Thickness and pressure measurements indicate that the CNT-thermal grease mixtures are more compliant, with a small increase in bulk thermal conductivity over the range of tested pressures.

Optimization of a Flux-Less Metal Thermal Interface Material by Reflow in a Vacuum Furnace

This paper describes the work performed with a pure metal thermal interface material (TIM) for the sole purpose to improve the transfer of heat from the die to the metal cover case. A flux-less reflow process is employed in order to reflow the indium TIM material. This operation is performed in a vacuum furnace utilizing heat, vacuum, and pressure in a specific sequence in order to wet the metal lid and the backside of the flip chip die. The initial objective was to demonstrate minimal voiding of the TIM and subsequently limited flow out of molten solder from and along the sides of the die. A series of experiments were employed where acceptance criteria is evaluated by a) X-Ray, b) scanning acoustical microscopy (SAM), and c) cross-section. Acceptance criteria consists of 1) indium wetting of both lid to indium interface and indium to silicon interface die, 2) indium bond line (BLT) thickness, 3) lid tilt, and 4) lid shear strength. Acceptance is determined after a subsequent 4X ball grid array (BGA) reflow in a conventional belt reflow furnace with minimal voiding, no popcorn or blistering of the laminate substrate, and TIM thickness and solder flow out at sides of the die within the acceptable limits of the above mentioned criteria.