Heat Sink Attachment Research Articles

Thermal Interface Materials in the HPC Era

The high performance computing (HPC) module market is seeing some enormous simultaneous changes. The compute needs of XPU and tensor processors are causing die area to grow, with higher areal power density, and HBM DRAM stacks are now located immediately adjacent to the processor. The paper will discuss how metallic thermal interface materials are providing the low thermal resistance, high reliability and flexibility for advanced compute modules and systems, in both TIM1 (die-lid), TIM 2 (lid-heatsink) and TIM 0 (1.5) (die to heatsink) applications. Reflowed indium as a TIM1 has a nearly two decade performance record in high volume production, where a combination of CTE matching and very high relative bulk thermal conductivity is highly advantageous. This presentation will discuss the latest developments on indium and other metal alloys as known good solderable solutions that have demonstrated very high bulk thermal conductivity, relative to more common polymer TIMs for TIM1 applications, as well illustrating engineered variations of indium alloys that do not require a solder reflow process, eliminating manufacturing process steps. Discussion also includes metallic TIMs designed for use in TIM0 (TIM1.5) applications with the compression inherent in heat sink attachment with mechanical retention. Novel liquid-metal-based solutions are also under development, and the paper will describe some ways in which gallium alloys are providing ways to resolve some of the conflicting requirements (such as pressure and thinned die and reliability) of emerging applications.

Effectiveness of heat sink fin position on photovoltaic thermal collector cooling supported by paraffin and steel foam: An experimental study

Forced convective cooling effectiveness on photovoltaic thermal collector electrical and thermal performance was experimentally studied with phase change material (paraffin) + steel foam mixture and two different angular positioned finned heat sink attachments. Fins are positioned flat and inclined, and air was forced with fan to flow between them. Solar radiation, temperature, electrical and thermal power, energy, and exergy efficiencies were determined and compared with reference photovoltaic module data. The first photovoltaic thermal collector was constructed with phase change material (paraffin) + steel foam mixture application to the back surface and covering with an incline finned heat sink. The second one was assembled with phase change material (paraffin) + steel foam filling to back surface and covering with a flat finned heat sink. Incline and flat finned heat sink attached collectors were cooled 12.23% and 21.67% relatively more than photovoltaic module. Electrical efficiency improvement with incline finned and flat finned heat sink application acquired approximately 5.09% and 6.18% relative to the photovoltaic module, which has 4.38% electrical efficiency, thanks to the cooling provided. The overall efficiencies were 41.4% and 59.53%. Photovoltaic module exergy efficiency is 4.67%, it is increased to 5.59% and 6.87% by cooling with incline finned heat sink and flat finned heat sink applications. Utilizable energy enhancement is identified approximately 140.32 kWh/year and 207.42 kWh/year by assuming 2738 h annual sunshine time in Turkey. These potentials rely on increase in electrical efficiency and heat recovery during cooling of PV/T collectors with incline and flat finned heat sinks. The predicted energy profit can be estimated at $7.01/year and $10.37/year, and its equivalent in emission reduction can be 115.76 kg·CO2/year and 171.12 kg·CO2/year.

Optimal design and placement of heat sink elements attached on a cylindrical heat-generating body for maximum cooling performance

With the increasing usage of miniature electronic pieces, utilizing new cooling techniques and dissipating heat from these components are essential. In this regard, heat sinks are efficient tools for removing heat from hot mediums and improving their thermal performance. The purpose of this study is to reduce the highest temperature of a cylindrical heat-generating body by geometric design of heat sink attachments on the device’s top surface. Six configurations are proposed for the shape of the heat sinks. For a fixed total area of the heat sink attachments, it is proven that there exist optimal configurations, locations and geometric parameters of the heat sink attachments that thermally perform the best among the others. Found to yield the best cooling performance, the ‘semi-triangular-shaped’ heat sinks reduce the highest temperature of the hot medium around 60 % more than the circular-shaped heat sinks.

Optimal placement and sizing of heat sink attachments on a heat-generating piece for minimization of peak temperature

The lifespan of many components depends on their operating temperature. Heat sinks are used to extract heat from heat dissipating devices to avoid overheating and mechanical-electrical loss. Therefore, it is critical to optimally distribute the heat sink attachments to reach the minimum excess (peak) temperature. This paper documents the optimal location of heat sinks mounted on a heat-generating (electronic) piece. The optimization objective is to minimize the peak temperature when the total surface area of the attachments is fixed. Heat sink attachments are distributed on the top surface of the hot piece in several uniform and non-uniform arrangements. For each number of heat sources, the results show that there exists an optimal arrangement which thermally performs the best. In the case of two and three heat sinks, the optimal distributions are columnar and the triangular arrangements, respectively. The increase in the number of the heat sinks results in thermal performance improvement. The highest temperature of double heat sinks configuration is about 28% lower in comparison with the single heat sink. It is also indicated the thermal performance of the elongated shape is higher compared to the circular shape.

Comparisons of Soldering Alloys in Large Ceramic Substrate to Metal Heatsink Attachment Application

Abstract Tin-lead alloys have historically been popular in the electronics industry for use in solder-attach applications. Despite recent restrictions related to lead content, some industries continue to use lead based alloys in solder applications. Tin-lead based alloys, in particular, have proven to have excellent solderability to tin, nickel, copper, gold, and silver metallization surfaces. They have also performed better in reliability than most of the lead free solders. As a result of this, they are still widely used in the aerospace and military electronics industry. Hybrid microelectronics built for space applications use both Tin-Lead-Silver Alloy Sn62 and Lead Free Soldering Alloy Sn96; these solders are used both for wire and component attach as well as substrate to header attach. This article discusses the differences of these two solders, using both literature and experimental study. Experimental testing involving pull tests further supports this conclusion.

Enhancing PV modules efficiency and power output using multi-concept cooling technique

The efficiency and power output of a PV module decrease at the peak of sunlight due to energy loss as heat energyand this reduces the module power output. Multi-concept cooling technique, a concept that involves three types of passive cooling, namely conductive cooling, air passive cooling and water passive cooling has the potential to tackle this challenge. The experiment was set up using two solar panels of 250 watts each with both modules mounted at a height of 37 cm to create room for air-cooling, with the application of water-cooling at the surface of one of the PV modules to reduce the surface temperature to 20 ∘C. The rear of the same module attached to an aluminium, Al heat sink. The other module also mounted was without water-cooling and Al heat sink attachment. The Al heat sink comprises aluminium plate attached with aluminium fins to aid cooling, and water at a reduced temperature achieved with the introduction blocks of ice facilitated the module surface cooling. Analysis of the power output achieved, carried out with the help of the equation for PV array power output with a derating factor of 80%. The experiment recorded an increase in output power of 20.96 watts, and an increase in efficiency of not less than 3% achieved thus making the module more efficient and productive.

A HIGH THROUGHPUT, LOW COST ASSEMBLY APPROACH FOR LED IMS PACKAGES TO HEAT SINK USING ADVANCED THERMAL INTERFACE MATERIALS

The objective of this study is to design and fabricate a high reliability LED Insulated Metal Substrate (IMS) package to complex heat sink attachment using an advanced thermal interface material (TIM). The assembly consists of LED IMS parts bonded to a heat spreader/sink using an advanced TIM and a corner bond material to quickly and accurately secure the LEDs in position. The corner bond adhesive is snap cured for fast machine cycle times while the high performance, high adhesion TIM materials cure throughout the rest of the assembly operation. This approach allows high accuracy LED bonding without the need for alignment pins or fasteners to anchor to the IMS. The IMS attached to the heat sink is then electrically interconnected with a thin flex substrate on top of the IMS. This approach is expected to replace the current mechanical fastners and low strength silicone TIM materials and reduce the cycle time and overall placement cost which are key drivers especially for the automotive industry.

Study of Thermally Enhanced 2.5D Packages with Multi-chips Molded on Silicon Interposer

The 2.5D package with distributed vias on silicon interposer has received great attention due to its potential for heterogeneous integration. The overmolded 2.5D package protects the silicon die and interposer from environmental damage, which, on the other hand, induces undesirable thermal resistance due to low thermal conductivity of the molding compound. In this paper, a thermally enhanced 2.5D package with exposed die is proposed, fabricated and examined from the thermal enhancement viewpoint. The high power thermal test die was first assembled on a silicon interposer with through silicon vias and connected to the substrate, which was followed by the overmolding and back-grinding processes to form the partially molded (PM) package with exposed die for direct heat sink attachments. Experiments were conducted to examine the thermal performance under different thermal conditions. Under natural convection without thermal enhancement, there was no performance difference between the PM package and the overmolded package. However, when the package top was mounted with a thermally enhanced structure such as a pin fin heat sink, the thermal resistance of PM package was significantly reduced. The advantage was more prominent with the attachment of a high performance liquid cooling heat sink. Thermal simulation models were also constructed to examine the thermal performances under different test conditions, and the realistic thermal interface resistance of 0.5 Kcm2/W was estimated based on the package warpage. The computed thermal resistances agreed with measurement results.

Liquid Phase Sintered Solders with Indium as Minority Phase for Next Generation Thermal Interface Material Applications

Because of their very high thermal conductivity, low melting point, and high shear compliance, indium-based materials are excellent candidates for thermal interface material (TIM) applications for packaging thermally sensitive next-generation devices. However, currently used indium-based solders suffer from 2 serious shortcomings: (i) high cost due to high indium content, and (ii) very low compressive strength and creep resistance which may lead to structural instability following heat-sink attachment. In order to circumvent these problems, and also introduce a built-in melting point hierarchy following initial reflow, a radically different approach for producing microelectronic solder TIMs based on liquid phase sintering (LPS) is being developed. In this paper, we report on the processing and characterization of LPS Sn-In solders, the microstructure of which consists predominantly of particles of the high melting phase (HMP) Sn and a smaller amount of intergranular low melting phase (LMP) In. By optimizing the In content, highly compliant LPS solders with flow stresses close to that of pure In were obtained. The electrical and thermal conductivity of the LPS solder was found to be about half that of pure In. It is demonstrated that metallurgically good joints can be produced between this new solder and Cu substrates during a single step which combined LPS with joining. The contact thermal resistance of the internal grain boundaries was estimated, and it is inferred that because of the numerous internal boundaries, the solder/substrate interfaces have relatively small effect on the joint resistance. Based on the estimated boundary resistance, a previously developed model was utilized to predict the thermal conductivity of the LPS solder as a function of HMP volume fraction and particle size.

Analysis and Prediction of Vibration-Induced Solder Joint Failure for a Ceramic Column Grid Array Package

Solder joint fatigue failure under vibration loading continues to be a concern in microelectronic industry. Existing literature has not adequately addressed high-cycle fatigue failure of high-lead solder joints, especially under a broad spectrum of vibration frequencies. Also, damage mapping across solder joints in an area-array package has not been effectively studied using numerical models and experimental cross sectioning. This paper aims to develop an experimental and modeling approach that can accurately determine the solder joint behavior of electronic components under vibration conditions. In particular, this paper discusses the out-of-plane sinusoidal vibration experiments at 1G, numerical modeling, and fatigue life prediction for a 42.5×42.5×4mm3 1089 input∕output ceramic column grid array (CCGA) package on a 133×56×2.8mm3 FR4 board. Detailed investigation and characterization involving dye-and-pry analysis, microstructural examination, and numerical modeling enabled the development of a high-cycle stress-based equation for lead-containing CCGA under sinusoidal loading. The developed approach has been applied to a number of cases including a CCGA package with a heat sink as well as a CCGA package subjected to frequency sweeps. It is seen that the predictions from the developed model agree well with experimental data and that the developed model can map the evolution of solder damage across all solder joints and can also provide important design recommendations in terms of solder joint location as well as heat sink attachment.

Reliability of Pressure-Sensitive Adhesive Tapes for Heat Sink Attachment in Air-Cooled Electronic Assemblies

This study investigates the reliability of commercially available pressure-sensitive adhesive (PSA) tapes used for electronic component-to-heat sink attachment. It is found that creep can affect the PSA reliability. Therefore, creep is experimentally characterized using isothermal, constant load, double lap shear measurements in conditions representative of vertically oriented heat sink applications. PSA joint life predictions are derived from the accelerated creep characteristics using a secondary creep model. The creep resistance of a laminated silicone/aluminum/acrylic PSA tape is found to be significantly lower than that of a single-layer acrylic tape. This suggests that the potential impact of tape creep on joint reliability should be carefully evaluated as a function of tape chemistry/construction and application environment. Furthermore, the sensitivity of PSA creep characteristics to both operating temperature and heat sink weight highlights the need for thermally optimized, least-weight heat sink designs.

Thermal and Mechanical Loading Effects on the Reliability of Organic Flip Chip Package

The silicon die of an organic flip chip assembly is exposed to external mechanical loads during component testing and heat sink attachment. These loads can potentially cause package to flexure and may eventually lead to severe damage in the die and package. A comprehensive evaluation has been conducted to determine the maximum loading limit of organic flip chip package through design of experiment (DOE) approach. A material testing system has been utilized to simulate various loading conditions (ranging from 15 lb to 200 lb) on organic flip-chip test vehicles (FTV) during heat sink attachment. The effects of permanent mechanical loading and thermal cyclic loading on the reliability of FTV structures are also investigated in this study. Three-dimensional finite element models (FEM) of FTV have been employed to aid in understanding the mechanical behavior of silicon die and organic substrate under both loading conditions. Shadow Moire´ technique has been used to measure the out-of-plane residual deformation of the FTV that underwent simulated loading conditions. These components were then visually inspected and tested functionally. Results were summarized and used as indicator of package reliability.

Thermal performance of a low‐cost thermal enhanced plastic ball grid array package ‐ NuBGA

NuBGA is a low‐cost, single‐core, two‐metal layer, cavity‐down plastic ball grid array package. With special design concepts, NuBGA provides electrical and thermal enhancements for electronic packaging applications. The concepts of these innovative designs are briefly described. Thermal resistance of junction to air is investigated first by finite element simulations, and the results are then compared to experimental measurements. Also, thermal measurements are carried out for both with, and without, heat sink attachment. Geometric dependence of thermal resistance on structural parameters such as thickness of the copper heat spreader and organic substrate, power and ground planes in printed circuit board (PCB), and the size of PCB are also discussed.

Metallization for diode lasers

This paper reviews some of the problems associated with injection laser heat-sink attachment and ohmic contact metallurgy. The effects these have on initial laser characteristics as well as on laser reliability are discussed for both (AlGa)As (0.8 μm) lasers and the newer InGaAsP (1.3 μm) lasers.

The path of a projectile

The efficiency and power output of a PV module decrease at the peak of sunlight due to energy loss as heat energyand this reduces the module power output. Multi-concept cooling technique, a concept that involves three types of passive cooling, namely conductive cooling, air passive cooling and water passive cooling has the potential to tackle this challenge. The experiment was set up using two solar panels of 250 watts each with both modules mounted at a height of 37 cm to create room for air-cooling, with the application of water-cooling at the surface of one of the PV modules to reduce the surface temperature to 20 ∘C. The rear of the same module attached to an aluminium, Al heat sink. The other module also mounted was without water-cooling and Al heat sink attachment. The Al heat sink comprises aluminium plate attached with aluminium fins to aid cooling, and water at a reduced temperature achieved with the introduction blocks of ice facilitated the module surface cooling. Analysis of the power output achieved, carried out with the help of the equation for PV array power output with a derating factor of 80%. The experiment recorded an increase in output power of 20.96 watts, and an increase in efficiency of not less than 3% achieved thus making the module more efficient and productive.