Search results

Anisotropic conductive film (ACF) offers miniaturization of package size, reduction in interconnection distance and high performance, cost‐competitive packaging and improved environmental impact. However, a major limitation for ACF is the instability caused by thermal warpage. The purpose of this paper is to study the effects of thermal warpage on contact resistance in real time i.e. make online measurements of contact resistance fluctuations while the assembly undergoes thermal shock.

The ACF assemblies are subjected to thermal cycling with different temperature profiles that have peak temperatures either below or above the glass transition temperature (T_g) of the ACF. The flex substrate used was made of polyimide film, with Au/Ni/Cu electrodes and a daisy‐chained circuit matched to the die bump pattern. The ACF used was based on epoxy resin in which nickel and gold‐coated polymer particles are dispersed. A comparative study was carried out on the results obtained.

The results showed that the glass transition temperature (T_g) of the ACF material plays an important role in the high temperature contact resistance. Above T_g, the ACF matrix becomes less viscous, which reduces its adhesive strength and allows the bumps on the chip to slide away from the pads on the substrate. Even though a flex substrate was used in this study, the sliding effect is severe at the corner bumps of the chip, where cumulative forces are generated due to the thermal expansion mismatch. For every thermal cycling profile, there is an incubation period encountered from this work that would have a significant impact in the application of ACF. After the incubation period the contact resistance increased rapidly and the assemblies were therefore no longer reliable.

The work in this paper focuses on contact resistance changes during thermal shock. The paper discusses the reliability issue of ACF during thermal warpage, which is useful to industries using ACF for flip‐chip assemblies.

The purpose of this paper is to present the influence of modifying the fabric surface made from basalt fibers by the magnetron sputtering of chromium and aluminum layers on its resistance to contact heat and comfort properties.

In order to modify the surface of basalt fabric, the process of physical deposition from the gas phase was used. It relies on creating a coating on a selected substrate by applying physical atoms, molecules or ions of specific chemical compounds. The trial of modification was carried out using the magnetron sputtering method due to the material versatility, application flexibility and ability to apply layers on substrates of various sizes and properties.

The findings obtained regarding the heat resistance to contact heat and thermal insulation (comfort) properties show different values depending on the type of metal deposited and the thickness of coating layer. It was found that the modification of basalt fabric surface at the micrometer level changes the tested parameters.

This paper presents the results of resistance to contact heat and thermal insulation properties only for the twill fabric made of basalt fiber. The surface modification of fabric was carried out using the chromium and aluminum of two values of layer thickness (1 and 5 µm).

So far, no tests have been carried out to modify the surface of fabric made from basalt fiber yarns using the magnetron sputtering method. In addition, it has not been studied, how the modification of fabric affects its resistance to contact heat and thermophysiological properties.

The purpose of this paper is to simulate in the time domain three‐dimensional electrical, thermal, mechanical coupled contact problems arising in electric resistance welding (ERW) processes.

A three‐dimensional multiphysical numerical model for analyzing contact problems is proposed. Electrical and thermal field equations in bulk domains are discretized with the cell method (CM). Welding resistance at contact interfaces is described locally by synthetic statistic parameters and contacting domains are matched together by a non‐overlapping domain decomposition method. Contact pressure distribution is resolved by a finite‐element procedure. The model is validated with 3D FEM software package.

The semi‐analytical model describing the electric and thermal resistances at contact interfaces can be easily embedded in CM formulations, where problem variables are expressed directly in integral form. Compatibility conditions between contact members are enforced by a domain decomposition approach. System conditioning and computing time are improved by a solution strategy based on the Schur complement method.

The electrical‐thermal analysis is not coupled strongly with the mechanical analysis and contact pressure distribution is assumed to be not depending on thermal stresses, which can be considerable near the contact area where localized joule heating occurs.

Resistance welding processes involve mechanical, electrical, and thermal non‐linear coupled effects that cannot be simulated by standard commercial software packages. The proposed numerical model can be used instead for designing and optimizing ERW processes.

The paper shows that numerical modeling of ERW processes requires a careful prediction of the localized joule heating occurring at the electrode‐material interface. This effect is reconstructed by the proposed approach simulating coupled electrical, thermal, and mechanical effects on different spatial scales.

The purpose of this research is to study the effect of thickness and surface properties of ZnO solid thin film for heat dissipation application in LED. Heat dissipation in electronic packaging can be improved by applying a thermally conductive interface material (TIM) and hence the junction temperature will be maintained. ZnO is one of the oxide materials and used as a filler to increase the thermal conductivity of thermal paste. The thickness of these paste-type material cannot be controlled which restricts the heat flow from the LED junction to ambient. The controlled thickness is only possible by using a solid thin-film interface material.

Radio Frequency (RF)-sputtered ZnO thin film on Cu substrates were used as a heat sink for high-power LED and the thermal performance of various ZnO thin film thickness on changing total thermal resistance (R _th-tot) and rise in junction temperature were tested. Thermal transient analysis was used to study the performance of the given LED. The influence of surface roughness profile was also tested on the LED performance.

The junction temperature was high (6.35°C) for 200 nm thickness of ZnO thin film boundary condition when compared with bare Cu substrates. Consecutively, low R _th-tot values were noticed with the same boundary condition. The 600 nm thickness of ZnO thin film exhibited high R _th-tot and interface resistance than the other thicknesses. Bond Line Thickness of the interface material was influenced on the interface thermal resistance which was decreased with increased BLT. Surface roughness parameter showed an immense effect on thermal transport, and hence, low R _th (47.6 K/W) value was noticed with low film roughness (7 nm) as compared with bare Cu substrate (50.8 K/W) where the surface roughness was 20.5 nm.

Instead of using thermal paste, solid thin film ZnO is used as TIM and coated Cu substrates were used as a heat sink. The thickness can be controlled, and it is a new approach for reducing the BLT between the metal core printed circuit board and heat sink.

This work aims at constructing a continuous mathematical, linear elastic, model for the thermal contact conductance (TCC) of two rough surfaces in contact.

The rough surfaces, known to be physical fractal, are modelled using a deterministic Cantor structure. Such structure shows several levels of imperfections and including, therefore, several scales in the constriction of the flux lines. The proposed model will study the effect of the deformation (approach) of the two rough surfaces on the TCC as a function of the remotely applied load.

An asymptotic power law, derived using approximate iterative relations, is used to express the area of contact and, consequently, the thermal conductance as a function of the applied load. The model is valid only when the approach of the two surface in contact is of the order of the surface roughness. The results obtained using this model, which admits closed form solution, are displayed graphically for selected values of the system parameters; the fractal surface roughness and various material properties. The obtained results showed good agreement with published experimental results both in trend and the numerical values.

The model obtained provides further insight into the effect that surface texture has on the heat conductance process. The proposed model could be used to conduct an analytical investigation of the thermal conductance of rough surfaces in contact. This model, although simple (composed of springs), nevertheless works well.

The purpose of this paper is to supply an analytical steady-state solution to the heat transfer equation permitting to fast design investigation. The capability to efficiently transfer the heat away from high-powered electronic devices is a ceaseless challenge. More than ever, the aluminium or copper heat spreaders seem less suitable for maintaining the component sensitive temperature below manufacturer operating limits. Emerging materials, such as annealed pyrolytic graphite (APG), have proposed a new alternative to conventional solid conduction without the gravity dependence of a heat-pipe solution.

An APG material is typically sandwiched between a pair of aluminium sheets to compose a robust graphite-based structure. The thermal behaviour of that stacked structure and the effect of the sensitivity of the design parameters on the effective thermal performances is not well known. The ultrahigh thermal conductivity of the APG core is restricted to in-plane conduction and can be 200 times higher than its through-the-thickness conductivity. So, a lower-than-anticipated cross-plane thermal conductivity or a higher-than-anticipated interlayer thermal resistance will compromise the component heat transfer to a cold structure. To analyse the sensitivity of these parameters, an analytical model for a multi-layered structure based on the Fourier series and the superposition principle was developed, which allows predicting the temperature distribution over an APG flat-plate depending on two interlayer thermal resistances.

The current work confirms that the in-plane thermal conductivity of APG is among the highest of any conduction material commonly used in electronic cooling. The analysed case reveals that an effective thermal conductivity twice as higher than copper can be expected for a thick APG sheet. The relevance of the developed analytical approach was compared to numerical simulations and experiments for a set of boundary conditions. The comparison shows a high agreement between both calculations to predict the centroid and average temperatures of the heating sources. Further, a method dedicated to the practical characterization of the effective thermal conductivity of an APG heat-spreader is promoted.

The interlayer thermal resistances act as dissipation bottlenecks which magnify the performance discrepancy. The quantification of a realistic value is more than ever mandatory to assess the APG heat-spreader technology.

Conventional heat spreaders seem less suitable for maintaining the component-sensitive temperature below the manufacturer operating limits. Having an in-plane thermal conductivity of 1,600 W.m⁻¹.K⁻¹, the APG material seems to be the next paradigm for solving endless needs of a thermal designer.

This approach is a practical tool to tailor sensitive parameters early to select the right design concept by taking into account potential thermal issues, such as the critical interlayer thermal resistance.

Thermal performances are key factors impacting the operation of angular contact ball bearings. Heat generation and transfer about angular contact ball bearings, however, have not been addressed thoroughly. So far, most researchers only considered the convection effect between bearing housings and air, whereas the cooling/lubrication operation parameters and configuration effect were not taken into account when analyzing the thermal behaviors of bearings. This paper aims to analyze the structural constraints of high-speed spindle, structural features of bearing, heat conduction and convection to study the heat generation and transfer of high-speed angular contact ball bearings.

Based on the generalized Ohm’s law, the thermal grid model of angular contact ball bearing of high-speed spindle was first established. Next Gauss–Seidel method was used to solve the equations group by Matlab, and the nodes temperature was calculated. Finally, the bearing temperature rise was tested, and the comparative analysis was made with the simulation results.

The results indicate that the simulation results of bearing temperature rise for the proposed model are in better agreement with the test values. So, the thermal grid model established is verified.

This paper shows an improved model on forecasting temperature rise of high-speed angular contact ball bearings. In modeling, the cooling/lubrication operation parameters and structural constraints are integrated. As a result, the bearing temperature variation can be forecasted more accurately, which may be beneficial to improve bearing operating accuracy and bearing service life.

A theory for the thermal resistance in adhesive joints between semiconductor dice and substrates has been developed. The theory takes into account the thermomechanical shear stress in the bond layer caused by differences in thermal expansion. The theoretical result indicates that only small reductions in thermal resistance can be obtained by increasing the bulk thermal conductivity of the adhesive by filling it with silver particles. Experiments were carried out in order to verify this effect. An epoxy resin was loaded with various amounts of silver particles and used to bond thermal test chips to copper substrates. There was a surprisingly small difference in thermal resistance between the various adhesives. The difference was considerably less than the difference in bulk thermal conductivity indicated, thus confirming the basic result of the theory.

This paper aims to perform thermal and mechanical characterization for silver-based sintered thermal joints. Layer quality affects thermal and mechanical performance, and it is important to achieve information about how materials and process parameters influence them.

Thermal investigation of the thermal joints analysis method was focused on determination of thermal resistance, where temperature measurements were performed using infrared camera. They were performed in two modes: steady-state analysis and dynamic analysis. Mechanical analysis based on measurements of mechanical shear force. Additional characterizations based on X-ray image analysis (image thresholding), optical microscope of polished cross-section and scanning electron microscope image analysis were proposed.

Sample surface modification affects thermal resistance. Silver metallization exhibits the lowest thermal resistance and the highest mechanical strength compared to the pure Si surface. The type of dynamic analysis affects the results of the thermal resistance.

Investigation of the layer quality influence on mechanical and thermal performance provided information about different joint types.

Increasing power densities within electronic equipment have led to a rise in the number of heat related problems being experienced. This paper describes the use of computerised thermal analysis techniques to optimise the design of passive thermal management systems for electronic equipment.