Hybrid power modules using a metal matrix composite baseplate: An evaluation

The cubic silicon carbide (3C-SiC) has been considered as a candidate structural material for several types of advanced nuclear reactors. The effects of cascade collision on thermal conductivity in symmetrical tilt grain boundary (GB) were studied by Molecular dynamics (MD) simulations. The thermal conductivity of 3C-SiC at Σ5(210)[001] GB was calculated using non-equilibrium molecular dynamics (NEMD) methods. A relatively small simulation unit was used to analyze the effect of different energies of incident PKA (primary knock-on atoms) on the thermal conductivity of 3C-SiC and to compare the results with perfect structure GB system. Finally, the vibrational density of states (VDOS) of atoms in the GB region was calculated to analyze the phonon mismatch at the interface. Calculations show that cascade collisions generated by energetic atoms will result in a decrease in thermal conductivity of the Σ5(210) GB system, but the effect varies in different regions, with a sharp decrease in thermal conductivity and an increase in thermal resistance for the intracrystalline region, while the magnitude of change in either thermal resistance or thermal conductivity is not significant in the GB region. Irradiated model shows a higher GB energy compared to the unirradiated model. For all irradiated models, lattice defects have a significant effect on the thermal conductivity of the GB system, depending on the spatial structure of the GBs. the results of the VDOS analysis suggest that an increase in the degree of atomic lattice mismatch near the interface is responsible for a further increase in the thermal resistance of the irradiated GB system.

A study of thermal cycling endurance of three different die attach adhesives by measuring the increase in thermal resistance during a thermal cycling test is discussed. Test chips were bonded to three substrates with different coefficients of thermal expansion. The thermal resistance increased with increased number of temperature cycles. A large mismatch in thermal expansion gave the fastest increase in thermal resistance. The study also revealed a significant difference in behavior between the different adhesives. >

Despite the availability of various materials for chimney applications, ongoing research seeks alternatives with improved thermal and chemical resistance. Geopolymers are a promising solution, exhibiting exceptional resistance to high temperatures, fire, and aggressive chemicals. This study investigates fly ash-based lightweight geopolymer concretes that incorporate expanded clay aggregate (E.C.A.), perlite (P), and foamed geopolymer aggregate (F.G.A.). The composites were designed to ensure a density below 1200 kg/m3, reducing overall weight while maintaining necessary performance. Aggregate content ranged from 60 to 75 wt.%. Physical (density, thickness, water absorption), mechanical (flexural and compressive strength), and thermal (conductivity, resistance) properties were evaluated. F.G.A. 60 achieved a 76.8% reduction in thermal conductivity (0.1708 vs. 0.7366 W/(m·K)) and a 140.4% increase in thermal resistance (0.1642 vs. 0.0683). The F.G.A./E.C.A./P 60 mixture showed the highest compressive strength (18.069 MPa), reaching 52.7% of the reference concrete's strength, with a 32.3% lower density (1173.3 vs. 1735.0 kg/m3). Water absorption ranged from 4.9% (REF.) to 7.3% (F.G.A. 60). All samples, except F.G.A. 70 and F.G.A. 75, endured heating up to 800 °C. The F.G.A./E.C.A./P 60 composite demonstrated well-balanced performance: low thermal conductivity (0.2052 W/(m·K)), thermal resistance up to 1000 °C, flexural strength of 4.386 MPa, and compressive strength of 18.069 MPa. The results confirm that well-designed geopolymer lightweight concretes are suitable for chimney and flue pipe linings operating between 500 and 1000 °C and exposed to acidic condensates and aggressive chemicals. This study marks the initial phase of a broader project on geopolymer-based prefabricated chimney systems.

The high efficiency of the method of grafting functionally active polymer to fibres from aliphatic polyamides to increase their thermal and chemical resistance has been demonstrated. When the easily oxidized PDMAEM, quaternary ammonium or pyridinium bases, especially in the presence of an epoxy group in the N-alkyl radical, is contained in the grafted chains, the increase in thermal resistance and chemical stability is caused by an effect of thermooxidative cross-linking of the polymer, accompanied by a loss in its thermal plasticity.

Numerical simulation of the temperature distortions in InGaP/GaAs/Ge solar cells working under high concentrating conditions due to voids presence in the solder joint

The effects of ceria on the mechanical properties and thermal shock resistance of thermal sprayed NiAl intermetallic coatings

Analysis of solder joint reliability of high power LEDs by transient thermal testing and transient finite element simulations

Thermal simulation of joints with high thermal conductivities for power electronic devices

The primary objective of the research presented in this paper is to qualify the reliability of mixed assemblies by comparing them to the conventional Sn-Pb assembly and completely Pb-free assembly. The research investigates both forward and backward compatibility in electronic assemblies using a design of experiments (DOE) approach. The investigation utilized a test vehicle containing an area array component (BGA169) and chip components (0603 resistors). Hot air solder leveling (HASL) and organic solderability preservative (OSP) surface finishes were used on the test vehicles to represent Sn-Pb and Pb-free alternatives, respectively. The assembled test vehicles were cut into two panels - one containing a resistor section for isothermal aging and the other containing a BGA and another resistor section for thermal shock. The assemblies were subjected to isothermal aging and thermal shock tests as per Interconnecting and Packaging Electronic Circuits/Joint Electronic Device Engineering Council (IPC/JEDEC) standards. The resistors were sheared in the as-soldered condition, and at various isothermal aging intervals and thermal shock cycles. In order to simulate an intermetallic failure in isothermal aging, a reduced shear height (20 mum) was used for the shear test. The performance of the resistor solder joints were quantified in terms of the shear force. The performance of the ball grid array (BGA) solder joint during thermal shock testing was quantified in terms of the number of cycles to failure. Experimental results from shear analysis of resistor solder joints show that Pb-free alloy assemblies' performance is superior to those assembled using Sn-Pb alloy. Also, the ductile nature of the Sn-Ag-Cu (SAC) alloy provides the joints a better fatigue life. With the area array components, Pb-free assembly joints outlived the traditional Sn-Pb joints when subjected to thermal shock loading. Among the mixed assemblies, backward-compatible assemblies (Pb-free bumps and Sn-Pb solder alloy) showed superior performance. The microstructural analysis of the solder joints indicate a uniform distribution of lead in the solder joint matrix.

A series of experiments on one commonly available loose-fill fiberglass attic insulation has been performed using the guarded hot box capability of the Large Scale Climate Simulator at the Oak Ridge National Laboratory. These experiments were conducted using an attic test module that was built to simulate typical residential construction. Under simulated winter conditions, the surface-to-surface thermal resistance between the bottom of the gypsum board and the top of the insulation was found to decrease substantially as the surface-to-surface temperature difference increased from 10 to 40 K. At the largest temperature differences, the resistances were as much as a factor of two lower than the estimated nominal thermal resistance of the insulation. This change in thermal resistance has been attributed to natural convection within the insulation. It should be noted that the present experiments were performed with one type of loose-fill fiberglass insulation, and the results may not be applicable to other loose-fill insulations with different air flow and thermal properties. A series of experiments was also performed with various materials laid on top of the insulation. The most effective of these covering systems produced increases in thermal resistance of more than 100 percent at the largest temperature differences, and appeared to nearly eliminate heat transfer by natural convection in the temperature range investigated.

In pursuit of sustainable energy solutions and to combat the environmental challenges posed by fouling in thermal devices, this study developed Ni-P-TiO2 and Ni-P-Polytetrafluoroethylene (Ni-P-PTFE) surfaces and explored the effectiveness of coatings in minimizing fouling on heat exchange surfaces. We conducted heat exchange experiments to compare the both coating surfaces with copper surface under identical clean conditions in microchannels. Further analyses explored fouling resistance across surfaces at various flow rates and solution hardness, complemented by Scanning Electron Microscope (SEM) images of fouling morphology. The findings revealed that decreasing surface energy and enhancing hydrophobic properties can reduce crystal fouling. Notably, both Ni-P-TiO2 and Ni-P-PTFE surfaces demonstrated superior performance, showing significantly lower thermal resistance compared to copper surface. Despite the increase in thermal resistance with solution concentration, the growth rate of fouling resistance declined gradually. The Ni-P-PTFE coating, benefiting from its lower surface energy and greater hydrophobicity, showed superior looseness and porosity. This study demonstrates the effectiveness of Ni-P-TiO2 and Ni-P-PTFE coatings in reducing fouling thermal resistance, offering a promising approach for improving microchannel device performance.

The use of local biomaterials in construction is becoming an imperative to save the planet and to reduce the cost of construction in sub-Saharan region. The aim of this research work is to study the effect of the mucilage of Grewia bicolor fiber on the properties of mud bricks. the mucilage from Grewia bicolor bark was used to stabilize raw earth bricks. Two formulations of samples are obtained. The first one is with 100% of soil and without mucilage. The second one the soil stabilized with mucilage at three different viscosities (25.30s, 20s and 10s). The output measurement are compressive and flexural strengths, as well as the thermal conductivity, thermal resistance and thermal effusivity of the composite material formulated. The results show an increase in compressive strength with the increase in viscosity of the mucilage. An increase in flexural strength when the viscosity of the mucilage is increased. A decrease in thermal conductivity when the viscosity of the mucilage is increased. An increase in thermal resistance when the viscosity of the mucilage is increased. Effusivity decreased with increasing of mucilage viscosity. These results show that the mucilage of Grewia bicolor can significantly improve the characteristics of mud bricks and this may have potential use in eco-construction for habitat.

Research was carried out on the influence of various silicone compounds on the properties of pressure-sensitive adhesives. Silicone-based pressure-sensitive adhesives have good self-adhesive properties and are used in many different industries. However, their thermal resistance is relatively low. In order to improve this property, modifications were made to these adhesives. Compositions were tested, such as viscosity or thermogravimetric analysis, as well as tests of finished products in the form of self-adhesive tapes, i.e., peel adhesion, tack, cohesion at room and elevated temperature, SAFT test (Shear Adhesive Failure Temperature), pot-live (viscosity) and shrinkage. During the tests, an increase in thermal resistance (225 °C), lower shrinkage (0.08%), and lower viscosity was achieved (16.5 Pas), which is a positive phenomenon in the technology of pressure-sensitive adhesives. Thanks to this research, the properties of silicone self-adhesive adhesives have been significantly improved.

The crack propagation in solder joints is detected by measuring the relative thermal resistance using transient thermal analysis. The method can be applied on high power devices which have to dissipate a significant amount of thermal load through the solder joint. The thermal load in the device is switched and the forward voltage of the junction is measured in time resolved modality. As published earlier, to obtain the relative thermal resistance the dissipated power of the device and the proportional factor (k-factor) between temperature and forward voltage are not required when the time resolved forward voltage curves are normalized [1]. Aim of the research was to investigate the concept and the sensitivity of the measuring method using high power ceramic LED packages. For prove of sensitivity, two batches of high power LEDs were soldered on PCBs, i.e. aluminum insulated metal boards (Al-IMS): one batch with SAC305 and the other one with a SAC+ (Innolot) solder. The test modules were exposed to typical temperature cycles of -40°C / +125°C as required for automotive applications. With standard test methods differences in reliability, i.e. thermo mechanical fatigue, of the two solders were very difficult to detect for the module design under these test conditions [2]. First, we investigated the relative thermal resistance after defined number of cycles at room temperature. To define a realistic failure criterion for calculation of the cumulative failure probability, we have set-up a finite element model and simulated the transient temperature curves. The increase of measured relative thermal resistance is critically compared and calibrated with transient finite element simulations. The Weibull curves were determined based on the failure criteria describing a 70% cracked solder area. Then, after resolving a significant difference in the increase of thermal resistance of the two solders, an In-Situ test system was set up and measurements were performed, i.e. a set of samples was measured in the temperature chamber under hot and cold condition.

An investigation on the deterioration of physical and mechanical properties of granite after cyclic thermal shock