Sintering silver paste has attracted ever-increasing attention in the electronic packaging field due to high melting point, excellent thermal conductivity and ease of process, which is even considered as the most promising mainstream bonding material for WBG power devices. However, the high current density and high-power density of WBG power devices lead to the generation of large amounts of heat, which brings about thermal stress between sintered silver layer and die/substrate, and sintered silver joints easily suffer reliability problem. In this paper, the effect of Young's modulus on the reliability of sintered silver will be systematically investigated from two aspects: simulation and experiment. In terms of simulation, a sequential thermodynamic coupling method based on finite element analysis (FEA) is used to investigate the reliability of sintered silver. We obtained data on the evolution of Mises stress and plastic strain for sintered silver with different Young's modulus under power cycles (PC), and firstly found three plastic strain cumulative trends corresponding to the three Young's modulus ranges for sintered silver and analyzed the effect of Young's modulus on reliability based on them. Experimentally, we can obtain various microporous sintered silver with different Young's modulus and different shear strengths by changing the sintering parameters, and their porosity and pore size distribution are counted in detail. We systematically and orderly analyze the correlation between sintering parameters, microstructure, Young's modulus and reliability of sintered silver.
Two experiments were conducted to investigate the effect of RH (35, 60, and 85%) on thermoregulation of broiler chickens at high (35 ° C) and mild (30 ° C) temperatures at the age of 4 wk. The effects of humidity on rectal temperature (RT) and plumage temperature at back (PBAT) and skin temperature at breast (SBRT) were determined at 1, 4, 8, 16, and 24 h after exposure. The RT, PBAT, and SBRT were all significantly increased by high temperature (35 ° C). Humidity had a significant influence on RT at 35 ° C but not at 30 ° C. The peripheral temperatures (PBAT and SBRT) were significantly affected by humidity but responded differently at high (35 ° C) compared with mild temperature (30 ° C). In conclusion, high humidity above 60% impaired the heat transmission from body core to the periphery at 35 ° C but facilitated it at 30 ° C in 4-wk-old broiler chickens. The effect of humidity on nonevaporative heat loss was depended on air temperature, as nonevaporative heat loss was suppressed by high humidity (>60% RH) at high temperature but enhanced at the mild temperature. The effect of humidity on the relationship between peripheral and core temperature depends on ambient temperature as well as on the age of the broiler chicken. The disturbance of thermal balance could not be determined only by changes in RT or peripheral temperature at a single time point but could be determined by mean body temperature within a certain time frame.
The morphology of filler has an important effect on the electrical conductivity and electromagnetic shielding properties of conductive polymer composites (CPCs). In this work, three different nickel powders include spherical nickel (S-Nickel) powder, flaky nickel (F-Nickel) powder, and chain spherical nickel (CS-Nickel) powder were mixed into two-component silica gel and epoxy resin to obtain CPCs, respectively. The electrical conductivity, electromagnetic interference shielding effectiveness (EMI SE), compressibility, and tensile strength of CPCs were investigated. The results show that CPCs with CS-Nickel have the best electrical conductivity and EMI SE, due to the excellent dimensional structure of CS-Nickel result in the denser conductive network. At the same time, compared with silica gel, epoxy resin has a higher cohesion force to fillers, and epoxy resin CPCs show better electromagnetic shielding performance with lower filler content. We believe that our work can provide some experimental support for the selection of filler and matrix for high performance electromagnetic shielding materials.
High-purity silver nanowires (AgNWs) with an average width of 60 ± 5 nm and a typical length of 10–20 μm were synthesized conveniently at a relatively high AgNO3 concentration of 0.3 M through a CuCl2 and stainless steel co-mediated polyol reduction method.
Anhydride and amine epoxy systems are widely used as hardeners in underfill materials for flip chip packaging. A comparison was made between these two systems in order to evaluate the comprehensive performance of the resulting underfill. It was found that the addition of multi-size silica particles has little effect on the curing reaction of the epoxy mixture while a significant effect on increasing the viscosity, storage modulus, Tg and lowering the CTE and the magnitude of the tanS peak with the increase of SiO 2 loading for both anhydride and amine curing system. Moreover, with the same filler loading, compared with the amine based underfill, the anhydride system exhibited much lower viscosity, glassy modulus, and CTE in the glassy region and lower Tg thus showing a potential for flip chip underfilling applications.
Detection of neurotransmitters at the single-cell level is essential for understanding the related biological processes and neurodegenerative diseases. We report a dual-nanopore biosensor utilizing a DNA aptamer probe to specifically interact with dopamine, enabling detection of intracellular dopamine and dopamine efflux (extracellular dopamine) in a single pheochromocytoma (PC12) cell. We demonstrate the ability to form an intrapipette electric circuit with the dual-nanopore configuration, which is crucial to achieving both intracellular and extracellular dopamine detection. The sensor allowed rapid detection of dopamine in 10 min with a limit of detection of 0.4 nM. We show the dual-nanopore biosensor was able to monitor single-cell dopamine concentration change under different stimulations. The developed dual-nanopore biosensor represents a novel strategy for time-dependent monitoring of neuron behavior at the single-cell level and potentially can be extended to other platforms for single-cell analysis.
Considering the requirements of Microsystems miniaturization integration for high-performance film-forming substrates, the key technologies of multilayer BCB/Cu thin film interconnection based on LTCC substrates and the related process controls were studied. A high reliability "T" interface interconnection method for thin film magnetron sputtering Cr/Cu/Cr and Cr/Pd/Au composite membrane structure and its preparation method were proposed. The effects of the interface defect and roughness of LTCC-thin film, the control of residual photoresist quantity in BCB film through holes and the stress of metallization of dielectric membrane on the quality of thick thin film composite substrate were studied. The prepared 12-layer thick thin film mixed substrate(10 layers LTCC substrate, 2 layers of thin film wiring) 60 pieces, all passed the GJB2438 C. 2.7 film substrate evaluation standard. Compared to the LTCC substrate, the wiring density is increased by 4 times, size reduced by 40 %.
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