ИССЛЕДОВАНИЕ ПРОЦЕССОВ ПАЙКИ КРЕМНИЕВЫХ КРИСТАЛЛОВ МОЩНЫХ ТРАНЗИСТОРОВ В ИХ КОРПУСА

The aim of this work is to find out the possibility to reduce the laboriousness and cost of high−power silicon transistors manufacturing with retention of their low thermal resistance. To this end we carried out experimental research of replacement soldering silicon chips in the housing transistors of Au—Si solder for lead−silver solder and some other solders. This will reduce the consumption of gold and increase the productivity of the high−power transistors silicon chips installation due to the collective technology application. At the same time it was found that different treatments of the reverse side of the silicon wafer and their thinning influence the thermal resistance. To improve the quality of soldering we used preliminary metallization of the reverse side of the silicon wafer — Ti—Ni coating. We performed experimental evaluation of the influence of the outer layer materials of the housings and the back side metallization of the chips. When one utilizes soldering silicon chips with lead−silver solder, the housing with a nickel outer layer has the advantage, rather than the gold−plated one, as far as the resulting thermal resistance was lower and the absence of gold made the technology cheaper. We obtained a thermal resistance of 0.6 K/W for a chip area of 24 mm2.Качество монтажа кристаллов транзисторов в их корпусах характеризуется тепловым сопротивлением собранного транзистора. Достижение низкого значения теплового сопротивления особенно важно для мощных кремниевых транзисторов. Существует несколько способов монтажа кристаллов мощных кремниевых транзисторов в корпуса приборов с помощью пайки, в частности, эвтектикой золото—кремний, свинцовым припоем ПСр−2,5 или бессвинцовыми припоями, например сплавом золото—олово. Рассмотрена возможность сокращения трудоемкости и стоимости изготовления кремниевых транзисторов при сохранении низкого теплового сопротивления. Проведено экспериментальное исследование замены пайки кристаллов эвтектикой золото—кремний пайкой главным образом преформой из припоя ПСр−2,5, а также некоторыми паяльными пастами. Это дает экономию золота и увеличение производительности операции монтажа кристаллов за счет использования групповой технологии пайки. Одновременно исследовано влияние на значение теплового сопротивления способа обработки обратной стороны кристаллов и их утонения. Для повышения качества пайки применена предварительная металлизация обратной стороны кремниевой пластины покрытием Ti—Ni, что значительно облегчило процесс пайки. Экспериментальная работа по переходу на пайку свинцово−серебряными припоями проведена на кристаллах мощного серийного транзистора КТ−866, монтируемых в корпуса КТ−57. При площади кристалла 24 мм2 тепловое сопротивление транзистора с утоненным кристаллом составило примерно 0,6 К/Вт, что ниже значения для серийно выпускаемых транзисторов. Значение теплового сопротивления транзистора с не утоненным кристаллом составило примерно 0,8 К/Вт, что ниже предельно допустимого для данного прибора значения 1,0 К/Вт

Model Convolution: A Computational Approach to Digital Image Interpretation

Digital fluorescence microscopy is commonly used to track individual proteins and their dynamics in living cells. However, extracting molecule-specific information from fluorescence images is often limited by the noise and blur intrinsic to the cell and the imaging system. Here we discuss a method called “model-convolution,” which uses experimentally measured noise and blur to simulate the process of imaging fluorescent proteins whose spatial distribution cannot be resolved. We then compare model-convolution to the more standard approach of experimental deconvolution. In some circumstances, standard experimental deconvolution approaches fail to yield the correct underlying fluorophore distribution. In these situations, model-convolution removes the uncertainty associated with deconvolution and therefore allows direct statistical comparison of experimental and theoretical data. Thus, if there are structural constraints on molecular organization, the model-convolution method better utilizes information gathered via fluorescence microscopy, and naturally integrates experiment and theory

The Actin-Binding Protein Capulet Genetically Interacts with the Microtubule Motor Kinesin to Maintain Neuronal Dendrite Homeostasis

BACKGROUND: Neurons require precise cytoskeletal regulation within neurites, containing microtubule tracks for cargo transport in axons and dendrites or within synapses containing organized actin. Due to the unique architecture and specialized function of neurons, neurons are particularly susceptible to perturbation of the cytoskeleton. Numerous actin-binding proteins help maintain proper cytoskeletal regulation. METHODOLOGY/PRINCIPAL FINDINGS: From a Drosophila forward genetic screen, we identified a mutation in capulet--encoding a conserved actin-binding protein--that causes abnormal aggregates of actin within dendrites. Through interaction studies, we demonstrate that simultaneous genetic inactivation of capulet and kinesin heavy chain, a microtubule motor protein, produces elongate cofilin-actin rods within dendrites but not axons. These rods resemble actin-rich structures induced in both mammalian neurodegenerative and Drosophila Alzheimer's models, but have not previously been identified by loss of function mutations in vivo. We further demonstrate that mitochondria, which are transported by Kinesin, have impaired distribution along dendrites in a capulet mutant. While Capulet and Cofilin may biochemically cooperate in certain circumstances, in neuronal dendrites they genetically antagonize each other. CONCLUSIONS/SIGNIFICANCE: The present study is the first molecularly defined loss of function demonstration of actin-cofilin rods in vivo. This study suggests that simultaneous, seemingly minor perturbations in neuronal dendrites can synergize producing severe abnormalities affecting actin, microtubules and mitochondria/energy availability in dendrites. Additionally, as >90% of Alzheimer's and Parkinson's cases are sporadic this study suggests mechanisms by which multiple mutations together may contribute to neurodegeneration instead of reliance on single mutations to produce disease

Study of silicon chip soldering in high-power transistor housing

The aim of this work is to study the possibility of reducing the labor consumption and cost of high-power silicon transistor manufacturing without compromise in transistor low thermal resistance. To this end we experimentally explored replacing Au-Si solder with lead-silver solder or other solders for silicon chip soldering in transistor housings. This will reduce gold consumption and increase the efficiency of high-power transistor silicon chip installation due to the use of batch soldering technology. We also studied the effect of different silicon wafer back side treatment and thinning methods on the thermal resistance of the transistors. To improve the soldering quality we applied preliminary Ti–Ni metallization of the reverse side of the silicon wafer. We experimentally assessed the effect of outer housing layer materials and back side chip metallization. For lead-silver soldering of silicon chips, the best housing is that with a nickel outer layer rather than with a gold-plated one, because the resultant thermal resistance is lower and the absence of gold makes the technology cheaper. We obtained a 0.6 K/W thermal resistance for a 24 mm2 chip area

Sharks' teeth and dunes

No abstract available