Effect of Temperature Cycling on IMC Growth and Solder Joint Strength of SAC305 Solder Alloy and Low Silver Alloy REL61

This work deals with the comparison of the standard SAC305 (Sn 96.5 %; Ag 3 %; Cu 0.5 %) solder alloy with melting temperature between 217 - 220 °C and an alternative alloy REL61 (SnBiAgCu) with lower silver content and melting temperature in the range of 208 - 215 °C in terms of IMC layer growth during thermal cycling and its effect on the shear strength of the solder joints. The test PCBs were soldered using two different temperature profiles and the temperature cycling was performed under two different conditions. No negative effect of REL61 solder alloy on the growth of the IMC layer under thermal stress and on the subsequent shear strength of the solder joint was found. From this point of view, the REL61 solder alloy can be used as a replacement for the SAC305 solder alloy.

Smart Glass Coatings for Innovative BIPV Solutions

The glossy appearance of the cover glass of a photovoltaic module is mainly responsible for giving the module a mirroring effect, which is often disturbing in the case of building integrated photovoltaic (BIPV) façade applications. In this work, an innovative approach is presented to reduce the glare of BIPV modules by applying surface coatings to the front glass of the module. Three different glass coating technologies, applied on the outer surface of the photovoltaic module, were investigated: inkjet printing, screen printing, and sol-gel spray coating. The coatings, applied by these technologies in three different colours (grey, anthracite, and terracotta), were characterized with respect to their adhesion, light transmission, and reflection. Their chemical and physical stability after stress impact (condensed water resistance and chemical resistance against acids and salt-fog) was also investigated. The durability of these coatings was further evaluated after performing environmental simulations with artificial sunlight (xenon weathering) on coated glass. Additionally, accelerated aging tests (damp-heat testing, temperature cycling) were performed on the test modules to assess their performance stability. For those coatings, where no stress-induced changes in colour or the optical appearance of the module surface were detected, the potential for the architectural integration of the modules into building facades is high. A minimum glare of less than 0.1% of the specular reflection could be achieved. On the basis of the results of the optical characterization and the durability tests, grey screen-printed BIPV solar modules were installed in a demonstrator test façade. The high electrical performance, resulting in only a 10–11% performance decrease compared to the noncoated reference modules, perfectly showed the suitability of screen-printing in future applications for coloured and glare-reduced BIPV installations.

Impact of Graphite Materials on the Lifetime of NMC811/Graphite Pouch Cells: Part I. Material Properties, ARC Safety Tests, Gas Generation, and Room Temperature Cycling

The impact of graphite materials on capacity retention in Li-ion cells is important to understand since Li inventory loss due to SEI formation, and cross-talk reactions between the positive and negative electrodes, are important cell failure mechanisms in Li-ion cells. Here, we investigate the impact of five graphite materials from reputable suppliers on the performance of NMC811/graphite cells. We show that natural graphites (NG) here have a mixture of 3R and 2H phases, while artificial graphites (AG) were 2H only. We find that there are differences between the N2 BET surface area and the electrochemically-accessible area where redox reactions can take place and it is the latter that is most important when optimizing graphite-containing cells. Part I of this 2-part series investigates physical and electrochemical differences between the graphite materials of interest here, as well as room temperature cycling to probe improvements in capacity retention. We demonstrate that advanced AG materials with small accessible surface areas can improve safety, 1st cycle efficiency (FCE) and long-term cycling. Part II of this work examines elevated temperature cycling, cell swelling, and makes lifetime predictions for the best NMC811/graphite cells.

A cryo-TSEM with temperature cycling capability allows deep sublimation of ice to uncover fine structures in thick cells

The scanning electron microscope (SEM) has been reassembled into a new type of cryo-electron microscope (cryo-TSEM) by installing a new cryo-transfer holder and anti-contamination trap, which allowed simultaneous acquisition of both transmission images (STEM images) and surface images (SEM images) in the frozen state. The ultimate temperatures of the holder and the trap reached − 190 °C and − 210 °C, respectively, by applying a liquid nitrogen slush. The STEM images at 30 kV were comparable to, or superior to, the images acquired with conventional transmission electron microscope (100 kV TEM) in contrast and sharpness. The unroofing method was used to observe membrane cytoskeletons instead of the frozen section and the FIB methods. Deep sublimation of ice surrounding unroofed cells by regulating temperature enabled to emerge intracellular fine structures in thick frozen cells. Hence, fine structures in the vicinity of the cell membrane such as the cytoskeleton, polyribosome chains and endoplasmic reticulum (ER) became visible. The ER was distributed as a wide, flat structure beneath the cell membrane, forming a large spatial network with tubular ER.

Impacts of Substrate Thinning on FPGA Performance and Reliability

Global thinning of integrated circuits is a technique that enables backside failure analysis and radiation testing. Prior work also shows increased thresholds for single-event latchup and upset in thinned devices. We present impacts of global thinning on device performance and reliability of 28 nm node field programmable gate arrays (FPGA). Devices are thinned to values of 50, 10, and 3 microns using a micromachining and polishing method. Lattice damage, in the form of dislocations, extend about 1 micron below the machined surface. The damage layer is removed after polishing with colloidal SiO2 slurry. We create a 2D finite-element model with liner elasticity equations and flip-chip packaged device geometry to show that thinning increases compressive global stress in the Si, while C4 bumps increase stress locally. Measurements of stress using Raman spectroscopy qualitatively agree with our stress model but also reveal the need for more complex structural models to account for nonlinear effects occurring in devices thinned to 3 microns and after temperature cycling to 125°C. Thermal imaging shows that increased local heating occurs with increased thinning but the maximum temperature difference across the 3-micron die is less than 2°C. Ring oscillators (ROs) programmed throughout the FPGA fabric slow about 0.5% after thinning compared to full thickness values. Temperature cycling the devices to 125°C further decreases RO frequency about 0.5%, which we attribute to stress changes in the Si.

Temperature Cycling Study of Aerosol-Jet Printed Conductive Silver Traces in Printed Electronics

Aerosol-Jet Printing (AJP) provides a new method for electronic component manufacturing. Understanding the reliability of electronics printed using the AJP process is essential to take full advantage of this technology and realize its industrial potential. In the current study, we have designed and tested AJP printed samples and conducted failure analysis of those samples that have exhibited early failures. Failures first occurred in the short traces that connect the main traces to the silver pads, due to local stress-raisers caused by local geometric features in the printing geometry. Thermal-Mechanical Finite-Element-Modeling (FEM) has been performed to analyze the cyclic history of thermo-mechanical stress distribution and plastic strain distribution.