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90 SMT007 MAGAZINE I DECEMBER 2018 and Insulation Resistance. This test uses 20 cycles of various temperature and humidity levels to help drive as much moisture as pos- sible into the coating and see how effective it is at preventing ingress onto the surface of the assembly. I've mentioned six test methods, so that leaves just 247 more active test you could use to determine the reliability of your products. Did I mention I work for a test lab? Call me; let's talk. SMT007 Eric Camden is a lead investigator at Foresite Inc. To read past columns or contact Camden, click here. The main tests I would recommend for deter- mining baseline cleanliness levels and what effect they will have on end-use reliability are IC, SIR, and THB tests. However, there are a handful of others that are worth the time and money. Cross-sectioning per IPC-TM-650 2.1.1 is a great way to get a better understanding of the solder joint quality as well as the PC fabri- cation process. Knowing there is a good inter- metallic compound (IMC) will go a long way in determining if you will have possible issues with intermittent connectivity. A strong sol- der joint will also help with vibration issues in more severe operating environments. If you are planning to use conformal coat- ings, it is a good idea to test how resistant to moisture it is using TM-650 Moisture A study led by Chalmers University of Technology in Sweden has shown that carbon fibers can work as battery electrodes and store energy directly. This opens up new opportunities for structural batteries where the carbon fiber becomes part of the energy system. The use of this type of multifunctional material can contribute to a significant weight reduction in aircraft and vehicles of the future. Leif Asp, professor of material and computational mechanics at the university, headed up a multidisci- plinary group of researchers who recently published a study on how the microstructure of carbon fibers affects their electrochemical properties. Studying the micro- structure of different types of commercially available carbon fibers, the researchers discovered that carbon fibers with small and poorly oriented crystals have good electrochemical properties but a lower relative stiffness. If you compare this with carbon fibers that have large, highly oriented crystals, they have greater stiffness, but the electrochemical properties are too low for use in structural batteries. The researchers are collaborating with both the auto- motive and aviation industries. Asp explains that for the aviation industry, it may be necessary to increase the thickness of carbon fiber composites to compensate for the reduced stiffness of structural batteries. In turn, this would also increase their energy storage capacity. "The key is to optimize vehicles at the system level based on the weight, strength, stiffness, and electrochemical properties. That is something of a new way of thinking for the automotive sector, which is more used to optimizing individual components. Structural batteries may perhaps not become as effi - cient as traditional batteries, but since they have a structural load-bearing capability, very large gains can be made at the system level," Asp says. (Source: Chalmers University of Technology) Carbon Fiber Can Store Energy in the Body of a Vehicle Leif Asp

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