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September 2014 • The PCB Magazine 75 ROOT CAuSE OF FAILuRES IN PWB LAMINATION continues uting to delamination, it is important that a few simple precautions be instituted: • Innerlayer drying – Inner layers should be oven dried to remove absorbed moisture. Absorbed moisture in the inner layer can affect the curing properties of the prepreg. • (Innerlayer bake cycle) – 225°F in vertical racks with minimum 0.5" separation for 30 minutes – 110°C in vertical racks with minimum 1.2" separation Notes to consider: 1. If inner layers are baked horizontally in stacks of 1–2" (25–50 mm) extend time to at least 90 minutes. 2. Check with oxide supplier if using DMAB oxide reducer. Excessive exposure to heat may re-oxidize the reduced treatment. 3. Drying temperatures below 100°C are not effective in removing absorbed moisture from the layer. Summary Again, nothing is a replacement for process control and proper shop practices. And don't underestimate the detrimental effect of mois- ture. Even if all of the chemical processes and lamination cycles are optimized, moisture re- tention in the resin and laminate package will negate all of the good that has been done. PCB michael Carano is with omg electronic Chemicals, a devel- oper and provider of processes and materials for the electron- ics industry supply chain. to read past columns, or to con- tact the author, click here. a team of researchers at michigan state uni- versity has developed a new type of solar con- centrator that when placed over a window cre- ates solar energy while allowing people to ac- tually see through the window. the transparent luminescent solar concentrator and can be used on buildings, cell phones and any other device that has a clear surface. according to richard lunt of msu's College of engineering, the key word is "transparent." "no one wants to sit behind colored glass," said lunt, an assistant profes- sor of chemical engineering and materials science. "it makes for a very colorful en- vironment, like working in a disco. we take an approach where we actually make the luminescent active layer it- self transparent." the solar harvesting system uses small organ- ic molecules developed by lunt and his team to absorb specific non-visible wavelengths of sun- light. "we can tune these materials to pick up just the ultraviolet and the near infrared wavelengths that then 'glow' at another wavelength in the infrared," he said. the "glowing" infrared light is guided to the edge of the plastic where it is converted to elec- tricity by thin strips of photovoltaic solar cells. "because the materials do not absorb or emit light in the visible spectrum, they look excep- tionally transparent to the human eye," lunt said. one of the benefits of this new develop- ment is its flexibility. while the technology is at an early stage, it has the potential to be scaled to commercial or industrial applica- tions with an afford- able cost. Researchers Develop Transparent Solar Concentrator

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