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82 PCB007 MAGAZINE I SEPTEMBER 2019 DLA's response to the previous three ques- tions is as follows: "The number of certified PWB suppliers today is basically adequate for the demand, but we continue to certify new suppliers as requested for basic items or specialty prod- ucts. PWB sites certified to MIL-PRF-31032 re- quire a lot more DLA management resources as compared to the historical MIL-PRF-55110 and MIL-PRF-50884. However, today, DLA has these resources." In fact, as of April 2019, two additional PWB suppliers were added to the DLA list of MIL- PRF-31032 certified sites. PCB007 Mike Hill is president of MIL-Q- Consulting LLC. He has been in the PWB fabrication industry for over 40 years. During that time, he par- ticipated in specification writing for both IPC and the military. Past em- ployers include ViaSystems, Colonial Circuits, and DDi. To read past columns or contact Hill, click here. these polymers tend to contort into twisted spirals when they join, severely impeding charge transport. It is possible to flatten conjugated polymers by apply- ing an enormous amount of pressure or by manipulating their molecular structure, but both techniques are very la- bor-intensive, said chemical and biomolecular engineer- ing professor Ying Diao, who led the study. "There really is no easy way to do this." Postdoctoral researcher Kyung Sun Park and gradu- ate student Justin Kwok noticed something while run- ning printing experiments and flow simulations in Diao's lab. Polymers go through two distinct phases of flow dur- ing printing. The first phase occurs when capillary action pulls on the polymer ink as it begins to evaporate, and the second phase is the result of the forc- es imposed by the printing blades and substrate. They also discovered a third phase, which occurs in between the two al- ready-defined phases, and shows the polymers being stretched into planar shapes. The polymers stretched and flattened in this third phase, but they also remain that way after precipitat- ing out of solution, making it possible to fine-tune printer settings to pro- duce conjugated polymers for use in new, faster biomedical devices and flexible electronics. (Source: UIUC) A research team led by chemical and biomolecular en- gineers from the University of Illinois at Urbana-Cham- paign (UIUC) have found a way to use polymer printing to stretch and flatten twisted molecules so that they conduct electricity better. The findings are published in Science Advances. Conjugated polymers are formed by the union of elec- tron-rich molecules along a backbone of alternating sin- gle and double chemical bonds. The conjunction allows electricity to travel very quickly through a polymer, mak- ing it highly desirable for use in electrical and optical ap- plications. This mode of transporting charges works so well that conjugated polymers are now poised to compete with silicon materials, the researchers said. However, Printing Flattens Polymers, Improving Electrical and Optical Properties

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