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March 2015 • The PCB Magazine 75 it is time to produce and use a new phototool. Even with the proper exposure technique and high quality phototool, LPI ink may still remain in the vias due to poor developing. Even if one assumes that the ink in the via is not par- tially exposed (due to low D-max) or over dry (tack dry issues), improper control of the de- veloping operation reduces the effectiveness in removing ink from the vias. With respect to de- veloping, the greatest difficulty is encountered in removing the unexposed ink from small di- ameter vias. The prerequisites for good develop- ing then are: • Sufficient amount of spray nozzles in the developer chamber • Combination of different spraying angles and spray patterns • Implementation of low-pressure, high-volume nozzles • Implementation of permanent wetting of squeeze rollers • Use of high performance blowers (needed for dry holes) • Maintenance of sodium carbonate levels in developer between 0.9–1.1%, by weight If one follows these key items, the develo- ping quality will prove to be excellent. 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. Scientists have known how to draw thin fi- bers from bulk materials for decades. But a new approach to that old method, developed by researchers at MIT, could lead to a whole new way of making high-quality fiber-based electron- ic devices. The idea grew out of a long-term research ef- fort to develop multifunctional fibers that incor- porate different materials into a single long func- tional strand. until now, those long strands could only be created by arranging the materials in a large block or cylinder called a preform, which is then heated and stretched to create a thin fiber that is drastically smaller in diameter, but retains the same composition. now, for the first time, fibers created through this method can have a composition that's com - pletely different from that of the starting mate- rials—an advance that lead researcher Yoel fink refers to as a kind of "alchemy," turning inex- pensive and abundant materials into high-value ones. The new findings are described in a paper in the journal nature Communications co-au- thored by graduate student Chong hou, and six others at MIT and in Singapore. The fibers are made from aluminum metal and silica glass, abundant low cost materials, which are commonly used to make windows and win - dow frames. The aluminum metal and silica glass react chemically as they are heated and drawn, producing a fiber with a core of pure, crystalline silicon—the raw material of computer chips and solar cells—and a coating of silica. Making High-quality Fiber- based Electronic Devices trouble in your tank MORE PESky SOLDERMASk PROBLEMS: PLUGGED VIA LEADING TO SkIP PLATING continues