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January 2015 • The PCB Design Magazine 53 TIPS EvERY DESIgNER SHOuLD KNOW continues Amit Bahl directs sales and marketing at Sierra Circuits, a PCB manufacturer in Sunnyvale, California. he can be reached by clicking here. design for manufacturing Crocus Technology's new magnetic logic unit- based (Mlu) solution can detect the position and shape of flexible two dimensional surfaces. Wear- able devices, curved panel displays, flexible solar panels, and, in the future, mobile phones will inte- grate flexible shape sensor foils. Crocus' magnetic sensors aim to provide an efficient solution for shape sensing in flexible surfaces and foils to overcome deficiencies occurring in other solu- tions, such as piezoelectric sensors. unlike other solutions, Crocus' Mlu sensors exhibit high sensitivity and di- rectional capabilities. This means that only a minimal number of Mlu sensors need to be embedded in flexible shape sensor foils. In its prototype, Crocus only uses 0.25 sensors per square centimeter, making its solution extremely cost-effective. In addition, Crocus' Mlu sensors offer advan- tages in low power consumption and high-speed detection. They provide strong signals without ac- tive components. Crocus' 20cm x 20cm prototype consumes less than 10mA during the sensing cycle that lasts less than 1ms. "Crocus has created a new IP-based on magnet- ic sensors for flexible surface position detection. This enables equipment makers to gain in the added per- formance of flexible shape devices, while reducing costs," said Bertrand Cambou, chairman and Ceo of Crocus Technology. As flexible displays are light, thin and unbreakable, they are expected to replace conventional displays. According to Cro- cus' press release the market for flexible displays is expected to reach uSD $3.89 billion by 2020. Sensors Enable Further Flexing of Flex Displays ple. In any event, unless a board involves a BGA with a very tight pitch or one with a great many connections, there's seldom any need for a drill size smaller than 8 mils. Many designers don't realize the soldermask is what determines design rules, not copper-to- copper or pad-to-pad minimums, Albers points out. "The smallest spoke of a solder mask is 4 mils, period. You can't go below that whether or not you use standard LPI soldermask or laser- defined soldermask or there will be registration issues," says Albers. "You can decide to use a laser-defined solder mask to provide the bet- ter precision than LPI, which is unavoidable if there's a BGA with tight spacing, but that costs more. Getting the most for your money should be the objective when you need production quantities. However, unless you really know fabrication, collaborate with your manufacturer before you design." Albers notes that engineers often pick BGAs with the finest pitch available, figuring the smallest packages will conserve board territory. However, the breakout for larger packages in many cases will actually result in less area con- sumed. Package selection for complex devices ought to involve both the circuit designer and the PCB layout designer. "As a rule of thumb, to estimate the number of layers a board will include, count the number of ball rows in the most complex BGA. You'll need a power plane per supply value for the part and associated ground planes. That pack- age guides the project," Albers says. Albers places and routes the power section of designs first, keeping most of the active de- vices on one side of the board and discretes on the other with assembly in mind. He can almost always accomplish a design without turning to fine trace and space widths. Albers' advice in a nutshell? Think big. PCBDESIgN

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