PCB007 Magazine

PCB-June2015

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52 The PCB Magazine • June 2015 Consumer electronics, wearable devices, the Internet of Things, medical devices, auto- motive, and military electronics markets are driving flexible circuits into increasingly more products. The push for smaller, cheaper, and more capable devices in each of these industries demands flexible circuits. This can mainly be at- tributed to the flexible circuits' ability to allevi- ate some of the packaging difficulties resulting from moving to smaller devices—flexible cir- cuits allow for more packaging flexibility, both literally and figuratively. Trends in Flexible Circuit Processing In order to reduce costs while improving capabilities (generally in the form of more pro- cessing power, higher clock speeds, more so- phisticated communications technologies, and lower power usage), the industry is moving to more complex board stack-ups, more compli- cated, smaller, and fine-featured shapes, and a higher usage of small blind and buried micro- vias and ever-thinner materials. by Patrick Riechel ESI Staying Current: High-Speed uV Laser Micromachining and Flex Circuit trends Although double-sided flexible circuits are still the most typical construction, complex multilayer stack-ups and rigid-flexible circuits are becoming more common. These multilayer constructions allow the designer to make the flexible circuit more functional. Not only do they allow for more signals to pass through the circuit and the robust placement of chips, they also enable the designer to implement electro- magnetic shielding to prevent noisy high-speed signals from interfering with sensitive signals both inside and outside of the product. Another benefit is enhanced impedance control for both high-speed and RF communications signals. Multilayer constructions such as these come with unique challenges for via processing. Given the typical use of flexible circuits to fit into small and difficult spaces and the trend toward smaller and thinner end-user devices, it is not surprising that the shapes and sizes of flexible circuits are becoming more complex, fine-featured, and smaller. These shapes and siz- es are beginning to drive a need for more accu- rate and fine-grained cutting methods for both circuit and coverlay material. While simple through vias are still the most common method of connecting signals from FeAtuRe

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