Design Talk: January 2010
Stop Compromising Your PCB Layout
By David Donaldson, W. L. Gore & Associates, www.gore.com 
As electronic devices are getting smaller and as consumers are demanding more features, designing printed circuit boards (PCBs) is becoming increasingly complex, not to mention that any finished design must face both performance testing and testing for compliance with Federal Communications Commission rules and other codes.
Many design engineers start by considering shielding requirements, doing such things as identifying the noisy components and placing them as far away from sensitive ones so as to reduce potential interference; however, they also realize that if the product fails in the testing lab, they will have to add cans to the board to provide shielding. To allow space for shielding cans, they may have to group the largest components together to make the best use of these cans. This reactive mindset translates to making the design conform to the shape of the shielding can and designing the board based on shielding requirements rather than seeking an optimal design that maximizes space usage and functionality.
Thermoformed, board-level shields permit design engineers to place components and circuits on a PCB based on function as opposed to the need to conform to the predefined geometry of the shield. Engineers can design the board based on circuit and component function without the constraints imposed by the shape of traditional shielding cans. Using a single thermoformed shield provides many specific advantages, all of which result in increased flexibility in board design, integration, and performance.
Board Design Flexibility
Today’s consumers want electronic devices in all shapes and sizes, which can dictate the enclosure design and the board shape. Stock components and cans are generally square or rectangular, and placing square cans on irregular boards has a significant impact on the engineer’s ability to place components on the board. Thermoformed shields can be shaped to fit any board, regardless of its geometry, without increasing the complexity of manufacturing the shield itself. Design engineers who opt for thermoformed shields at the outset of a design project can focus on effective board design without being limited by the shape and construction of their EMI shields
Additionally, thermoformed shields minimize the amount of space needed to shield individual areas. Rather than having multiple cans on a board, each of which needs its own trace to connect to the ground plane, a PCB only needs one thermoformed, multi-cavity shield with a single row of solder spheres to connect the individual cavities to the ground plane. For example, if an engineer plans to use individual cans to separate two cavities, each can needs its own ground trace with space between them. With a thermoformed, multi-cavity shield, only a single ground trace between the cavities is needed.
The design flexibility of thermoformed shields enables implementation of other necessary features such as mouse holes to avoid coupling, entry points for cables and connectors, and air perforations to facilitate cooling. This allows components and circuits to be placed in their optimum location without first considering shielding requirements.
Thermoformed shields are an innovative EMI shielding solution that maximize flexibility related to board design. Design engineers no longer need to compromise the layout of their printed circuit board. By selected this shielding type up front, they can create their ideal layout and have the EMI solution conform to this design.
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