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Design007-Aug2018

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34 DESIGN007 MAGAZINE I AUGUST 2018 Feature by Christian Keller ALTIUM PCB developers are deluged with new chal- lenges caused by increasing density and smaller components. Ball grid arrays (BGAs) create particular challenges during layout, with hundreds of connections in just a few square centimeters. Fortunately, designers now have options for addressing these issues. Fanout and Escape Routing Because of the density and distance from the connection points, only the two outermost rows of a BGA can be connected directly to surface circuit traces. All other terminals of the BGA cannot be connected in a direct path on the surface. Fanout and escape routing is integrated in many PCB design systems to enable further connections. In fanout and escape routing, the two outermost rows, and all other rows of a BGA, are automatically connected to the cen- ter of the terminals via a short circuit trace that is executed at a 45° angle. This provides a blind via that forms a direct connection to the next signal layer. Routing can be executed on the next signal layer. Using via-in-pad eliminates the need for the additional trace to the center of the connec- tions, thereby creating additional space for circuit traces. Therefore, with via-in-pad, the through contact can be placed directly at the terminal of the BGA. Figure 1: BGA with classic fanout routing of all the electrical connections.

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