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32 DESIGN007 MAGAZINE I APRIL 2022 Feature Article by Tomas Chester CHESTER ELECTRONIC DESIGN Advances in technology have been clear to see within the component packaging indus- try, as the ball grid array (BGA) package sizes reduce from 1.0 mm pitch to 0.8 mm, 0.4 mm, and even beyond. However, while these improvements have occurred with component packages, it has become increasingly more difficult to break out and route the dense cir- cuitry associated with these parts. Currently, the high-density interconnect (HDI) method typically used for the breakout of such parts has been to create the smallest possible sub- tractive-etched traces with microvias to allow for connections and escapes on the innerlayers of your PCB. Now there are new fabrication processes that change how we can approach some of these layout difficulties. Additive and semi-addi- tive construction now allows us to get down below 0.075 mm trace and gap sizes easily and reliably, however, utilizing it brings its own series of challenges to the table. Before design- ers and engineers can start to use this tech- nology, we need to understand the difference between the standard subtractive fabrication method and these new additive fabrication methods, as well as their respective design requirements for trace impedance, and the signal integrity impact from routing traces closer together. Designing PCBs With Additive Traces

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