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74 DESIGN007 MAGAZINE I SEPTEMBER 2023 Article by Anaya Vardya AMERICAN STANDARD CIRCUITS ere has always been pressure to reduce line and space as we have seen the bleeding edge technology go from 8 to 5 mils and then to 3 mils. e difference between then and now is that the prior advancements, for the most part, used the same processes, chem- istry, and equipment going from 8 mils to 3 mils. But going from 3-mil to sub 1-mil trace and space is a quantum leap in printed circuit board (PCB) technology that requires a whole new set of processes and materials. High density interconnect (HDI, the pre- decessor of UHDI) deals with line width and space, but primarily employs via structures to increase density. In broad terms, HDI printed circuit boards are defined as PCBs with one or more of the following via structures: micro- A Primer on UHDI vias, stacked and/or staggered microvias, bur- ied and blind vias, and all with sequential lami- nation cycles. Printed circuit board technol- ogy has been evolving with changing technol- ogy that demands smaller and faster features. HDI boards allow smaller vias, pads, lines and spaces—in other words, higher density. is increased density also allows a reduction in the number of layers and a smaller footprint. For example, one HDI board can house the functionality of multiple standard technology PCBs. Conventional state-of-the-art technol- ogy has been stuck at the 3-mil line and space capability for the longest time, but that is just not good enough to meet the increasingly tighter real estate constraints of today's prod- ucts. at is where Ultra HDI comes in.

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