Issue link: https://iconnect007.uberflip.com/i/1481368
34 DESIGN007 MAGAZINE I OCTOBER 2022 process can typically provide features as small as 30 microns in highly specialized facilities that are running extremely high-volume man- ufacturing. is technology is commonly seen in our smartphones. Averatek's A-SAP begins with a much thin- ner electroless copper, typically 0.2 micron and this copper thickness, or thinness if you will, enables the fabricator to produce much finer feature sizes. e technology is capable of traces and spaces as small as 1 micron if the fabricator has advanced imaging equip- ment. Typically, PCB fabricators have equip- ment that can image traces to 12.5 mm today. ere are also signal integrity benefits to this process. Because the base copper is so thin, there is minimal impact on the trace sidewalls, and greater control to line width resulting in impedance control tolerance improvements. One other difference between the mSAP and A-SAP technologies is in the ratio of trace height to trace width. mSAP processes allow a 1:1 ratio of height to width and A-SAP traces can be produced with aspect ratio of 2:1 or greater. For example, a 25-micron wide trace could be 40 microns tall. is has gotten a lot of attention from a signal integrity perspective. Q: How is designing in the ultra-HDI arena dif- ferent from designing a typical PCB, or even an HDI board? A: I sometimes worry that designers will think they must learn a whole new way to design if they want to work with ultra HDI designs. I believe it is not that different than when a designer first learns to design with flex materi- als. Most things are the same as designing with rigid and once you learn the specific items that are different and why, designing with a new technology becomes much easier. at said, this does give the industry the opportunity to reimagine how PCB design is done. In general, the constraints have been at 75-micron line and space for so long that, col- lectively, we have learned to work around that with blind and buried vias, stacked and stag- gered microvias, an increasing number of lam- ination cycles to create enough space to route out tight pitch BGAs, etc. e SAP processes and finer line widths can free up valuable real estate and help to simplify the design and reset the technology curve. ere are a couple of different ways to approach a design with ultra HDI and I think the approach varies according to a designer's particular priorities. For some, the priority is overall miniaturization, which may be in size, or overall thickness. For others, a top prior- ity is via reliability and the focus is on reduc- ing lamination cycles or even using space to increase hole size and move from an HDI con- struction to a through-via construction. Circling back to the flex comparison, I want to be sure to mention that SAP processes can be built with a variety of materials including flexible materials and that not all layers in a PCB design need to be done with SAP. It is a layer-by-layer selection, and it is common that power and ground layers, or any layer with only 75 micron or greater feature sizes will be built with subtractive etch process. Q: What are some of the benefits of UHDI? A: I think the primary benefits are: • Dramatic size and weight reduction over current subtractive etch processing. PCBs can be made much smaller and thinner. • Improved reliability: is could be f rom reduced layer count, reduced lamination cycles, reduced dependence on microvias, etc. • Improved signal integrity: As I mentioned, higher aspect ratio of height to width, which opens up several things to PCB designers, and tighter control on feature sizes improves impedance control. • Reduced costs: is one may seem coun-