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40 DESIGN007 MAGAZINE I JANUARY 2021 Feature by Cherie Litson, CID+, MIT LITSON1 CONSULTING There are so many ways to do a layer stackup for your PCB, and lots of great articles on how to structure them. You can do an online search and I'm sure you'll find something that will work just right for your design. Not a bad start, but pretty soon it gets con- fusing. There are so many options! And how do you know how many layers you're going to need anyway? Let's see if we can simplify the number of layers concept a little bit so that you can fine tune your search. How many layers do you need to start with? First, what restrictions and features do you have? Part area: The number, size, and type of your parts will play a large role in influencing the number of layers you will need. You will need the complete part area. The part area must include the "courtyard" area around the part. If you have a database for your parts, it's a good idea to incorporate this number in the attributes so you can get a quick total from the BOM. (Otherwise, it's a bit time-consuming to find this.) Layer Stackup, Short and Sweet If you have any components with a pin spacing of 0.5 mm (.020") or less, you're into HDI land. Depending on how many pins are on these small parts and the breakout pattern you'll need, you'll be using blind and buried vias which require at least a four-layer board and probably more. There are some new tech- niques and fabrication processes that are com- Figure 1: Don't forget to include the courtyard area around your part.

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