Most common 4 and 6 layers stackups? - Page 1
Forum section: electronics / projects

author: ricko_uk
author_rank: Super Contributor
timestamp: May 01, 2022, 04:19:04 pm
content: Hi,whenever the PCB stackup/build becomes relevant (i.e. controlled impedance) I always check which manufacturer the client wants to use and check with them the options and ask them to give me the values for differential/controlled impedance tracks/gaps. For precision projects that I guess will always remain the best approach...But there must some "standard" or perhaps rather than standard more "common" stackups and materials which across the industry, for cost and manufacturing optimization, most manufacturers tent to revert to. Perhaps dictated by the most common materials supplied by the largest suppliers worldwide.So I was wondering if anybody ever did any such "research"... and if not if there are some 4 and 6 layers stackups (materials, thicknesses etc) which are safer to use across manufacturers?Thank you

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 01, 2022, 04:44:42 pm
content: The ~30 mil core with build-up 7-10 mil prepreg stackup is more common, AFAIK. JLC's 5 mil (or less, whatever it is?) prepreg is a somewhat less common / newer sort of thing. So, I would target the first one, and make it clear in the notes that it's the stackup expected, and note critical nets if applicable.Similarly for 6 layer, I think 7 mil prepreg is the usual go-to (or was), so whatever that stackup comes out to.Helps to have a txt file in the ZIP making this clear, as well as on the drill drawing or whatever. I usually start with something like:Code:Board Details-----------------Number of Layers: 4Board Thickness: 0.062 inBoard Material: FR-4, Tg >= 140CBoard Size X: 4.00 inBoard Size Y: 4.00 inCopper Weight Outer: 1 ozCopper Weight Inner: N/ASoldermask Color: GreenSilkscreen Color: WhitePlating: Lead-Free HASLNumber of Sides requiring Assembly: 2Approximate Number of Pads, Vias, Holes: 1337Approximate Number of SMT Components, Top: 69Approximate Number of SMT Components, Bottom: 0Approximate Number of Thru-Hole Components: 42Approximate Number of BGA/QFN/Leadless Components: 1Blind & Buried Vias: 0And add any controlled impedance notes at the bottom say, or recommended/required stackup with the geometry specs there. Can show the stackup on the drill drawing with a table, or graphically.You can always custom order, of course, at the expense of increased cost and lead time. It's not too bad, like, I've ordered a 20-20-20 mil stackup from PCBCART I think it was, for a high power inverter (hence the increased spacing), which was like $250 for, 4 or 5, or was it 10, I forget?And that's just protos, the incremental cost is basically negligible once you're in production.Tim

author: eugene
author_rank: Frequent Contributor
timestamp: May 01, 2022, 05:10:54 pm
content: Quote from: T3sl4co1l on May 01, 2022, 04:44:42 pmI agree and have always included a readme.txt file or a mechanical drawing calling out any requirements, usually both. But I am not sure that JLCPCB looks at them. If it's not specified by the check boxes on the web page when ordering, then I wouldn't count on getting it.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 01, 2022, 06:48:27 pm
content: Yeah, for any budget proto service, you get what they give you. Don't expect more than baseline service, divergence from their standard stackups, etc.Tim

author: ricko_uk
author_rank: Super Contributor
timestamp: May 01, 2022, 07:11:45 pm
content: Thank you both