Practical Blind and Buried Vias? - Page 1
Forum section: electronics / general

author: rx8pilot
author_rank: Super Contributor
timestamp: February 08, 2018, 07:27:43 pm
content: For those that understand the details of PCB fabrication....this is for you.As my layouts need to be smaller and smaller with parts on both sides - blind and buried vias are not just an interesting option but rather the ONLY option.Trying to get an overview of what is possible first, then create a sample layout and send it to a few of my typical fabs to get DFM feedback from them. While I am aware that blind and buried vias rapidly increase cost - I am trying to build some understanding of what is easy, what is possible but difficult, and what is just stupid and don't ask for it.Kind of like learning not to ask a machinist to drill a square hole.Simple Example: 4 layerEagle naming is weird - 1-2-15-16 are the layer namesThrough 1-16 - standard, easyBlind 1-2 - seems standardBlind 1-15 - ?? Not sure this won't raise flagsBlind 16-15 - seems standardBlind 16-2 - ?? Not sure this won't raise flagsBuried 2-15 - seems standardAre the blind vias from layer 1-15 (going through layer 2) something to avoid or is it no big deal?I know that someone somewhere can fabricate any stack that I dream of, but the goal is to keep it in the realm of a typical pcb house. Does not need to be the bottom of the barrel or the super fancy aerospace exotic.

author: Someone
author_rank: Super Contributor
timestamp: February 08, 2018, 08:59:08 pm
content: It really depends on the specific stackup process used by the specific fab line, in the simplest case:a 4 layer board can be laminated both sides over a double sided core, orbe a pair of double sided units sandwiched togetherFor one of those buried vias are cheap and blind vias expensive, and the reverse for the other. You optimise cost when you follow the "standard" flow for the fab as closely as possible but the only people who can answer that are the people running your lines. As layer count grows it gets much more complicated and there may no longer be a default flow so you can get more choice in what you want without it costing "more" since its all one off pricing at that point anyway.

author: rx8pilot
author_rank: Super Contributor
timestamp: February 08, 2018, 09:44:07 pm
content: Thank you....Perhaps I should just send some emails with that graphic to 3-4 houses and see what kind of variety I get in return. It would be nice to get a stack that is reasonable for a variety of houses so I do not get trapped with only 1-2 vendors that can do it The Chinese vendors are all going on the big holiday so I will start with the USA options.

author: cgroen
author_rank: Unknown
timestamp: February 09, 2018, 09:22:35 am
content: rx8pilot,you could also have a look at eurocircuits, they have a short explanation of buried/blind vias here:https://www.eurocircuits.com/blog/blind-and-buried-vias/

author: Ice-Tea
author_rank: Super Contributor
timestamp: February 09, 2018, 09:27:57 am
content: Suggest you check this:http://www.we-online.com/web/en/index.php/download/media/04_leiterplatte/2017_2/dg_poster_2/170125_WE_DesignGuide_HDI_Poster_EN_web.pdfAnd perhaps some more WE guidelines

author: rx8pilot
author_rank: Super Contributor
timestamp: February 09, 2018, 06:41:10 pm
content: Quote from: cgroen on February 09, 2018, 09:22:35 amThat is an EXCELLENT article. Does a great job if explaining what is practical and what is impossible. Thanks for posting that.It looks like my example would indeed be in the impossible category.

author: Someone
author_rank: Super Contributor
timestamp: February 09, 2018, 10:32:01 pm
content: Quote from: rx8pilot on February 09, 2018, 06:41:10 pmImpossible for them, but I've had boards made that violate their rules with several other fabs. Like above every fab will offer different possibilities and trying to find a common set of rules will reduce you to an extremely limited subset of whats possible.