FEDEVEL
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Anatoliy , 10-12-2019, 04:08 AM

Hello,
While routing decoupling caps under an annoying BGA, i wondered- why can't i use Blind-Vias-In-Pad...
after a moment of research, i stumbled across this article by cadence- and i now wonder why not use the methods mentioned there, and why can i not see this option in altium?

and if Common experience claims that this is not a good solution' can you please link me some bga decoupling to try and understand the pattern/topology?

Edit- Noticed adding a link did not work, here

Anatoliy , 10-12-2019, 04:26 AM

welp, adding link does not work... lets try again https://linkshrink.pro/glmVleDk

Paul van Avesaath , 10-15-2019, 02:51 AM

hmm well I never needed it so i can only guess here..

i think the reason for it not being a valid solution or not recommened via to use in a pad is that well... hmmm... eehmmmm.. i have absolutly no idea why you should not use a blind via in a pad..

btw you link seems a but dodgy so i will not open it. srry...

Mihai , 10-15-2019, 03:49 AM

Hi,

I think it may have to do with the soldering. From what I have seen, while soldering on a board which had via-in pad, the solder paste was travelling in the via-in-pad from top to bottom. Also I saw that the components tend to be misaligned due to this issue. But this is what I have seen while assembling a board with via-in-pad

Vlad

Paul van Avesaath , 10-15-2019, 03:57 AM

ah might be so.. I am so used to having plugged and plated via's that i did not even concider this.

Anatoliy , 10-15-2019, 10:38 AM

here is the same link but from the official site- https://community.cadence.com/CSShar...ing_5myths.pdf
if you want to search for it yourself, it is called "Five Via-In-Pad Myths"

I am wondering why there is no way to a blind via in pad in altium, and if there is, then how?
it could make BGA decoupling much easier, with the regular dog-bone, TH via open side on top, and capped side on bottom - allowing dense 0402 decoupling while meeting design guide requirements and making manufacturing easier.

Paul van Avesaath , 10-15-2019, 11:15 PM

just a quick way but maybe more cumbersome than other ways.. just make a top via to layer x that you want. and copy and paste it in you pad. if altium does not let you select it..
you may need to change some rule settings for your DRC.
also did you set up your via stacks? then you should be able too cycle through them with " * "

Anatoliy , 10-16-2019, 02:36 AM

I did set up my via stacks, but what i mean is, that i see no way to make a complete TH via, covered on one/both sides, in altium;
like in example b in the document;
do you have any suggestion for alternatives?

robertferanec , 10-16-2019, 04:28 AM

- from the text it looks to me like you are looking for filled VIAs. I am not PCB expert, but Blind VIAs are usually just VIAs which do not go through - and you do not need to set anything special for them in Altium.

For filled VIAs - I would talk to PCB manufacturer. I do not know exactly if you can fill out all the VIAs or only specific area or only specific VIAs. In any case, if you would like to identify specific VIAs, you can always use specific diameter value which can be used then to filter or identify VIAs. At least, that is how I would do it.

Paul van Avesaath , 10-16-2019, 05:10 AM

quote: " that i see no way to make a complete TH"

I am unsure on what you are asking now.. ?


would a blind via be from top to L3 for instance?

you have to take hole size / vs dept(layer thickness) into account..


plugged and plated via's is something you ask manufacturering like robert said. I normally have a string in a mechanical layer saying someting like " all via's need to be plugged and plated according to IPC.. (some number) "

Anatoliy , 10-16-2019, 05:16 AM

This is what i want to make, in Altium-

from your replies i understand i need to ask my manufacturers for it..
and paul, is this what you were referring to as plated vias?

Paul van Avesaath , 10-16-2019, 05:19 AM

option B is called plugged and plated via.. so yes you have to ask munfacturer to do this.. it will add manufacuring costs to you PCB price so take that into account.
good luck.