Fiducials under chips - Page 1
Forum section: electronics / general

author: pastaclub
author_rank: Regular Contributor
timestamp: February 18, 2025, 07:13:21 pm
content: Is there any good reason, NOT to place a fiducial mark under a large chip (such as a SOIC)?Unless you need them for inspection of populated boards, I don't see why that should not be done.

author: ataradov
author_rank: Super Contributor
timestamp: February 18, 2025, 07:58:43 pm
content: You may want to re-align a partially populated board. It is likely a marginal scenario, but why complicate things if you have board space? If not, then you don't have much of a choice.

author: jduncan
author_rank: Regular Contributor
timestamp: February 18, 2025, 10:12:42 pm
content: But in that case, why are you using SOIC.

author: langwadt
author_rank: Super Contributor
timestamp: February 18, 2025, 10:30:54 pm
content: Quote from: ataradov on February 18, 2025, 07:58:43 pmand if you are doing AOI of the assembled board it probably needs the fiducials too

author: tszaboo
author_rank: Super Contributor
timestamp: February 18, 2025, 11:13:00 pm
content: You don't really need fiducials anymore, pick and place cameras work well enough with generic board features.

author: erikfriesen
author_rank: Newbie
timestamp: February 19, 2025, 03:03:06 am
content: It might work with newer machines, but definitely not ideal. For example, on an older Samsung I run it always checks fiducials every time it starts, so if it is interrupted it wouldn’t work.

author: ataradov
author_rank: Super Contributor
timestamp: February 19, 2025, 03:16:34 am
content: Another option is to place them on the panel side pieces if boards are panelized.

author: Smokey
author_rank: Super Contributor
timestamp: February 19, 2025, 04:04:07 am
content: Final answer = ask your board assembly cm. If they say it's ok (which they probably won't. ), then go for it.

author: Kean
author_rank: Unknown
timestamp: February 19, 2025, 10:56:15 am
content: Quote from: Smokey on February 19, 2025, 04:04:07 amAnd also ask every future CM you might want to use, just in case...Quote from: ataradov on February 19, 2025, 03:16:34 amI almost always do exactly this.

author: Smokey
author_rank: Super Contributor
timestamp: February 19, 2025, 11:37:14 am
content: Quote from: Kean on February 19, 2025, 10:56:15 amdo both

author: SMTech
author_rank: Frequent Contributor
timestamp: February 19, 2025, 11:37:28 am
content: As standard on our Essemtec, the recipe generated from exported pick and place data should contain fiducials that exist on the individual PCB. In the ideal world the co-ordinate data should then be in the pick and place data so that it is precise and relative to the components. This is better than trying to measure its co-ordinates using the gerber data or the fiducial camera for two reasons:1)Gerber tools can grab onto the wrong part of an apparently simple shape and the middle of a component is not a selectable reference so there's a bit of guesswork.2)Measuring it with the fiducial camera can introduce any skew based error the fiducials are trying to remove.So, could you put a fiducial under a SOIC, yes but it could then be concealed if the machine placed the SOIC and then a feed issue caused a production stop. On Essemtec that would then present a dialogue where you could override it but that could affect accuracy, although if your using SOICs maybe that doesn't matter so much.Depending on your board, PCB features can work, some can be a little unreliable (think ringed annulus/vias)and they need to be unique within the fiducial search area. I see plenty of boards where such features are far from ideally located.Fiducials are not only for location, you might use them for Badmark/Badcheck marks on panels, in that instance being under a chip might not matter, on Essemtec at least, even in the event of a production stop, those marks are only scanned before any placement starts and not rescanned if the board is halted & resumed for some reason.

author: jmelson
author_rank: Super Contributor
timestamp: February 22, 2025, 07:58:24 pm
content: All of my boards have hand-assembled through-hole connectors. If I run out of space, I could put a fiducial under one of those.Jon