Are these PCB fiducials?

[salvagedcircuitry]

I was wondering if these "+" marks are fiducials or indications of a positive voltage plane / trace. The PCB fiducials I am used to seeing are a square pulled back soldermask area with an exposed copper circle in the middle. I know they are used for alignment purposes, so I was surprised when I saw these "+" signs implemented in a similar way. As you can see from the photo, the soldermask is pulled back in the background of the "+" sign, the + sign is in copper and not a silkscreen character.
This particular PCB is the input power board on an ARRI cinema camera. There is an 8 pin lemo connector for input power and the camera is rated for 10.5-34v DC.
This is clearly just a simple input board with a few caps and inductors.

Thanks!

[martys]

Not very likely that + signs are anything more than a fiduciary mark, positive ground circuits are rare and the bottom + sign seems to be on a ground plane. Probably locating marks that were used during alignment used during PCB or solder-mask work or alternatively, places to drill mounting holes.

[salvagedcircuitry]

Thanks! I had a feeling they were just fiducials. I traced it out and there are + rails and ground rails on both sides of the board and vias to connect each side.
Thanks.

[rx8pilot]

My P&P can use + as a fiducial, but I have never tried it.

I am sure that ARRI had assigned a small group of engineers to analyze the pros/cons of the chosen fids so that those 3 parts land in the correct spot.

[salvagedcircuitry]

Huh. That would make sense. I thought you only needed one fiducial per side of the board. I guess having 2 or 3 can only aid in accuracy? Do you use multiple fiducials? Thanks.

[salvagedcircuitry]

Having multiple fiducials does aid in automation with pick and place machines. I thought only one was needed. This web page has a nice writeup about it. Thanks for everyone's input
https://www.worthingtonassembly.com/blog/2014/12/29/what-are-fiducials-and-why-are-they-useful

[rx8pilot]

I use a minimum of 3 fids per board but also have panel fids and local fids.

The 'local' fids are usually a single mark close very fine parts like BGA's.

You need enough data to determine position, rotation, skew, stretch, etc.

Short and misplld from my mobile......

[dmills]

'+' was once commonplace as a FID, but modern stuff seems to favour the circle on copper with a pulled back mask and I second the notion of three widely spaced across the board, it also helps catch a board loaded the wrong way around (Seen it!).

Local fids are a good thing is you are going smaller then about 0.5mm pitch, or if the board is very large.

Fid type tends to be a case of asking the board house what they like to see, I have had answers varying from "Don't need them" to "both circles and pluses".

Regards, Dan.