What Layer To Place Centroid Marker On?

I have been using PCB Libraries Footprint Designer Pro version 2019.1 to develop my own land patterns/footprints. The program puts the centroid marker, a circle with a cross, on the courtyard layer. I was told that they do this to conserve layers. The program has the ability to turn these off, which I do, because only the courtyard outline is acceptable on this layer. For KiCad what layer should the centroid marker go on? Is there any stipulation in KLC (KiCad Libraray Convention) that addresses this? Thanks.
–Larry

Is your “Centroid Marker” the same as a Fiducial?

Fiducials are used to aling components on pads, and they should always be on the same copper layer as the pads. During manufacturing different layers can have slight offsets. but if the Fiducials are in the copper layer, then they can not shift relative to other copper on the same layer.

(This is not entirely ture because layers can get stretched and warped during production, but it is the closest you can get).

If you "Centroid Markers " are not Fiducials, what are they used for?

@Rene_Poschl will be probably give the best answer but in the meantime this KLC entry might help https://kicad.org/libraries/klc/F6.2/

KLC F6.2 has “Footprint anchor should be placed in the middle of the component body”. And “For most standard components, the anchor should generally be located on the centroid of the component body.” The footprint anchor or centroid is where a pick-and-place machine would pick up an SMT component whereas a fiducial is a spot on a PCB that is used to locate where a component is to be placed.

Note that this clause of the KLC doesn’t state on what layer the centroid mark should be placed. I would think the centroid mark for a component would need to go on the layer having to do with assembly, possibly the *.Fab layer. Is this correct?
–Larry

I have never heard of placing a mark on the center. What the rule refers is that the footprint should be centered around that position. (Either by having 0,0 there or by consciously placing the footprint anchor.)

The reason for this rule is that this point is the reference point for the pos file used by pick and place machines. It should coincide with where the machine “attaches” to the component. For most parts this simply is the center of the body. (I do not know what an optical mark should help with. Pick and place machines use the pos file data directly, the user does not really need to know this position in a way to merrit adding a mark. IPC to my knowledge does not suggest having a visible mark on any layer.)

The page Efcis points to talks about “placing an anchor” and in the Footprint Editor there is an “Anckor” button with tooltip text “Place footprint reference anchor” and this may suggest that some Mark / "anchor is placed on some layer, but it does not do that.
It just shift the coordinates of all graphics on all layer around to that the point you select as the “anchor point” effectively becomes the (0, 0) origin point of the footprint.

The way the text is written I can understand to mis-interpret the “anchor” as being something physical that you put on the footprint of a component.

The first post from 9V1MI seems to suggest there is a “Centroid Marker” in “PCB Libraries Footprint Designer Pro”. I assume that program uses it’s own coordinate system wile designing footprints, and the “Centroid Marker” in that program becomes the (0, 0) coordinate during exports of the footprint, but I’m guessing here.

I can find the “pcb libraries” company":
https://www.pcblibraries.com/Products/FPX/KiCad.asp

But the names they use are such generic words that with an image search you find screenshots of almost every PCB program in existence:
https://duckduckgo.com/?q=PCB+Libraries+Footprint+Designer+Pro&iax=images&ia=images
Combine that with the low resolution of the screenshots so you can’t even read the program name of most screenshots and I quickly abandoned this approach.

“PCB Libraries” has it’s own forum, that may be a better place to ask questions about their software:
https://www.pcblibraries.com/forum/forums.html

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