Footprint requirements for Centroid File

I have a PCB that is currently with a CM for fabrication/assembly. They came back to me with placement questions on a couple of components. I assume this is due to the footprints I used having some missing data.

Where can I find a tutorial or other data that describes the requirements for footprints to correctly permit Kicad to generate the Centroid file. I assume it is the footprint that carries this data.


What’s a ‘Centroid file’ anyway?

As for foot prints, they are defined by their respective manufacturers footprint, and landing pattern layouts.

Lots of PDFing to be done. It is a good practice to double check on those layout requirements especially for not frequently use components.

What is a “CM”?

What exact placement questions? And, for exactly what Part Numbers?

The file needed by the assembly house that tells the pick and place machine where to place which component. It contains the center point relative to some reference point (In kicad this is either the auxilary axis or the global coordinate system.) plus the rotation of the part (relative to how it is drawn in the footprint editor.)
In KiCad this is generated under PCBnew -> File -> Fabrication output -> Footprint position (.pos) File…

Does it matter? The important part is in the next few words of the quote: “for fabrication/assembly.” And from the full text we can tell that the question is about some problems arising from the kicad generated centroid file. (or pos file)

Could you go into detail what the questions were? Was the question about which part to use, about the orientation of the part or something else.

If it is about orientation then you might want to look into IPC zero orientation definitions. For example see this explanation of zero orientation

Sadly there are two standards (orientation A and orientation B). The official lib uses orientation A.


The questions were about the polarity of a capacitor, i.e. which pad is “+”, and on some LEDs the questions were about which pad was the anode.

Many thanks, I will read the link you referenced.

I really appreciate your response here, the initial responses I found a little less than friendly or supportive. Restores my confidence in the forum as an excellent source of information.

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It’s good to give as much information as possible, within the limits of clarity, in the Silk layer but especially in the Fab layer. KiCad’s own footprints should offer enough information so that polarity is unambiguous by looking at those layers. The assembly crew probably looks at the Silk, but may need a note about the Fab layer (unless you have renamed it so that it can’t be overlooked). If the ambigous footprints were made by you and don’t offer enough information, change them for the future.

Watch also

(from KiCon 2019).

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@sidprice Oftentimes I don’t write a book long reply for simple questions. I asked the two questions that I thought would help answer the questions in your OP. Apologies if my reply in any way seemed unfriendly or unhelpful.

The point was that I did not know for certain if knowing the definition of “CM” mattered. The issue is aggravated by the fact that I do not recall anyone using the term “centroid” for the position file.
BTW, Google “CM” and see what I ended up with.

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