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I am working on a PCB that (among other things) accomodates an MCU which is available either in a SOIC-14 or SOIC-16 package. Both packages are pin-compatible, the SOIC-14 is simply shorter to one side. This allows me to use the same PCB with a SOIC-16 footprint on it but populate it with either chip, depending on which one is available.

So far so good. Problem: the coordinates in the pick-and-place file always refer to the middle of the chip. That means I cannot use the same pick-and-place file - instead I have to offset the coordinates by half a pin.

I wonder if there is any best-practice to handle such a situation. Of course I can manually edit the pick-and-place file easily, but it would be quite nice to somehow handle it within the CAD tool and generate the correct file automatically. I cannot think of a smart way to achieve that... I guess the right way would be to have both chips in the BOM but assign a part only to one of them. But if I were to put two overlaying footprints on the PCB, I'd get errors because the courtyards overlap (although the pads are connected to the same nets).

(my CAD tool is Altium CircuitStudio)

How can I accommodate chips with a different pin count?

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  • \$\begingroup\$ maybe easiest to edit the position file by hand. However, placing a 14-pin on a 16-pin pad, it might be a minor pain to communicate to the PCB assembly vendor that it's not a mistake. The one's I've interacted with (limited experience however), a component not matching the footprint in even more minor ways have generated an email or phone call, could possibly hold up the process \$\endgroup\$ – Pete W Mar 18 at 19:35
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The way to do this is commonly done with variants, but you have to produce two design files, you can use the same schematics and output two different designs (boms or PCB's). This also helps with manufacturing because you only send one set of files to the manufacturer and this creates less confusion.

For example:

I have boards with parts that use the same PCB, but have different parts loaded for the same component, I use variants to keep track of the parts and create two different BOMS's. I then keep all the files in the same zip folder and create two zip folders for each variant. When I want to order I send the correct zip file to the assembler and they build that design.

The different pin count might be tricky with a variant but doable.

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