Are polarity markers always at pin 1 (lowest pin number) or can there be cases where they mark some other pin?

We currently seem to have some SMD LED packages (PLCC-x) that mark pin 3 instead of pin 1. The reasoning behind this seems to be that the parts intended for these footprints mark pin 3 on their package.

My interpretation of the IPC standards (that i can find on the internet) is that the polarity marker always marks the pins with the lowest “number” (1, A1, …)
Can anybody with more understanding about industry standards comment if my interpretation is correct?

As they say “it’s the exception that tests the rule”. Maybe you are referring to WS2812B? Some Chinese companies seem very relaxed about standards, ie. they just ignore them.

I think the whole point of IPC rules is that “pin 1 mark is always pin 1”. If it is sometimes not pin 1, then it becomes useless.

So what to do with manufacturers that ignore the guidelines? I think the principle is that we should keep our guidelines consistent, rather than trying to encompass non-compliant manufacturers. The WS2812B will probably confuse everyone who uses it, but at least users should not have doubt about other parts in the libraries.

I would say, orientation as in ipc, but markings on fab and silk in a way it’s clear for the user (on pin 3 in this case).

Right, but is that “clear to the user that knows on this part the mark is pin 3”, or “clear to the user that expects the mark to be pin 1”?

E.g. Which is pin 1 in these pictures?

I agree. Mark Pin 1 according to IPC, using, e.g., the dot, notch, corner cut, etc. If the manufacturer uses some other pin as a reference point in his documents, then it is acceptable (not mandatory) for the footprint to label it appropriately. Appropriate labeling depends on the particular device, of course, but might be “Pin 3” or simply “3”, “K”, “GND”, “Out”, etc.


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