PCB labelling bare part number vs assembled part number

Question

1st time posting question here.

I'd like feedback on best practice for labelling PCBs with the board (bare PCB) Part Number (PN) and/or assembled (PCBA) part number. We give bare PCBs a PN, then the assembled PCBA gets different PN, however within the company there's a lot of division over what should be printed on the silkscreen. Bare PCB number only, PCB + PCBA numbers or PCBA only. PCBA makes it easier for production staff to identify but makes design changes difficult since even a component replacement requires silkscreen update, not to mention I want to introduce variants, so we have same PCB used in multiple PCBAs. This is complicated by us being medical device designers/manufacturers so there is lot of concern around traceability. In summary what's best practice;

1. only bare PCB part number on silkscreen (or copper)
2. bare PCB part number & assembled PCB part number printed on board
3. only assembled PCBA part number printed on board
4. bare PCB part num printed on board, label PCB assembly part number with adhesive label
5. other?

Note we do include versions but I've left out of discussion to keep it simple

Andrew

Answer 1

Number 4 is a common practice and avoids the ambiguity inherent in the other options. Contract manufacturers tend to be familiar with it as well. You can / should put the PCB PN on the PCBA BOM. You didn't mention serialization, but it also plays well with that since you can keep the PCBs traced by lot (typically printed somewhere on the PCB, perhaps near the PCB PN) while tracing the PCBAs individually - just have the adhesive sticker contain a unique PCBA SN as well as the PCBA PN. It's convenient to include a QR or bar code.

Answer 2

This is a very opinion-based question.

In our situation, we use a product number with a revision number, for instance, the product can ABC-XYZ23-3 v4.2 revB which is P/N, Version, Revision

The ABC-XYZ23-3 is the assembled product, and 4.2 is the version number.

Any change in the PCB or the BOM would increase the revision number.

Any major change would change the product number.

Any minor change that wasn't sent for manufacturing would change the revision. Increase in version reset the revision number.

Overall, it's very important on the silkscreen to have an identifier that is specific to the very version of the PCB, otherwise, it may be a big headache for the engineers to debug stuff.

If you only put SMT identifier, you may have PCB modification that doesn't impact the BOM, or BOM modification that doesn't impact the PCB.

Just think of the people in the loop between your company and the PCB manufacturer, you may have different file version, someone may mess up and the wrong file may end up being manufactured, if you don't have any silkscreen indication, it will be difficult / too late to realize it.

It is also useful if you have different versions over time. An engineer debugging a system may want to know exactly which PCB he has to deal with, issues over time are usually tracked from their symptoms, you will know "haaa PCB xxx v2.3 revB has this problem that was fixed in v2.6".

If you can identify which actual PCB file is the PCB from the silkscreen you will avoid a lot of headaches and simplify the life of the engineers.

Usually, PCB and BOM go together, so it makes a lot of sense to have them both if your QMS needs it, it's not like you are paying extra. You can even put barcodes so you can scan them.

Labels are usually not a very good idea, wrong labels can be applied, people can change them, they can degrade and become unreadable over time and it's extra work to order the supplies, print them and put them on. Only makes sense for serial numbers.