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PCB assembly - only fitting SMT parts on mixed technology boards
1997 1 Dec 12.2019, 18:34:16

Hi all,
I've hand-built some SMT prototypes in the past, but am now looking at getting my first batch of small boards assembled by a contract manufacturer (probably a China-based one, fronted in the UK). This particular board has a number of 9mm pots that protrude through a front panel, and will have 95% SMT devices making up the board electronics. Since the pots will really need to be jigged to ensure that the front panel fits nicely to the completed assembly, I was planning to have the contract assembler just fit all the SMT parts, and to then fit the 9mm pots myself to ensure mechanical alignment. So, the main question is whether there is any problem in having a moderate number (say up to 20) no-fit conventional parts (that I could identify as no-fit on the BOM provided to the contract assembly house) - I guess that this should in theory be no problem for them? Also, does it make any difference at all, from an assembly point of view, whether the SMT devices are on the same side of the PCB as the pots, or the opposite side of the board? I was thinking of doing the latter, since it would seem that this would give better access to the SMT parts if any rework is needed. 
Very many thanks for any input. Cheers!

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Dec 19.2019, 17:51:34

Having no-fit parts is not an issue. Usually referred to as DNP (do not populate).
Having through hole/smd on opposite side doesn't matter, your suggestion of having the SMD available to probe/rework sounds good.
If TH pots were done by them they would either solder by hand, or a separate wave soldering step is done. You could provide a jig for alignment at that point.

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