We are a PCB and PCBA maker. Sometimes, the client just ask us for 1 or 3pcs PCBA. But is not very practical, because the we can not assure all the 1 or 3pcs of PCBA is perfect after assembly, what if something bad happened, also we need to adjust the smt machine before production. So, in my opinion, at least 5PCS PCBA need to be ordered, just to convenient the supplier for assembly and yourself for testing. FYR 