Determining PCBA Xray Test Sampling Size

[alonFAI]

Hi guys

I work in a PCBA manufacturing line.
we manufacture a card that we have to perform XRAY test for 100% of the manufactured cards. (customer request). we have very high FPY and we want to ask the customer not to check in XRAY 100% of the cards but based on a sample.
what sample should I take? according to what, ansi z1.4? mil-105? (what is the difference between those 2 standards). the problem is if we make in a quarter for example 200 card, we don't manufacture them all together, but for example we make 50 after a month another 50 and so on..
so if I do the sample out of 50 every time I would sample much more then I need opposing if i do the sample out of 200.
did i make any sense?
can someone please help

again thank you all!!

 

[Bev D]

Z1.4 simply replaced mil-std 105. there really is no substantial difference between the two standards.

your sample size really should be based on the batch size. you can base it on the shipping lot size IF you properly randomize across the lot, but if there were a problem with one batch and not another you have a non homogenous distribution of defects and even a random sample may under protect your customer. especially if your plan is based only on an AQL and not a combination of AQL and RQL...

but the biggest concern you should address with your customer and yourself is that you have effective controls on the process(es) and materials such that defects are highly unlikely. the simple absence of defects in the past is no guarantee of defect free parts in the future. I have experienced this all too often.