Defect Rate WRT Customer Deliveries

[kylehunter]

My company is a small CM that is going through AS9100 certification. We've been working to nail down some metrics on our defect rate for SMT and THT assembly. I've seen numbers like 100 - 500 PPM defect rates. On a recent job, if I count each component as one potential source of a defect, then we had a defect rate of around 100 PPM.

The issue I've run into, is that all metric information I've found online bases the PPM rate on defects found by an end of line AOI. This seems flawed to me for a few reasons:
1. This assumes that a AOI is 100% accurate, which as we all know, is not true.
2. If a board is not functionally tested, the only real way to know if there is an assembly defect, is when the end customer/client actually uses/tests the board. Which if you base your defects only on your AOI, this rate is not captured.

Ultimately, if we are building boards for a client, with no functional test fixture provided, it is, of course, not possible to deliver 100% of the boards, defect free. So does anyone have any sort of guidance or information that they use to benchmark this? Because if we base it off of my 100 PPM defect rate, if a board has a few hundred components, that means that there will be a couple of percent of boards delivered to the client that will need to be RMA'd back to us to rework.

[thm_w]

You can read some discussion here: https://smtnet.com/Forums/index.cfm?fuseaction=view_thread&Thread_ID=13073

- False fail rate = falsely flagged AOI failures
- Escape rate = failed products that reach the customer

Because if we base it off of my 100 PPM defect rate, if a board has a few hundred components, that means that there will be a couple of percent of boards delivered to the client that will need to be RMA'd back to us to rework.

Escape rate is based on the number of products, not on the complexity of the board (I assume, I don't do SMT work). So yes you'd need the customer to feed that failure information back to you, or return parts to you, to determine what it is. 100ppm would be a 0.01% product failure rate.

Obviously everything that leaves you is going to be expected to be working perfectly.