PCBA First Pass Yield and DPMO Calculator
PCBA customers and EMS quality teams compare assembly lines using DPMO, because it normalizes board complexity. This calculator turns raw defect counts into DPMO, DPU and the first pass yield you should expect.
Your numbers
Total defects at the inspection point, counted once each.
Each placed component is one opportunity.
Each lead, pad or termination is one opportunity.
Your results
The Poisson estimate assumes defects are independent. Clustered defects such as a bad stencil or a single part lot make the true first pass yield higher than predicted, because defects pile onto fewer boards.
Expected first pass yield vs defects found
Sweeps Defects found from 0 to 200, holding your other inputs fixed.
Automate PCBA yield reporting
Optional: see how defect data from your ERP or MES could feed yield dashboards.
Optional. The tool and every export work without this. No spam.
How to use it
Count boards and defects from one inspection point, such as post-reflow AOI, so the numbers match. Enter placements and solder terminations from the BOM and CAD data. The tool adds them into opportunities per board, divides total defects by total opportunities and scales to a million. Use the same definition every time or trend lines become meaningless.
The formulas
Opportunities per board equal placements plus terminations, in the spirit of IPC-7912. DPMO equals defects divided by total opportunities times one million. DPU equals defects divided by boards. Under a Poisson model, first pass yield is approximately e raised to the negative DPU.
- DPMO compares different board designs fairly
- DPU drives yield directly
- Count one defect per root cause location
Reading the result
With 500 boards, 40 defects and 1,420 opportunities per board, DPMO is about 56 and DPU is 0.08, so expected first pass yield is about 92%. A low DPMO with a poor yield tells you the board is large: yield depends on total defects per board, not only the rate.
Common mistakes
Mixing opportunity definitions between customers is the biggest trap, since some count only terminations. Another is mixing defects from AOI, ICT and functional test into one number, which hides where the process actually fails. Report each test stage separately and multiply stage yields for rolled throughput.
Frequently Asked Questions
What is a good DPMO for SMT?
Many EMS providers aim for well under 100 DPMO at post-reflow inspection and higher quality programs target single digits. Targets depend on customer contracts, component sizes and product class, so use your own agreement.
Should false calls count as defects?
No. Count confirmed defects only. Track AOI false calls separately because they cost inspection time but do not reduce yield.
Why use Poisson for yield?
It is a simple, widely used model where defects occur independently. It predicts the fraction of boards with zero defects from the average defects per unit.
How is this different from the sigma DPMO tool?
This tool computes DPMO from PCBA placements and terminations. The sigma converter on the site takes DPMO and shows the sigma level.
Netray can pull defect counts from your MES or ERP quality module so DPMO and yield trend automatically instead of by spreadsheet.
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