Solder Defect DPMO and First Pass Yield Calculator
DPMO lets you compare an assembly line building small boards with one building dense boards, and it is the standard way to report solder and placement quality to customers. This calculator also converts defects into first pass yield and sigma level.
Your numbers
Count every defect, not only defective boards.
Solder joints plus component placements plus other defined defect opportunities, counted the same way every time.
Labor, rework and re-inspection.
Your results
Poisson yield assumes defects are independent and random. Clustering of defects on a few boards makes real yield higher than this estimate. Define and freeze your opportunity count method, for example by IPC-9261 or your customer rules.
First pass yield vs defects found
Sweeps Total defects found from 0 to 200, holding your other inputs fixed.
Defect trends joined to ERP work orders
Optional: discuss how AOI and test defects could be linked to part numbers and lots in your ERP.
Optional. The tool and every export work without this. No spam.
How to use it
Enter how many boards you inspected, the total number of defects found at inspection, and the number of defect opportunities per board. Opportunities are usually the sum of component terminations, placements and other defect checks defined in your method. The tool then calculates DPU, DPMO, expected first pass yield and sigma level, plus the rework cost of the sample and the DPMO gap to target.
- Use the same opportunity counting method every month.
- Count defects at one defined inspection point, such as post-reflow AOI.
- Separate true defects from false calls before entering data.
The formulas
DPU is defects divided by boards. DPMO is defects divided by the product of boards and opportunities, times one million. Under a Poisson model the chance a board has no defect is e to the minus DPU, which approximates first pass yield. Sigma level here uses the inverse normal of the yield per opportunity plus the conventional 1.5 shift. IPC-9261 describes defect counting for assembly; check it and your customer rules for the official method.
Reading the result
With 36 defects on 500 boards of 2,400 opportunities, DPU is 0.072, DPMO is 30, expected first pass yield is about 93 percent and the sigma level is about 5.4. A good DPMO can still give poor yield on a very dense board, because yield depends on defects per board, not per million. Use DPMO to compare processes and first pass yield to plan rework and test capacity.
Common mistakes
The biggest error is changing the opportunity definition when numbers look bad. Another is mixing inspection stages: AOI before and after rework, or in-circuit test defects, have different meanings. Do not average DPMO across products with different opportunity counts; recompute from total defects and total opportunities. Finally, small samples give wide uncertainty, so trend with enough boards before concluding a change worked.
Frequently Asked Questions
What is DPMO?
DPMO is defects per million opportunities: the number of defects found divided by total defect opportunities across all inspected units, scaled to one million. It normalizes quality across products with different complexity.
How do I count opportunities?
Define them once in your method, usually each solder termination plus each component placement and any other inspected feature. Industry practice is described in IPC-9261, and customers may specify their own rule.
Why is first pass yield different from DPMO?
DPMO is per opportunity. First pass yield is per board and depends on how many opportunities each board has. A dense board can have excellent DPMO and still show a lower board-level yield.
What does the 1.5 sigma shift mean?
It is a long-standing convention in Six Sigma that allows for drift in the process mean over time. Some teams report sigma without the shift, so state your convention when you quote a sigma level.
If defect data sits in AOI systems, MES and spreadsheets, Netray can discuss a private view that joins it to work orders and part numbers.
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