Solder Joint Defect Log with DPMO
A defect log is only useful if you can turn it into a rate. This worksheet captures each solder defect with its cause and computes DPMO, defects per million opportunities, so you can compare lots, lines and shifts on one scale.
| Date | Board / lot | Ref des | Defect type | Suspected cause | Boards inspected | Opportunities per board | Defects found | Total opportunities | DPMO | |
|---|---|---|---|---|---|---|---|---|---|---|
74,000 | 81 | |||||||||
74,000 | 41 | |||||||||
66,600 | 60 | |||||||||
66,600 | 30 | |||||||||
96,200 | 52 | |||||||||
96,200 | 10 |
Opportunities per board is usually the count of solder joints plus placements, as agreed with your customer or your own method. Keep the counting method constant so DPMO trends are comparable. Enter one row per inspection batch and defect type.
Feed defect data from your MES automatically
An optional review of how inspection results can flow into DPMO and Pareto reports.
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How to use the log
Add a row for each batch and defect type found. Enter boards inspected, opportunities per board and defects counted, and the sheet calculates total opportunities and DPMO for that row. The summary shows overall DPMO across the log. Export to Excel and sort by defect type to build a Pareto for your next quality review.
The DPMO formula
DPMO equals defects divided by total opportunities, multiplied by one million. Total opportunities is boards inspected times opportunities per board. In the sample data, forty boards with 1,850 opportunities each give 74,000 opportunities; six defects therefore equal about 81 DPMO. Overall DPMO uses summed defects over summed opportunities, not an average of row values.
- Do not average row DPMO values, compute from sums
- Define opportunities the same way every time
- Count each defect once, per its location
Using the data
Group defects by cause to see where to act. A cluster of bridges and solder balls tied to paste print points to stencil, squeegee or printer settings. Tombstones suggest pad design, placement offset or reflow ramp. Voids call for profile, paste and board finish checks. Record the corrective action against the lot so you can see whether the rate moves.
Common mistakes
Teams change how they count opportunities between months and then wonder why DPMO moved. Others log only rejects and skip process indicators, losing early trend data. Another is mixing defects found by AOI with defects confirmed by a human, which inflates the count with false calls.
Frequently Asked Questions
What is a good DPMO for PCB assembly?
It depends on how opportunities are counted and the complexity of the product. Many shops track their own trend and aim for steady reduction. Compare only against figures that use the same counting method.
How do I count opportunities per board?
A common method counts every solder joint, plus a placement for each component. Some customers specify their own method. Pick one, document it and keep it fixed so results are comparable over time.
Should AOI false calls be counted?
No. Count confirmed defects only, and track false call rate separately. Mixing them overstates defects and hides the true process capability.
Can I log defects found in test or at the customer?
Yes, but keep a column or separate log for detection point. Defects found later cost more, and the escape rate between inspection and test is itself a useful measure.
Netray can pull inspection results from your MES or ERP quality module into this view automatically so DPMO updates itself each shift.
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