Name the two features being aligned
A positional tolerance is incomplete without a reference. Distinguish laser opening to target land, layer to layer, hole to outer pad, and solder mask to copper. These relationships may use different measurement methods and cannot be replaced by one generic registration number.
Ask whether the stated value is a radial displacement, a diametral zone, or another convention. Applying a tolerance twice, or only half as much as intended, can make a calculated margin misleading.
Use a transparent margin calculation
For a deliberately simplified illustration, a circular land of 200 micrometers around a 100 micrometer opening has a nominal radial difference of 50 micrometers. If relative center displacement is 25 micrometers, the narrow side falls to 25 micrometers before size variation and other allowances. These are teaching dimensions, not manufacturing recommendations.
The calculation demonstrates why pad-minus-hole is not the final acceptance margin. Use the supplier's definitions and the applicable product requirements to construct the real tolerance budget.
Avoid a single global allowance
Different layer pairs and process stages can have different constraints. Dense features near one package may be the limiting region, while a large land elsewhere has ample margin. Altium's annular-ring documentation connects land selection to manufacturing variation; the practical response is to scope rules to the actual structure.
- Identify capture and target lands independently where needed.
- Include the permitted range of hole and land dimensions.
- Review the narrowest remaining connection to a trace.
- Check neighboring clearance as well as landing coverage.
Choose the corrective action deliberately
If margin is inadequate, options include increasing the land, changing the opening or dielectric depth, adjusting the route, or selecting a different interconnect sequence. A larger land can consume a routing channel, so repeat the escape study. The best correction preserves both manufacturing margin and the electrical layout.
Adjacent-layer access, one connection at a time
Dielectric · geometry + material
Core or build-up dielectric
Illustrative only. Copper thickness, dielectric construction and via spans require a reviewed stackup.
Common questions
Is nominal annular ring the guaranteed finished ring?
No. Position and dimensional variation reduce the remaining margin. Finished acceptance must be defined and evaluated separately.
Can teardrops replace a registration review?
No. They may help a particular trace-to-land connection, but do not establish acceptable landing geometry or clearance for the complete structure.
References & further reading
Method & assumptions · General design guidance. Validate the proposed construction and acceptance criteria for your project.