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Full changelogEngine 1.18.3

Via & Pad Geometry

PCB & Copper

Annular ring after drill registration, aspect ratio and clearance against your fab's limits, with the smallest pad that passes.

Inputs

Board profile

Fills Board thickness and Finished hole size from your board profile.

Fab profile

Fills Fab minimum hole, Fab minimum annular ring, Drill registration tolerance, Fab maximum aspect ratio and Fab minimum copper clearance from your active fab profile.

The plated size you specify. The fab drills larger.
Pad edge to the nearest trace, pad or pour
From the capability sheet
How far the hole may land off centre, from the capability sheet
Board thickness ÷ hole. 8:1 is common; higher is a premium process.

Results

1 passed · 1 to check
Annular ring

(Dp − Dh) / 2 · 100 µm after registration
150µm
Check

Checked: ring after 50 µm of drill registration ≥ 125 µm, the fab minimum
Ring after registration

with the hole 50 µm off centre
100µm
Aspect ratio

limit 10:1
5.3:1
All results (2)
Smallest pad for this hole

Dh + 2 (ringmin + treg)
650µm
Copper clearance

minimum 150 µm
200µm
Annular ring 150 µm meets the 125 µm minimum only with the drill centred. With 50 µm of registration error it is 100 µm. Grow the pad to 650 µm.
Aspect ratio 5.3:1, inside the fab's 10:1.

These limits are the fab's, not a standard's. IPC-6012 sets ring acceptance by product class; the capability sheet says what this fab can hold. Re-check when you change fab.

worst-case ring for this hole

Accuracy

Verified against

3 independent cases. See the working.

This is a design aid. The engineer remains responsible for the design and for checking the standard itself.

Parameter sweep

Vary one input over a range and see the answer and verdict at each step, as a table and a curve.Pro

Worst-case corners

Put a tolerance on each input and get the worst-case band around the answer.Pro

Give at least one input a tolerance above zero.

Geometry

The principle

The drill never lands exactly where the artwork says. The annular ring is the copper left between the hole wall and the pad edge, and the fab sets how much must survive after the drill wanders. Aspect ratio is the other limit: a deep, narrow hole is hard to plate in the middle.

Annular ring
ring=Dp−Dh2\t{ring} = \frac{D_p - D_h}{2}
Ring after registration
ringeff=Dp−Dh2−treg\t{ring}_{eff} = \frac{D_p - D_h}{2} - t_{reg}
The hole may land up to treg off centre, so the ring on one side shrinks by that much.
Aspect ratio
AR=TDhAR = \frac{T}{D_h}
Smallest pad
Dp,min=Dh+2 (ringmin+treg)D_{p,min} = D_h + 2\,(\t{ring}_{min} + t_{reg})
IPC-2221 writes this as hole + 2 × ring + a fabrication allowance; here the allowance is the registration.
  • DhD_hfinished hole size
  • DpD_ppad (land) diameter
  • TTboard thickness
  • tregt_regdrill registration tolerance from the capability sheet
  • ringminring_minthe fab's minimum annular ring
More detail

Specify the finished (plated) hole. The fab picks a larger drill to allow for plating, and quotes its limits in finished sizes.

When the drill wanders off the pad the hole breaks out. IPC-6012 sets how much breakout each product class accepts; the fab's capability sheet says what it can hold.

Check the ring after registration, not before. A pad that meets the minimum only with the drill centred will fail on some holes.

A deep, narrow hole plates thin in the middle and can crack under thermal cycling. Laser microvias follow a different rule: depth about one hole diameter.

0.3 mm hole, 0.6 mm pad, 1.6 mm board
Ring = (0.6 − 0.3)/2 = 0.15 mm. After 0.05 mm of registration it is 0.10 mm, under a 0.125 mm minimum: the pad meets the fab only when the drill is centred. Aspect ratio 1.6/0.3 = 5.3:1, fine. The smallest pad that passes is 0.3 + 2 × (0.125 + 0.05) = 0.65 mm.
References: IPC-2221B, Generic Standard on Printed Board Design, on land size and fabrication allowance. IPC-6012, Qualification and Performance Specification for Rigid Printed Boards, for the annular ring and breakout acceptance by class. IPC-2222 for rigid-board design detail. Your fabricator's capability sheet for every number used here. Related: Via Current & Resistance, Conductor Clearance & Creepage.

Engine version ⁨1.18.3⁩