OAR (Outer layer Annular Ring) = 1/2 (Outer layer pad diameter – PHD)
Outer annular ring


Calculation of annular ring : OAR = (Copper pad diameter – TOOLSIZE)/2
TOOLSIZE = ENDSIZE + 0.10mm for all PTH holes
+ 0.00mm for all NPTH holes

Calculation for OAR on a copper pad of 0.60mm and finished hole size diameter of 0.25mm(PTH):

OAR = (0.60mm – (0.25mm + 0.10mm))/2
= (0.60mm – 0.35mm)/2
= 0.250mm/2
= 0.125mm

This corresponds with our pattern class 6 which is standard for our pooling services. See Eurocircuits Classification.

What do we allow in case of mis registration?



Around PTH and NPTH : 90° breakout allowed (A). 90° breakout acceptable at land to trace junction (trace not reduced by more than 20 %) (B)


Finished annular ringFAR (Finished Annular Ring).

The area lying between the outer rim of the solder pad and the solder hole. As a result of the hole being drilled more or less off-centre, the annular ring may be broken.This depends on the nominal outer diameter of the solder pad against the nominal diameter of the hole.

  • The width (t1) of the annular ring on outer layers must be >= 0,050 mm on the finished board.
  • The width (t2) of the annular ring on inner layers must be >= 0,0100 mm on the finished board

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