Inner annular ringIAR (Inner layer Annular Ring = 1/2 (Inner layer pad diameter – PHD))


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

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

IAR = (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.


Finished annular ring


FAR (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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