IAR (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
This corresponds with our pattern class 6 which is standard for our pooling services.
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 >= 0,100 mm on the finished board