The annular ring is the width of copper between the edge of a drilled hole and the outer edge of its pad. Drills wander and layers shift in lamination, so designers size pads to leave enough ring after worst-case misregistration. IPC Class 2 accepts breakout of up to 90 degrees of the ring on external pads provided the conductor junction is not reduced too far, while Class 3 requires a minimum external ring of 50 micrometres all the way round.
Drill registration is off at the panel edge, the annular ring breaks out on half the vias, that lot fails Class 3.
Also heard as
- AR
- ring
- pad ring
Related terms
Breakout
Drilled hole wandering past the edge of its pad, or the routing that escapes signals from a dense part.
Via
Plated hole that connects copper on one layer of a board to copper on another.
PTH
Plated through-hole: a drilled hole whose walls are copper-plated to connect every layer it passes through.
IPC class
Reliability class 1, 2 or 3 under IPC standards, setting the acceptance criteria a board is built to.