"A"
"B"
"C",
"D",
"E",
"F",
"G",
"H",
"I",
"J",
"K",
"L",
"M",
"N",
"O",
"P",
"Q",
"R",
"S",
"T",
"U",
"V",
"W",
"X",
"Y",
"Z"
Minimum Annular Ring
The minimum annular ring on a plated thur-hole is the minimum amount of copper (at the narrowest point) between the hole and the edge of the pad after plating of the finished hole. MIL-STD-275E and IPC class 3 calls for a minimum annular ring of 0.05mm (0.002") edge of hole to edge of pad. MIL-STD-275E also calls out .005 inches for via to trace distance.
Minimum Annular Ring; PWB Internal Via
Both diagrams indicate minimum annular ring measured from the outside ring of the pad and to the inside diameter of the plated thru-hole for an external pad [below], or to the center of the plated via for an internal pad [above].
Minimum Annular Ring; PWB External Pad
Minimum Annular Ring applies regardless of the shape of the PCB pad. The next page shows two examples of different pad shapes.
More Printed Wiring Board Information and specifications
MIL-STD-275E - Printed Wiring for Electronic Equipment
