Engineering Dictionary of Electronic Terms
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Minimum Annular Ring - Pad Shape
The minimum annular ring on a plated thur-hole is the minimum amount of copper between the hole and the edge of the pad after plating of the finished hole regardless of the pad shape.
Irregular shaped pads are covered below.
Elongated Copper Pad
The elongated pad [shown below] is not very common and should not be found under normal circumstances in a Printed Circuit Board [PCB] layout. However the pad shape is provided for completeness.
Minimum Annular Ring; Elongated PCB Pad
Shaved Copper Pad
A shaved would be much more common on a Printed Wiring Board [PWB]. The PWB designer could always need more space to run another trace between adjacent pads. But with the high pitch BGAs available today the pad is already at its smallest diameter. So a shaved pad will only be found on low speed, low integration circuit card [less than state-of-the-art]. However the distance between the trace and lower side of the via is valid regardless of the application.
Minimum Annular Ring; Shaved PWB Pad
Design hint;
Both of these pad shapes apply to a circuit card regardless of the number of board layers. Either two layers [top, bottom] or a ten layer board and the same distances apply.
The minimum Annular Ring will apply regardless of the pad shape.
Circular Pads; Minimum Annular Ring.
Definitions; PCB Terms.
More Printed Wiring Board Information and specifications
Editor note; I don't remember ever coming across an elongated copper pad that appears as the diagram does. Maybe it was more common years ago before the layout tools become more sophisticated or maybe the shape is just being used to represent a pad that is larger than it needs to be. In any case, any time I've had to increase the pad size on a PWB the shape change was more symmetrical, maybe turing into a rectangle. Of course, what ever the shape, the dimension is still valid.
MIL-STD-275E - Printed Wiring for Electronic Equipment
What is Minimum Annular Ring. Define Minimum Annular Ring
