One pet peeve of mine- I've had it happen twice on high-current designs- a board house adding thermal reliefs to all the through-hole components. A near disaster. Needless to say, we don't use those houses any more. Funny thing is, they acted very baffled as to why we would be angry about that.
As for plating edges, I have had this done several times. I don't believe it's all that uncommon. In a case with RF components near an edge, and the board mounting surface being a chunk of aluminum that follows the perimeter underneath the board, the RF can flow right off the edge of the board and down to the aluminum case "ground plane" with very little inductance. This is especially effective with thicker boards, where proper GND via diameters can get pretty large. I have seen a few cases where edge plating seemed to really make a difference. A well placed set of stitching holes appears to be almost equally effective though in the majority of situations, and I generally get by with that.
Funny you should mention this right now, I was kicking around the idea of plating an edge of our new receiver board and see if it accidentally had any effect.
At 03:21 PM 11/9/2001 -0500, Abdulrahman Lomax wrote:
At 09:44 AM 11/9/01 -0700, Bob Fearon wrote:
Yes I have seen an inner plane layer come all the way out to an edge.
The design was supposed to be "better for RF", but made no difference
in board performance. The two outside layers were plated aound the edge
and shorted ( on purpose ) to the inner layer. This was a nightmare to
build and cost "extra".
The same performance was achieved by placing a row of vias 100 mils
from the edge on a "regular" board, at a much lower cost.
This is not an example of what I asked for. Instead, this was a board deliberately fabricated without edge clearance. Yes, it was not a great idea from the start, as anyone who knows HF design would have anticipated, unless -- maybe -- one was trying to squeeze the last percent out of noise emissions *and* board space was very limited. I could see doing this with very small PCBs, where the via ring would take up an appreciable percentage of the board space.
It should not have been much more expensive. In fact, as I recall, depending on the process, panel edges plate if you don't do something to prevent it! (The same electroless copper used to plate the inside of holes also plates the panel edge, I'd think, I don't remember actually seeing this; however, that edge is normally routed away when all the processing is done, leaving the unplated edges that we normally see. So to accomplish this relatively inexpensively, one would route the boards as one routes a breakaway board *before* going to the electroless copper; this would leave some unplated tabs but one might hide the unplated tabs behind mounting holes....)
Edge effect with regard to radiated noise is a controversial subject, but actually plating the board edge I have never before seen suggested.
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