I am making gerbers where I want one edge of the PCB to have castellations ( plated half-holes) on the edge.

What is the safest way to specify castellations in the gerbers that will ensure that:

  1. The fab how makes the castellations "properly", without making any mistakes. For example one possible mistake is that if the castellations are specified as vias chopped in half by the edge, then a CNC router cutting the board edge may tend to rip the copper off of the castellation through its high-speed spinning motion.
  2. The flat edge itself must be plated - not just the hole part!! See how the flat part of the edge is supposed to be plated in the vicinity of the hole:
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    Seems to me that you should be asking your PCB shop, since ultimately they will be the one making them. – user3624 Aug 6 '13 at 4:42
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    Definitely, but I also figure there might be a "standard" way of specifying this. – AlcubierreDrive Aug 6 '13 at 5:32
up vote 3 down vote accepted

Adding to what markrages already said: most board fabs will plate any copper that is over or directly touches the edge of a hole or routed feature. So a 'standard' way of defining this is just to have copper over the edges of your castellations. This is how vias and plated through holes work - and conversely, this is how non-plated holes work as well (you just pull back the copper a little bit from the hole).

This will work fine with very cheap board houses that are hard to communicate with (e.g. iteadstudio, pcbcart, makepcb). Almost always at no extra charge, it's just part of the workflow. However, if you are doing a production run you will definitely want to communicate any and all special features. Make sure that it is abundantly clear what you mean, use pictures and highlight what you want in the pictures as well as in the gerber files. That will save you from having to do multiple test runs (and waste everybody's time) before you go into actual production.

Castellations are special, custom, and highly fab-dependent.

I've done it with holes that are cut in half by the outline layer. But I supplied an extra drawing explaining what I wanted. The castellations came out fine after some negotiation. The board vendors tend to do some massaging of the CAD data anyway, so whatever extra work was required for castellations did not bother them.

The plating is an extra step that has to be done after routing, so expect to spend rather more money than a standard-spec board would cost.

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