Swiss Cheese PCB

sunblock · 2012-12-30 22:29

I am trying to understand the "shotgun" effect on this PCB in certain areas. Specifically, how are the hole locations determinef and why do they go all the way thru? I thought a bunch of thru hole vias cause all sort of rf loop and other issues. Someone explain?

WBA Consulting · 2012-12-30 23:59

Those are "castellations" or "castellated holes". They are used to solder the PCB onto another PCB by means of an "edge solder connection". Each of the castellations are for a connection to something on that module. Many bluetooth modules utilize the same type of connections. Do a Google Image search for "pcb castellations" and you will see tons.

EDIT: I was looking at the picture again and I think I mis-understood your question. If you are referring to the vias in the ground planes, it is typically done to reduce RF or ground loops by creating a more consistent ground plane. I assume there is a PCB antenna at the left edge of the board?

MacTuxLin · 2012-12-31 00:16

Also, sometimes you'll see such as exposed thermal pads commonly used in power-related IC for mechanical reliability and to achieve appropriate power dissipation.

WBA Consulting · 2012-12-31 00:21

I had another thought and found the document I recalled. Here is a link to a High Speed PCB layout presentation. Page 91 shows some more notes about the multiple via method of stabilizing grounds for RF and high speed circuitry.

http://www.support.wdv.com/Electronics/Fab/PCB%20Layout/HighSpeedPCBLayout.pdf

Mark_T · 2012-12-31 04:44

Here the board is an RF transceiver board by the look of it - the highest density of ground vias is near the antenna pad (lower left, circle with gold plated pad). Where
the antenna joins the board is the point with the highest RF currents will flow, so lots of copper will reduce resistance losses and allow the antenna to have a higher Q.

tonyp12 · 2012-12-31 08:25

It's a RF board and you should connect the Gnd planes (both sides) as much as possible along edges.
The vias are large (but not that huge as it's a close up), maybe is due to the minimum hole size that pcb manufacture could handle.

sunblock · 2012-12-31 08:53

Yes, there is a PCB antenna at pin 2 of the picture, which as luck woud hvae it I cut off with the picture (figures). The part that makes my head itch is that I read all the time about needing to have a solid ground plane. But doesn't poking a bunch of holes all over the top of the PCB through to the ground plane defeat this process? I must be over-simplfying this somehow. To a software guy, either you have one big solid ground plane or you have a sifter to drain water from pasta. The holes on the board go all the way through. Do they have thermal connections to ground (typically)? or are they just non-connected holes to cut down on wind resistance. Sorry for the sarcasm but some of this hardware stuff makes little sense. The board I'm working is a 4-layer board and is already in the shop for a prototype run. I am asking for after-the-fact if I should have "drilled" a bunch of holes in the thing, and if so, what kind?

tonyp12 · 2012-12-31 09:18

They are not holes, they are vias that connects both sides.
Of course holes need to be drilled and then filled with conductive ink and plated.
Really tiny holes ending most of the time being filled while being plated.

Electricity don't need solid planes to function good, just a like a Faraday cages have a lot of holes its still protects the person inside.

sunblock · 2012-12-31 11:17

My board is a 4 layer.... Can you explain the implementation theory on a 4 layer board? Connecting both sides would be connecting the signal layers and not even touch the inner power or ground layer.

sunblock · 2012-12-31 11:23

VERY nice document! Thank you very much.

Swiss Cheese PCB

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