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I'm developing a new PCB and I realized that all my power connections are on one side of the board, easily connected with a wide trace. So, I don't really need the inner power layer of the board. I do need an inner ground, though, since the ground connections are just all over the place. I don't have the option to order a 3-layer board from my manufacturer, so I'm stuck with a 4-layer board with internal power and ground.

Since I'm not using the power layer, should it be grounded? I'm thinking of grounding it at a single point there the power enters the board.

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As to why your fab doesn't offer 3-layer boards, see electronics.stackexchange.com/q/108717/2028. – JYelton May 22 '14 at 22:32
up vote 8 down vote accepted

If you don't need the second inner layer, then grounding it to match the potential of the other inner layer is a perfectly acceptable idea.

Instead of grounding it at a single point, you should strongly consider "stitching" it using vias in as many places as make sense, to maintain the layers at the same potential.

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Thanks for the reply, I'll do that! – Ben S. May 22 '14 at 22:37
If you define both inner layers as Ground, then any grounded vias or through-hole component pins will connect to both planes, and help to stitch the two planes together. (You could tell the board shop to use the same Gerber file for both internal planes - but that might confuse them...) – Peter Bennett May 22 '14 at 22:44

If you are going to get a 4 layer board, I'd suggest using the "extra" internal layer for power. The solid copper plane will reduce voltage drops across the board, and the capacitance between planes will improve power supply bypassing. You don't need to do much for this - just define the plane as Vcc, and it should automagically connect to all the Vcc vias and component pins. You don't need to remove the now-redundant Vcc traces on the surface layer, unless you want to.

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