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Gerber CAM planes

A

Andrew Holme

Jan 1, 1970
0
I'm designing a 4-layer board using PADS PCB. Both inner layers are solid
ground planes. PADS wants me to select "CAM plane" as the inner layer type
and the gerbers are negatives. Is that customary?

The PCB fab wants "right reading when printed" text on every layer. What
does this mean?

I think it probably means:

Top Copper = Normal
Inner Layer 1 = Mirrored
Inner Layer 2 = Normal
Bottom Copper = Mirrored

When viewed from above looking down and through the stack.

TIA
 
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Andrew Holme

Jan 1, 1970
0
John Larkin said:
Lately we haven't been declaring CAM planes in PADS. We just do a huge
copper pour on, say, layer 2, and attach net name "gnd" to that pour.

That avoids having to deal with keepouts - which often don't work -
and allows us to flood over vias. PADS, or at least our version,
always places thermals on CAM planes, even if you don't want them. You
can cheat and route a little on the "ground plane" too!

The split/mixed plane was always a nightmare in PADS.

CAM plane film comes out reversed, namely mostly clear. Our board
houses are fine with that.

What version of PADS are you using? We stuck with v 5.0.

John

Thanks for that John. I'm using PADS2007.

This was a 1.6mm 2-layer board, bottom flooded with GND and no thermals on
GND vias until about an hour ago; but I have some (short) traces carrying 1
GHz that really should be 50-ohm and that forced me to use a 4-layer
stackup, even though the extra 2 layers are just solid ground and the bottom
is 99% ground! My longest 1 GHz path is about one-tenth of a wavelength
from a Mini-Circuits VCO to a Hitite prescaler via a resistive splitter and
AC coupling cap. This was carried by wider traces (but nowhere near
50-ohms) on the 2-layer version.
 
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