# Altium - Defining top or bottom layers as a plane layer

I have four layer PCB stack up but wish to use the bottom layer as a 'plane' layer instead of a signal layer. Is it possible to configure Altium like this through layer stackup manager?

• L1 Top - Signal
• L2 Mid - Plane
• L3 Mid - Signal
• L4 Bottom - Plane

I can use multiple polygons but for my design a negative plane definition with splits would be easier to work with.

• I don't recal exactly how to do this, but I do know that most people (at least the ones I talk to) advised against the use of plane layers in altium. If my memory serves me right, plane layers do not properly do DRC. – Joren Vaes Jul 1 '18 at 9:41
• @JorenVaes I've been using Altium since it was called Protel, and never had a problem with DRC on plane layers. I wouldn't be surprised if there is some particular situation that causes a problem on some particular version of Altium, but I don't think a blanket rule against using plane layers is justified. – The Photon Jul 1 '18 at 13:58