Cannot delete Layer from Layerstack

This article describes a couple of scenarios in a Pcb document that can prevent layer deletion in the Layer Stack Manager.

Starting in Version: 19.0
Up to Version: 20.0

Solution Details

Problem: Layer cannot be deleted in the Layer Stack Manager, the option is grayed out.

There are two possible solutions discussed here:

1. Stack symmetry lock for a non-symmetrical board.

2. Limitation in Altium Designer pre 20.1 for adjacent core / prepreg..

Solution 1, Stack Symmetry:

In some cases, possibly caused by importing or copying / pasting from other boards, can cause layer creation resulting in a non-symmetrical board stackup.

In the Layer Stack Manager Stack Properties Panel, there is a symmetry option. If this option is enabled and there is a non-symmetrical stack, this will prevent layers from being deleted.

To remedy in this situation, uncheck the symmetry checkbox which will allow deletion of the layers. When the symmetry option is enabled, a check for stack symmetry is performed, but certain board level operations can bypass this and create signal / plane layers.

Solution 2, Stack geometry limitation:

In Altium Designer 19, there was a limitation that did not allow two

cores to be stacked together. This results in an error state and does not allow the layer to be deleted. This is resolved in our Altium Designer 20.1.7 release.

As a workaround to fix the stack in AD19:

1. Review all the layer names and rename any layers to be sure they are unique.

2. Change the Type of one of the adjacent cores from Core to Prepreg.

Once all the errors are resolved, you can delete the layers.

The improvement in Altium Designer 20.1 was #36545 and is listed here:

https://www.altium.com/documentation/altium-designer/release-notes-for-altium-designer