Layer Pairs - When to use?

[Stupid Bear]

I am confused when is it necessary to use layer pairs.
For example.... in a courtyard/keepout layer is it needed? Probably not for smd but what about thruhole or components that come out the other side? Do you typically create paired drawings or does Altium figure that out itself?

[ajb]

It's needed anywhere you want objects to change layers when you change which side of the board a component is mounted on.  For example, if you set your courtyard to a layer pair and then swap a component from the top of the board to the bottom the component's courtyard objects will automatically switch from the Top Courtyard layer to the Bottom Courtyard layer, just like the pads automatically swap from the top layer to the bottom layer.  Otherwise the parts will just be stuck on the one courtyard layer.  So yes, you DO actually want for on SMD parts! 

Actually this applies to free primitives as well.  Just like when you have an object on the top silkscreen and hit 'L' to flip it to the bottom, you can do the same thing with any object on a paired layer. 

[thm_w]

https://www.altium.com/documentation/altium-designer/working-with-mechanical-layers
https://www.altium.com/documentation/altium-designer/pcb-dlg-altium-pcb-common-documentviews-boardconfiguration-views-addlayerpairdialogadd-component-layer-pair-ad?version=18.1

Previous courtyard thread may be relevant: https://www.eevblog.com/forum/manufacture/overlapping-sot-23-3-courtyards/

[Stupid Bear]

So in the sections Mechanical and Other Layers what kind of things typically go there. I see some people have dozens of layers. Also, for example the drill layer - I thought Altium generated that when it creates an output file or do you go there yourself and put those in?

[ajb]

You can put all kinds of things on the additional layers. You might have layer pairs for top and bottom designator and value, or some other component parameter, or component assembly information, 2D/3D body information, . You might have mechanical keepout areas, paired or not, fabrication notes, scratch layers for reference geometry, layers specific to single/panelized forms of the board, documentation....

For "drill layer" - depends what you mean? The "multi-layer" 'layer' is kind of a special layer for holes and vias, which gets special handling, and yes you get an NC drill file automatically from the information it contains via fabrication output. The other drill layers have other documentation purposes.