Use of Layer 25

[reneta]

What is the purpose of using "Layer 25" in PowerPCB?.

[Colorado-PC-Dude]

Layer_25 is used by PowerPCB for negative plane (CAM planes) keepouts. If you use positive planes (split/mixed or copper pour) then Layer_25 doesn't do anything for you.

Ben

[reneta]

While designing the board, is it compulsory to use the Layer-25?. What is the main use of Layer-25?. Please give an example.

[Colorado-PC-Dude]

No, use of Layer_25 is not compulsory (unless you want to use CAM planes). It is used by the software the define keepouts for negative image (CAM) planes. CAM planes help keep file size down by only keeping plane keepout information. That is, the keepouts are shown as a visible entity. A copper pour plane or a split/mixed plane has a larger file size because the planes information is kept. It is a visible entity with visible keepouts.

We use only copper pour planes and/or split/mixed planes. We use Layer_25 for dimensions.

Ben

[jjustice]

Layer_25 is used exclusivly for generating negative CAM planes. To be honest, negative CAM planes are a thing of the past. We used to generate them negative to save disk space as a positive plane would cause huge gerber files.

If one of your components is missing the layer_25 keepout, you can short planes together, as PPCB will not DRC check for this. My advise would be to design all your planes positive using the 'split/mixed' layer type under layer definition.

Hope this helps.

When in doubt, tools down and go mountain biking...

[Tom]

The new IPC-7351 PADS library will use Layer_25 for 3D Component Modeling. There is a 1:1 scale closed polygon of the component outline on Layer_25 used exclusively for PRO-E, Solidworks, AutoCAD, etc.

Layer_25 used to be used for generating negative planes, but that went away 3 years ago when PADS introduced negative image Custom Thermal Planes which are better than the old method.

But, there are still PCB designers using Layer_25 to produce negative CAM Planes and the 2D-Line for the component outline has absolutely no affect to that process. Designers can still use Layer_25 in the Padstack to create the Anti-pad and Thermal Relief and still use the 3D-Model feature in the new IPC-7351 PADS library. No problem, it's already been tested and proven.

[petehouwen]

there are still PCB designers using Layer_25 to produce negative CAM Planes

(I'm one of them)

that went away 3 years ago when PADS introduced negative image Custom Thermal Planes

Are you talking about the ability to define thermal definitions in the padstacks? Or is there something else that I'm missing. To be honest, I really never connected the two, after so many years of being conditioned to using layer 25.


We are still using negative CAM planes, not for the file size (although that's a plus) or to eliminate the constant reflooding (lthough that's a plus) but because it gives us better plane coverage on dense designs, and it's easier for the board houses.

[Tom]

When PADS released V4.0 the Custom Thermal Plane (which is the replacement for the Layer_25 CAM Plane) was introduced.

Before V4.0 whenever you built a through hole part Layer_25 would automatically appear in the padstack. For V4.0 forward, when you build a new through hole part, Layer_25 does not appear in the default padstack. You have to go out of your way to add it.

Yes, you define the Anti-pad and the Thermal pattern in the Padstack.

The User determines the Thermal Relief Inside Diameter, Outside Diameter, Thermal Spoke Width and Anti-pad plane clearance making the Custom Thermal Negative Plane a much better alternative than the old Layer_25 CAM Plane.

See picture below.....

[Colorado-PC-Dude]

A custom thermal for positive planes would also be a good idea. Will there be/when will the wish list be out this year?

Ben

[Tom]

Ben,

That's the beauty of Custom Thermal Planes. They work with both Positive and Negative Planes. The Positive Plane has to be a Split/Mixed Plane (not a Copper Pour).

Here's an application:

You have 4 plane layers in your design. Three of the planes have only one net each assigned and one of the planes has 5 nets assigned.

The three planes with only one net become Custom Thermal Negative Planes and the one plane with 5 nets becomes a Split/Mixed Positive Plane.

All the planes will get their Thermal Data from the PADS Style built into the padstack.

You do have to unselect one box in Setup / Preferences. See picture below....

[Colorado-PC-Dude]

That's all well and good, but for those of us who use copper pour (we only rarely have more than +5 and GND planes) we're stuck with standard thermals.

Ben

[PRoehl]

Hey Ben,

Even if you only have one voltage per plane layer, you can still set the layer as a split/mixed plane. You just don't split it. Then you can use all the functionality of the split/mixed planes. I'm not sure if you had thought about that before?

Go Jake!

[petehouwen]

If you aren't splitting planes, CAM planes are worth looking into. They're much easier.