Frequently Asked Questions
Copper Pour Management
[ PCB Design / Poured Copper ]
The basics of pouring copper are fairly obvious, but this FAQ looks at methods of getting the best from this feature.
Firstly, a number of points to remember:
When pouring copper on a board, the pour area can lie outside the board.The poured copper will always stay within the board. This means a square pour can be used for a circular board, for example. You don't have to carefully follow the board outline or try to draw the outer edge of the copper inside the board, the algorithm will use the correct spacings to ensure the copper only goes where it is allowed.
The pour area is strictly a construction line. It won't output, and won't cause shorts, so leave it in place for future use. If you find this confusing, use [View], [Display]. The [Layers and Layer Spans] tab allows you to customise the colours used for pour areas and also hide them when required.
The line style used for the pour area is also the style used for the fill. Wider means smaller files and faster loading and redraw, but limits the gap through which the pour can flow.
Pour doesn't work well with very shallow angles. To find orthogonal tracks that aren't (which could cause problems), use the 'Angled Tracks' option on the [Settings and Highlights] tab under [View], [Display]. This will flag all tracks except arcs, or those at a multiple of 45 degrees so you can find any odd angles.
With all scenarios, you should avoid adding copper pour areas to a power plane as this can cause conflict, so remove the net name and change the layer bias before adding any pour areas.
Multiple pours on the same layer
Pours are often used because a power plane is inadequate, often because of split signals on the same layer. Where these can be made to interlock, jigsaw fashion, there's no problem, but sometimes one pour will completely surround another.
When this happens, you must turn to the properties of each pour area. There's a check box marked 'Order' which defaults to zero. This is the order in which the program attempts to pour copper, so where there are concentric pours, the central one must be assigned zero. the next pour out is changed to 1, then 2, and so on to the outermost pour. For more complex nesting, like a double yolk egg, always make sure that the pour is at least one number higher than any pours contained within it. If you think of the pour areas as contour lines for a hill, the highest point must have the lowest number.
Gaps and Keepouts
Even this does not cover all possibilities. Consider where you want a clear space within a pour, perhaps because capacitively sensitive signals are present in that area. You need something to prevent pour in a defined area.
To do this, add another pour area round the profile, then open the properties for this pour area. Check the box marked 'Pour Keepout' and you've created a void. The net name for this keepout can either be left blank, or matched to the same net as the outer pour area. This changes the behaviour in a subtle way. Leaving the net blank ensures that no copper will be poured for any net within the keepout area, but entering a net name restricts the effect of the keepout to that net only, allowing other nets to be nested into the keepout.
There's still one other case which at first sight seems insoluble. That's where concentric pours need to be nested, but with a gap between them. For instance, the gap might contain a ring of high voltage circuitry. Here the keepout is useless, as it will prevent the inner area from pouring, regardless of the setting. It's necessary to fall back on a different feature.
Create the outer pour area, then select any part of it, and use 'Add', 'Cutout', selecting the best sub option to create the inner edge of the pour area. This will work whether or not the copper has already been poured. It's now possible to nest a second pour area on the same net within the space created without encountering problems. Because of the properties of the cutout, it's not even strictly necessary to use the order parameter, but it's good practice to do so anyway.
This document is intended to cover all likely scenarios. if you have one which has not been discussed here, please contact the support desk for more advice.