On top of the "Net to Net" view, you can find two drop down menus to select two nets, which have to be analysed. The buttons on the right side of the drop down menu may be used to automatically fill the drop down menu with corresponding nets you are currently selecting on the board design.

If you are using the button in the "Net Group to Net Group" tab, the button click will set the net group name (the net has to be included in a net group).

The options "outer/inner distance" and "Allow creepage flow via the board outline/ routings" (below) are the most important ones.

Allow creepage flow via the board outline/ routings

This option allows the calculation to consider the board outline and routings. So using this option, it allows to check inter layer distances as well.

 

 

NOTE: This option is the main difference to the "Net Groups" calculation, where only distances between nets for each layer separately are calculated.

Outer Distance & Inner Distance (max values)

To decide the proper distance, you have to consider the important parameters for the calculation. 

These parameters are:

• Voltage of the net
• Material Group
• Pollution degree

To connect these parameters there are several tables in the internet. The following image shows an example table.

Using tables like this, it is much easier to decide the proper distances for your cases.

For example:

Known

• The net has max. 400V.

Assumption

• Pollution degree = 1 on the inner layer
• Pollution degree = 3 material group II on the outer layers

With these three parameters, it is easy to get the "Inner Distance" of 1.0 mm and the "Outer Distance" of 5.6 mm.

As shown in the picture above, the corresponding DIN Standard in this example is DIN EN 60664-1.

At the bottom of the main view image there are further options.

Outline Calculation Precision

If a creepage flow is possible using the board outline, it has to be calculated in small iterations. A line or arc could be mathematically described in nearly infinite points connected by small lines. We have to limit the amount of points, so that the calculation for the shortest way can be finished within an acceptable time. In order to determine the amount of points (granularity), there are the parameters "Tolerance Lines" and "Tolerance Arc", after which distance lines and arcs are to be divided into points. The figure below illustrates this procedure.

Maximum creepage flow steps

The "maximum creepage flow steps" option allows you to influence the calculation directly. This number defines the number of steps the creepage flow is allowed to do.

For example:

You want to measure between Net/Group A and Net/Group B with a minimum acceptable distance of 5.00 mm.
With e.g. 2 allowed creepage flow steps, you allow the creepage current to go from the Net/Group A to the Net/Group B via an independent Net/Group C.
The flow distance inside the Net/Group C is not counting to the total distance, as the Net/Group C is a conducting surface. In this way, the creepage distance might be reduced compared to the direct distance between Net/Group A and Net/Group B.

So, you allow the calculation to make the creepage flow look like this:

Moves from    a Net of Group A    over   a Net of Group C    to    a Net of Group B

In this example the creepage distance between Group A and Group B is reduced from 5mm to 4mm when going over Group C elements!

Result

The image below shows a possible result of the calculation.

The following is a detailed analysis of the red marked entries. These two entries are calculated with the "Maximum creepage flow steps" of 2.

1. The first attribute of the entries shows the calculated distance. In this case it´s 3.823 mm.
2. As explained above, the calculation was done with a maximum creepage flow step count of two. The second parameter shows you the distance the creepage flow has to travel on the outer layer, combined with the percentage of this distance to the distance under test.
3. The third parameter is identical to the second parameter. The only difference is that they handle different layers. The third parameter refers only to the inner layer.
4. If the creepage flow used the PCB edge to move further, it will be shown in parameter four. Parameter four has an identical structure as the second and third parameter.
5. Parameter five visualizes the total percentage of the covered distance (this is a combined percentage of the allowed distances on outer and inner layers).
6. The following parameters are the "Net Names" and the "Layer". They will contain every net name of each net the creepage flow has used. The "Layer" parameter shows you the start layer of the creepage flow and the end.