Kelvin connection or different ground connection

Question

Hello,

I have a suggestion that could help us when we route kelvin connections or when we have to connect 2 separates ground planes in only one point ("star" connection). For example when we had to connect two ground GND-logic and GND_ANALOG in one point only under the ADC....

For this kind of situation, even if all connexions must be connected together, some of them play different roles and could have different parameters (minimum width for kelvin connection).

Today I only found 2 ways for doing this:

1) On a schematic side, I use one single net (same name). With this approach, on the board side, Eagle consider that all must be electrically connected. That is gread for DRC, but I have to manually check that the separation is correctly done, and some time I must add cutoff polygon (specially for GND planes). I also have no possibility to define different min width (same net = same class), ....

2) Or I use 2 different nets, and a "kelvin connection part" that I have build in my library. Finally Eagle consider the 2 sides of this component as 2 different nets. Great, BUT, DRC is not really happy when I connect, the 2 nets with a manually added copper polygon or wire.

That I'm suggesting is:

I think that the best approach is to consider that we used different nets (different names) that we connect together with one special component. In schematic, these nets are totally independent (as in my solution 2). In broad, the package associated to this component would be a special package, that we can placed and locked like the other packages. But this package will take the form of a polygon (or at least a rectangle), We simply place this polygon (or rectangle) exactly where we want the connection of these 2 nets. This special polygon, will simple indicate to EAGLE (DRC and auto-router) that in this area and in this area only, these 2 nets must be proceed as only one net. The polygon let us decide the form of the connection.

In this way, it's easy to separate the 2 signals in schematic and in board. In the board we can decide where and how the connection is made. The DRC don't report any stupids error. And the DRC check the separation (isolate, with,...) of the to net, except under our special component.

Guillaume Barrey

autodeskguest · Answer

Guillaume barrey wrote on Mon, 19 May 2014 12:56 First problem and major one, DRC will report overlaps and clearance errors. In the case of the SHORT_ALL-50 Pachage (from SHORT.lbr) it's 4 overlaps errors per outer layers and 1 clearance error per inner layer) so 14 errors for a 6 layers. I'm designing a 6 layer board with 12 kelvin connections + one link between 2 GND... I let you do the math... Yup, that's a pain. There is a long standing request to be able to define in the package whether the DRC should flag overlap and clearance errors within a package. Quote: Ok it's possible to approve errors... But, each time you move one of these the package, the errors will appear again. Right, so don't do that. Generally the workflow is to do all placement, then routing. Occassionaly you do want to move something around as you see issues in placement, but that should be limited. If you find yourself moving things a lot, then you should start by doing a better job of placement next time. Quote: like symbol in a schematic, I don't want to have all these kinds of component in the BOM. From the SHORT_ALL-50 name of one of the shorts, this seems to be my shorts library that someone uploaded to the CadSoft web site. If so, these devices will already have a BOM attribute with value "no". Take a look. That's how my automatic BOM generation system knows to not include these shorts in the BOM. If this attribute isn't set, then either it's someone else's library or a very old version of mine. You can get my latest version at http://www.embedinc.com/pic/dload.htm . -- Web access to CadSoft support forums at www.eaglecentral.ca. Where the CadSoft EAGLE community meets.