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Overlapping Pads in Eagle

I have two layout problems that I need to solve in Eagle, both involving high-current circuits:

First, I'm going to be laying down some FETs in SO-8 packages, and I want a good solid connection from the four drain pins to a surrounding hunk-o-copper, both for current flow and to provide a thermal path for heat sinking. For the same part I want the same solid connection to the source pins, although I don't need the copper. Connections that allow good wide traces (up to 200 mils would be nice) without stomping on the gate connection is essential, of course.

Second, I'll be putting in some current sense resistors. While I'm going cheap and using 2-terminal resistors, I'd like to make a pseudo 4- terminal device by laying the part out with four pads, but then connecting pairs of pads with a polygon or some such so that it looks and solders like a regular resistor, but so that I can have my nice high- current connections going to it with honkin' big traces, and still have some thin traces coming off of the pads -- independent of the big traces

-- in a "pseudo Kelvin" connection.

Has anyone solved this problem before? Got any suggestions on how to proceed?

--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?

Tim Wescott, Communications, Control, Circuits & Software
http://www.wescottdesign.com
Reply to
Tim Wescott
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Does Eagle have a Net Bridge/Tie feature? In Altium at least, you can specify that a component can be allowed to have copper bridging between pads in different nets. This allows one to implement printed components (inductors, transformers, antennas, stripline, etc.) from a standard schematic, without upsetting the DRC.

Tim

-- Deep Friar: a very philosophical monk. Website:

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Reply to
Tim Williams

I do a manual route for current sense resistors, to get an accurate voltage reading. Route the current path first then manually route the sense traces. You don't need a 4 terminal footprint.

Cheers

Reply to
Martin Riddle

The four terminal footprint is specifically to make autorouting and design rule checking easier. Even if I don't autoroute, I'd still like to have a DRC find too-thin current-carrying traces, without dinging me for having thin traces to the sense amp.

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com
Reply to
Tim Wescott

OK, if you create the footprint with a poly over 2 terminals, the DRC shouldn't complain.

Cheers

Reply to
Martin Riddle

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