Low ohmic shunt resistor direct on PCB copper layer

Making PCB Layouts, Manual routing, Auto-routing, Copper pouring, Updating from Schematic, Manufacturing Output
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ulfjar
Posts: 8
Joined: 26 Aug 2014, 10:13

Low ohmic shunt resistor direct on PCB copper layer

#1 Post by ulfjar » 05 Jun 2017, 17:06

I want to create a low ohmic shunt resistor (current sense) direct on the PCB's copper layer.
I need to create 100 mohm +/-10% and 50 mohm +/-10% resistor.
With 35 um thick copper layer, 0,2 mm wide wire, 30 celsius I have estimated the wire length to ~40 mm (100mohm) and ~20 mm (50 mohm)

Any suggestions of a working solution in DipTrace ?

I have try to do the resistor in the "Pattern Editor" (on Top Layer) and this works, but when a use "Verification"/"Check design rules" in the "PCB Layout" program I got many, many errors....
In my PCB design I use over 50 shunt-resistors and then I got hundreds of errors just for the shunt resistors, so it almost impossible to found other real errors on my PCB board.

I also try to do the resistor direct in the "PCB Layout" program, but the resistors are shorted when I add the copper pour :-( ...of course....:-(
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Tomg
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Posts: 1740
Joined: 20 Jun 2015, 14:39

Re: Low ohmic shunt resistor direct on PCB copper layer

#2 Post by Tomg » 07 Jun 2017, 14:00

You can create a single "squiggly pad" in the Pattern Editor that should not run afoul of the DRC and/or copper pours in the PCB Layout editor. However, a problem arises when trying to create a component for the single-pad pattern in the Component Editor, which really needs two pads to make any sense in the schematic drawing. Connecting both pins to the same pad in the Component Editor will not play well with the Net structure when running the Renew Layout from Schematic tool. There have been numerous requests for a special Pattern Editor trace, but nothing has come of it. Here is a related thread - http://www.diptrace.com/forum/viewtopic.php?f=8&t=11095.
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Alex
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Posts: 3502
Joined: 14 Jun 2010, 06:43

Re: Low ohmic shunt resistor direct on PCB copper layer

#3 Post by Alex » 08 Jun 2017, 04:48

DRC errors appear in PCB Layout because pattern's shapes touch to each other but they are not connected to any net. You can upgroup the pattern in PCB Layout, open each shape properties and assign a net for them. DRC errors should disappear.

Polygonal pad is not the best solution because input and output traces will tend to connect to pad center.

ulfjar
Posts: 8
Joined: 26 Aug 2014, 10:13

Re: Low ohmic shunt resistor direct on PCB copper layer

#4 Post by ulfjar » 20 Jun 2017, 09:15

I "Ungroup" the pattern and create a new "net_R" for the resistor and reconnect every Cu-line to the new "net_R".
Still, I got 4 error per resistors in "Check design rules"....still it's too many errors to be comfortable.
I got two errors at each end-points of the resistor where the new resistor net "net_R" meets the original net.
Now I couldn't update the PCB with a modified schematics without several problems, but it's okey if I "Lock" the resistor pattern on the PCB-layout.
But, then I got other types of verification error in the "Check net connectivity" and " Compare with schematics".
Ok, I give up to solve this problem :-(
I solve the problem, by buying expensive low ohmic metal foil shunt resistor with a extra cost of ~$5/PCB-board.

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KevinA
Posts: 564
Joined: 18 Dec 2015, 15:35

Re: Low ohmic shunt resistor direct on PCB copper layer

#5 Post by KevinA » 20 Jun 2017, 18:32

Would it work by adding a 0603 resistor to one end of your pattern and using a 0 ohm resistor, they cost nothing.

Tried it:
Image
And 3D
Image
No errors

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