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I'm designing a PCB which needs to handle high currents across various fuses, relays and connectors. The current ratings would be 8A, 20A, 50A, 80A. So I would like to know which is best approach to handle such currents considering the temperature and losses. I'm sure massive traces are needed to do this and which is not possible as I'm using Mentor Graphics PADS 9.5 in which the max trace width I can get is 0.25mil. Also heard of copper pours and planes but not exactly sure how to approach.

If anyone have come across such thing and had practical experience. Please let me know.

Thank you

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    \$\begingroup\$ Do you really mean 0.25mil, 0.00025 inch, trace width? My calculator says that is 0.00635mm. That is extremely narrow. Or do you mean 0.25mm? \$\endgroup\$ – gbulmer Sep 24 '16 at 16:34
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    \$\begingroup\$ Voltage (differences) are across, currents are through. \$\endgroup\$ – Andrew Morton Sep 24 '16 at 16:37
  • \$\begingroup\$ Related: electronics.stackexchange.com/questions/255981/… \$\endgroup\$ – Bence Kaulics Sep 24 '16 at 16:38
  • \$\begingroup\$ Not only make tracks of appropriate width, but specify "2 oz" copper (double the normal thickness) to the PCB manufacturing house. \$\endgroup\$ – Brian Drummond Sep 24 '16 at 20:38
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I can assure you that PADS 9.5 can do tracks a great deal larger then that, 0.25mil is probably not even manufacturable!

Edit the global design rules table for track width and bump it to something bigger then whatever you think you need.

For that much current I would be looking at thicker then standard copper, maybe 3 or 4 oz/square foot which will impact your minimum feature size, or maybe just soldering a copper busbar onto the board after the fact.

The advantage of the busbar is that is can be very heavy and does not impose the feature size restrictions that heavy copper plating does, a good trick here is to get the busbar stamped out of copper sheet, then paste and reflow (Vapour phase deals well with the very large heat capacity).

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I'm sure massive traces are needed to do this and which is not possible as I'm using Mentor Graphics PADS 9.5 in which the max trace width I can get is 0.25mil. Also heard of copper pours and planes but not exactly sure how to approach.

Sounds like you need to learn how to use PADs first but before that you need to understand what a copper pour is (do some googling because it's a general thing for all PCB software I believe).

Anyway, go to setup and somewhere in that menu is a sub menu and try and find a sub/sub menu called "clearance" (it may be under a sub menu called "default"). On this page you can set minimum, default and maximum track widths - more than likely this is preventing you from making the width bigger.

PADs is illogical because to set track widths you have to use the "clearance" menu and this just does not make sense to me. I'll also add that PADs is the 2nd worst piece of software I've ever used. The worst piece of software I've ever used is also made by mentalgrahics (DxD) so you have my great sympathy!

Or, it may be just you need to start a route then press w - a box will appear containing the "w" and you press spacebar then 50 - this will give you a 50 mil track width (providing it isn't constrained by my previous recommendation about going to the clearance sub menu).

If you want to draw solid copper be prepared to jump thru a few hoops. You need to be in drafting mode (I think it's called) and select the icon at the top of the screen pertaining to copper. Then right click anywhere in the design area and select rectangle. Then draw a rectangle - I think from thereon pads automatically prompts you to select the layer you want it on. If not hold the shift key and click on the box then a right mouse click will allow you to select properties.

Select the layer and then select the net you want to attach it to - there's a pull down menu of all nets and click on the one you want. To move the rectangle use shift left-mouse then CTRL-E.

Have I said how awful PADs is?

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    \$\begingroup\$ We have a phrase around the office for when PADS has just shit the bed (again), "Mentor magic moment", come back Altium all is forgiven. I have a special place in my heart for whichever crack monkey set it to only run DRC on the part of the board currently displayed (I have lost at least one board spin to that).... Andy, I dont suppose you have ever found a way to get PartLister to actually tell you when it decided to stop 90% of the way into the job? Concur about DxD, simply shocking. \$\endgroup\$ – Dan Mills Sep 24 '16 at 16:54
  • \$\begingroup\$ @DanMills it is such a pile of droppings. The DRC on connectivity however does work across the whole design (thank heavens for small mercies). I haven't used partlister. Glad you have also found DxD rewarding. See this: offlogic.wordpress.com/2009/08/12/… \$\endgroup\$ – Andy aka Sep 24 '16 at 16:55
  • \$\begingroup\$ Connectivity works, sort of, but it does not check clearances for anything off screen, so you can shove a via, forget to repour all the planes, have it pass DRC, and give you a gerber with L2 & L3 tied together.... Oh how I laughed. \$\endgroup\$ – Dan Mills Sep 24 '16 at 17:00
  • \$\begingroup\$ PADS wasn't "made" by Mentor Graphics. PADS was bought by Mentor Graphics. But it was already quite ... illogical even before then. \$\endgroup\$ – Brian Drummond Sep 24 '16 at 20:35

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