Reducing Copper Trance Resistances, ideas?

You can use PCB solder-on busbars. Or buy boards with seriously thick copper, $$$ from Bergquist etc.

Den onsdag den 12. november 2014 23.37.09 UTC+1 skrev Klaus Kragelund:

I'm not sure inner layers add so much

how about something like this?

-Lasse

At GenRad we had bus bars with multi-thru-hole pins. Don't remember what they were called. ...Jim Thompson

The heat doesn't get out very well, but paralleling traces on multiple layers is a way to get the resistance down, given a constraint of, say, 2 oz copper.

There are the classic PCB bus bars....

What frequency? High enough to produce skin effects?

Sylvia.

Or delete the solder mask over the high-current traces and wave-solder them to add thickness. Solder has about 10%-20% the conductivity of copper, so you need quite a bit to make much of a difference, but every little helps.

Cheers

Phil Hobbs

• Adding a metal that is known to have higher resistivity and whisker generation? Insane. Think of a "3-D" board, where those particular "traces" are solid copper with the thickness of your 4 or 6-layer board; that technology has been around for well over 5 years. What added layers gives might be more copper cross-sectional area, but will also give excellent thermal insulation of the traces. For that to be productive,the thickness of the traces is the key, given fixed trace width. Back up one step and do some BOE thermal calculations for "minimum" cross-sectional I*I*R dissipation with given insulation/cooling. Air is not a good thermal conductor, BUT it does tend to move when heated for convected cooling. PCB material is just a thermal insulator here.

From what little you have said, it would seem you need at least 4 times the cross-sectional copper area if other thermal characteristics are not altered.

Alternate to a 3-D board, try no power traces and use copper heat pipe to external finned radiator.

They might have something for you:

Topside, solder paste and reflow.

That's nice. Would need something like 50 of those, since the PCB is 200x300 mm

Regards

Klaus

The mains frequency is 50Hz and the switching frequency for the motor is sub 20kHz, so the skin depth is something like 500um, so even if we calculate for 3rd and 5th harmonics, we still do not have a lot of current displacement

Regards

Klaus

We are using 2oz, thats the maximum since we have mixed in fine pitch devices

Those are nice, have used them before :-)

Regards

Klaus

Yes, I saw a link (EEblog), which stated typically a 50% reduction of the resistance, but ofcourse that depends on what production equipment is used (but it's free)

Thanks

Klaus

I really don't know BOE calculation, what is that?

I used mathcad, plotted in all the traces and layers and respective currents and calculated total power loss of the copper traces to 30W (4 layer 35u/70u stackup). We then changed to 4 layer 35u/105u stackup and reduced the power dissipation by about 7W.

We have the option to go to 6 layers, but the price of the PCB goes up by 20% (was allready increased by 20% due to 105u), so I would like to investigate alternative solutions before I go down that path

We have about 25A RMS running in the traces, both on the mains and on the motor side

Thanks

Klaus

Yes, that is also a good option

Thanks

Klaus

There is such as thing as "extreme copper" for PCB, e.g.

I like the bus bars John linked, but I needed some a few years ago and couldn't find any that were standard, off-the-shelf.

An easy solution in your case might be adding short, bare copper jumper wires (tinned) as thru-hole components on your board.

.-----. .------. .------. .-------. .------. .------. .-----. .------. .------.

That's done to bolster the heavy battery-current traces on uninterruptible power supplies for personal computers. Putting the jumpers on the bottom and wave soldering is even better.

Cheers, James Arthur

Assuming the traces are short. Otherwise the stencil might fall apart.

Cheers

Phil Hobbs

Of course, some places will make you boards with super-thick copper, like 10 ounce. You only need it on one layer. The downside is higher cost and much poorer litho control on the thick stuff.

Cheers

Phil Hobbs

ND/2264567

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Another good source for busbar is Mersen (formerly Eldre):

If your planned production is large enough a custom busbar could be the best solution.

Regards,

Glen