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copper clad thickness for full bridge

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StevenCaton

Tue Jan 06 2009, 03:10AM

Registered Member #1845 Joined: Fri Dec 05 2008, 05:38AM
Location: California
Posts: 211

I am building a SSTC with a full bridge of IRFP260 MOSFETS. I am building the full bridge on a copper clad board.
I ordered a board that has 1/64 of an inch of copper on it.

Is 1/64 inches too thin?

I know the width of the traces obviously makes a difference, but assuming that the traces probably wont be larger than 3/16 of an inch in some spots, is the thickness too thin?

teslacoolguy

Tue Jan 06 2009, 03:49AM

Registered Member #1107 Joined: Thu Nov 08 2007, 10:09PM
Location:
Posts: 792

If you are concerned about current carrying capability then just take solder and make a nice thick bead on the traces.

StevenCaton

Tue Jan 06 2009, 04:07AM

Registered Member #1845 Joined: Fri Dec 05 2008, 05:38AM
Location: California
Posts: 211

I would rather just do it with a good thickness (which I don't know) and not have to waste a whole bunch of solder.

Herr Zapp

Tue Jan 06 2009, 06:23AM

Registered Member #480 Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644

Teslacoolguy -

With conventional tin-lead solder having a conductivity of about 10-12% of copper, just adding a thick layer of solder on top of a trace doesn't accomplish much.

When the solder is just a few thousandths of an inch thick, like around a component lead passing through a plated through-hole in a circuit board, or under a surface-mount component, the resistivity doesn't really have much effect. However, as soon as you start trying to make it into a conductor with any length, the resistivity does become a large factor.

If you need more current carrying capacity in your PCBA, use wider traces or thicker copper.

Regards,
Herr Zapp

hvguy

Tue Jan 06 2009, 08:02AM

Registered Member #289 Joined: Mon Mar 06 2006, 10:45AM
Location: Conroe, TX
Posts: 154

A few methods I use when PCBs need to cary current:

Thicker trace

Trace on both sides of PCB (connect with vias)

Solder a piece of copper wire/strap to the trace

Bolt a piece of copper bar to the PCB (for really high power stuff, overkill for a small SSTC)

Don't use PCB and connect with wire instead

Tinning is better than nothing should it be necessary. It may not reduce the trace resistance much but it does substantially increase the traces heat capacity. This really helps on short duty cycle devices like SSTCs.

Sulaiman

Tue Jan 06 2009, 09:59AM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

No matter how thick the copper cladding is, (within the limits of most currently manufactured boards)
with high-power electronics there comes a point where high-current paths need either a wire link or a copper strip or bus.
Manufacturers often use stamped copper strips as high current links but for amateur use I'd just use wire.
My own favourite is solid tinned copper wire, don't try to attach it along the copper - too complicated,
just 'jumper' point to point, preferably on the component side for a single-sided pcb to reduce the risks of short-circuits.

For my own prototyping I use plain matrix board and join point to point with tinned copper wire.
Takes less time than designing/fabricating a pcb - that always needs changing anyway.
(for rf prototyping I like 'ugly' and 'manhattan' style prototyping, and sometimes plain matrix and wire.)

HV Enthusiast

Tue Jan 06 2009, 12:22PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

1/64" copper is really thick. Thats equivalent to about 11 oz copper. Your typical off-the-shelf PCB boards are 1 oz. copper.

Actually, seeing your bridge is full of IRFP260 MOSFETs, 11 oz. copper is WAAAAAYYYYY overkill, so you have nothing to worry about.

Just use big area fills (top and bottom if possible) for your current traces.

Proud Mary

Tue Jan 06 2009, 12:35PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

As Sulaiman says, I'd go with point-to-point wiring every time for heavy currents.

In any case, why use PCB board at all? Printed circuits are first and foremost a technique of automated mass production - an economic technique or business method - which does not mean they are necessarily the best or most effective way of turning any particular circuit diagram into reality.

HV Enthusiast

Tue Jan 06 2009, 01:36PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

Harry wrote ...

As Sulaiman says, I'd go with point-to-point wiring every time for heavy currents.

In any case, why use PCB board at all? Printed circuits are first and foremost a technique of automated mass production - an economic technique or business method - which does not mean they are necessarily the best or most effective way of turning any particular circuit diagram into reality.

A PCB board is SUPERIOR when dealing with power circuits with high pulsed currents. Inductance can be more tightly controlled and minimized with a PCB board (tight coupling between top and bottom - if routed properly) than using point to point wiring.

Point-to-point wiring is fine for DC, but with high frequency and in particular high current (particularly pulsed applications), PCB board trumps point-to-point wiring every time.

Point-to-Point wiring just asks for large current loops. Probably not a big deal with a regular SSTC, but when you get into higher power DRSSTCs, etc..., the amount of inductance created by point-to-point wiring has the potential to be very bad.

Of course, you have to make sure you route and layout everything correctly to take advantage of the layer to layer coupling.

Tom540

Tue Jan 06 2009, 06:08PM

Banned on 3/17/2009.
Registered Member #487 Joined: Sun Jul 09 2006, 01:22AM
Location:
Posts: 617

Not to be redundant or anything but 1 or 2 ounce copper is plenty for an sstc and if you want like Dan said double the layers and stitch them with vias. My sstc and DRSSTC bridge boards are 1oz copper with all power traces doubled up on two layers. As far as trace width you can search a chart on google. Use pours where ever possible. That will tell you the width you should use for how much current you are handling and what trace temperature.

At my last job we had boards that were 4oz copper that were designed to handle 80 amps of continuous current. Anything over 2 oz is not only overkill but will cost you a lot of money. Heres an example. 1 oz copper doubled up on two layers.

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