Bus Material for SOT-227 Half-Bridge
GrantX, Thu Jun 26 2014, 07:35AMHello everyone,
I'm currently putting together a small half-bridge inverter for a SSTC (possibly DR, haven't really decided yet) using SOT-227B MOSFETs. I've currently got a pair of IXTN79N20's, but they might be swapped out for beefier devices with a higher voltage rating.
I've got a design drawn up for a little busbar network to keep stray inductances down and to make life easier when mounting all the capacitors, TVS's and zeners, but I'm not sure what material to use. Ideally, I would use copper or brass, perhaps about 1.5mm to 2mm thick, but the sheets I've found so far are enormously expensive.
I have a large amount of 3mm thick aluminium here which would be perfect, but I'm not sure if aluminium will cause problems. Will their be any issues getting a solid contact between the nickel plated terminals and the aluminium surface? Is any special surface preparation needed to get a decent electrical contact? I have a feeling the oxide layer will cause problems wherever there are joins or terminals, but I might be wrong.
Has anyone here used aluminium as a conductor successfully in a high-frequency high-current application? Should I just keep looking for affordable copper or brass?
Re: Bus Material for SOT-227 Half-Bridge
Steve Conner, Thu Jun 26 2014, 08:50AM
Well, the screw terminals on big electrolytic caps are all made of aluminium, so it can't be that bad. Also aluminium has almost 3x better electrical conductivity than brass.
For a really good job you might like to sand the oxide layer off before assembly and apply a jointing compound like Thomas & Betts Aluma-shield.
That is somewhat specialised stuff, so if you can't get it, a thin layer of copper grease or Arctic Silver thermal paste might do.
Steve Conner, Thu Jun 26 2014, 08:50AM
Well, the screw terminals on big electrolytic caps are all made of aluminium, so it can't be that bad. Also aluminium has almost 3x better electrical conductivity than brass.
For a really good job you might like to sand the oxide layer off before assembly and apply a jointing compound like Thomas & Betts Aluma-shield.
That is somewhat specialised stuff, so if you can't get it, a thin layer of copper grease or Arctic Silver thermal paste might do.Re: Bus Material for SOT-227 Half-Bridge
Dr. Dark Current, Thu Jun 26 2014, 09:57AM
It just came to my mind, would not there be problems with using copper busbars mounted to aluminum terminals of electrolytic caps?
Dr. Dark Current, Thu Jun 26 2014, 09:57AM
It just came to my mind, would not there be problems with using copper busbars mounted to aluminum terminals of electrolytic caps?
Re: Bus Material for SOT-227 Half-Bridge
Steve Conner, Thu Jun 26 2014, 11:18AM
Well, in practice they seem to work fine
The terminals may be pure aluminium rather than some sort of alloy, and they certainly won't have any surface treatment like anodising.
Steve Conner, Thu Jun 26 2014, 11:18AM
Well, in practice they seem to work fine
The terminals may be pure aluminium rather than some sort of alloy, and they certainly won't have any surface treatment like anodising.Re: Bus Material for SOT-227 Half-Bridge
GrantX, Fri Jun 27 2014, 05:41AM
Haha, I feel like a goof now. I've got some big Mallory caps in front of me which very obviously have aluminium terminals. I could have answered my own questions if I'd just looked a little closer! :) I'd just assumed brass was better due to it's copper content. You can tell I don't know much about metallurgy... or Google searching.
I guess I was just over thinking everything. I've found a couple of aluminium antioxidant pastes which are designed for electrical connections, and it looks like I can get one online at a reasonable price ($5US for about 120mL). I think I'll get some, just to ensure everything's done correctly the first time. I like working with aluminium so it'll be handy to keep around.
GrantX, Fri Jun 27 2014, 05:41AM
Steve Conner wrote ...
Well, the screw terminals on big electrolytic caps are all made of aluminium, so it can't be that bad. Also aluminium has almost 3x better electrical conductivity than brass.
For a really good job you might like to sand the oxide layer off before assembly and apply a jointing compound like Thomas & Betts Aluma-shield. That is somewhat specialised stuff, so if you can't get it, a thin layer of copper grease or Arctic Silver thermal paste might do.
Thanks for the help.Well, the screw terminals on big electrolytic caps are all made of aluminium, so it can't be that bad. Also aluminium has almost 3x better electrical conductivity than brass.
For a really good job you might like to sand the oxide layer off before assembly and apply a jointing compound like Thomas & Betts Aluma-shield.
That is somewhat specialised stuff, so if you can't get it, a thin layer of copper grease or Arctic Silver thermal paste might do.Haha, I feel like a goof now. I've got some big Mallory caps in front of me which very obviously have aluminium terminals. I could have answered my own questions if I'd just looked a little closer! :) I'd just assumed brass was better due to it's copper content. You can tell I don't know much about metallurgy... or Google searching.
I guess I was just over thinking everything. I've found a couple of aluminium antioxidant pastes which are designed for electrical connections, and it looks like I can get one online at a reasonable price ($5US for about 120mL). I think I'll get some, just to ensure everything's done correctly the first time. I like working with aluminium so it'll be handy to keep around.
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