Electronics > Projects, Designs, and Technical Stuff
DC load using a CPU cooler
mrflibble:
--- Quote from: eneuro on October 09, 2014, 06:33:48 pm ---
--- Quote from: mrflibble on October 09, 2014, 03:21:22 am ---The issue is the cross section of the resulting thermal interface. Spot weld ==> smaller cross section (compared to soldering) ==> poorer thermal conductivity across that thermal interface.
--- End quote ---
This is not in the case when brazing method is implemented.
--- End quote ---
Well, your remark (complete with that bit you bolded for emphasis) and my reply to your remark were about spot welding. No remarks from me about brazing, since brazing is just soldering with an attitude. And as you point out, with brazing you don't get a poor cross section as with spot welding. What with it being the same kind of filler action as with boring old lower temperature soldering.
rob77:
--- Quote from: mrflibble on October 10, 2014, 03:42:10 am ---
--- Quote from: eneuro on October 09, 2014, 06:33:48 pm ---
--- Quote from: mrflibble on October 09, 2014, 03:21:22 am ---The issue is the cross section of the resulting thermal interface. Spot weld ==> smaller cross section (compared to soldering) ==> poorer thermal conductivity across that thermal interface.
--- End quote ---
This is not in the case when brazing method is implemented.
--- End quote ---
Well, your remark (complete with that bit you bolded for emphasis) and my reply to your remark were about spot welding. No remarks from me about brazing, since brazing is just soldering with an attitude. And as you point out, with brazing you don't get a poor cross section as with spot welding. What with it being the same kind of filler action as with boring old lower temperature soldering.
--- End quote ---
and actually brazing would kill the mosfets easily - the max soldering temperature for most of the components is around 300 degree celsius while brazing happens well above 400 degree celsius. so brazing is a big big NO-GO for mosfets.
eneuro:
--- Quote from: rob77 on October 11, 2014, 05:34:05 am ---so brazing is a big big NO-GO for mosfets.
--- End quote ---
Did you tested it with your own spot welder? ???
By brazing using spot welder and short high power pulses I mean something different than that :-DD
mrflibble:
@eneuro:
Just to avoid confusion, what do you mean when you say "brazing"? Essentially the same thing as soldering, but with higher temperature melting point for the filler material? Or something different that I am not aware of?
Because you mention "brazing using spot welder"? Wut? How does that work?
At any rate, as far as I am concerned for a direct join of the metal tab of say a mosfet to a heatsink:
- spot weld ==> noooope, crap cross section ==> poor conductivity
- brazing ==> noooope, high work temperature ==> high risk of killing semiconductor
- soldering ==> yup
That is not to say that I would pick soldering over boring old clamping, but it is to say that I would pick soldering as the prefered method out of the above three choices.
Unless I am missing something, in which case please explain.
eneuro:
--- Quote from: mrflibble on October 11, 2014, 07:14:22 am ---Unless I am missing something, in which case please explain.
--- End quote ---
I wrote about those instructions in post #118 ;)
I found there How to Spot Weld Copper those instructions, and applying brazing in 1st step is a key to do it.
--- Quote ---"Instructions:
1 Apply brazing paste in between the two points to which you will apply the electrodes of the spot welder.
2 Lower the electrodes of your spot welder and pinch the two pieces of copper you will spot weld.
3 Activate your spot welder for quick bursts, turning the welder off and removing the electrodes after each burst."
--- End quote ---
Didn't tested it yet, but makes sense.
Brazing pase between two much better conductors should behave like this steel ball, but it will be diffrent thanks to point #3 of those instructions above and I have much more power full spot welder I think.
Paste should be melted quickly and since datasheet of one of mosfets I used says about 300*C for 10 seconds it is a lot of time to glue two pieces of copper.
Probably at the end of next week I will make some experiments-using spot welder with brazing pase to join together good conductors like copper and aluminium. :-/O
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