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I would like to read more about this technology, I'm looking for a suitable book now. I want to use this technology to prepare (electically isolate) heatsinks for power transistors.
I will build a full-bridge power supply (bipolar capable) and a simple spectrum analyzer. The latter one to quantify the temperature of the sparks - a vital process parameter.
Any hints and tips, other experiences or similar, are warmly welcome :)
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
nice videos I doubt that a book will help compared to internet resources.
Often the most useful resources are manufacturers data, instructions, application notes etc. as they want their customers to succed.
If I understand correctly, a porous layer will be formed which would not guarantee electrical isolation if moisture is present so use as insulation for heatsinks may not be reliable especially if the protective layer is scratched during installation.
If you watch the second video, even after the protective layer has formed small nebulous discharges can still be seen which implies to me that the protective layer is not ideal.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
There are also the old 'wet chemistry' anodizing methods as well, some of which can build up quite thick layers of oxide. These are generally porous as well, allowing them to hold a 'dye'. I just mention this as there 'may' be alternatives to 'plasma processing' that might achieve similar results.
Still, process parameters are not discussed wrt heatsinks. Same as Keronite. They know how to protect and profit from their immaterial findings.
As the surface is very hard (from 1000 HV to 2000 HV), I don't think scratching is a problem during installation. Post installation ohmic test will quickly tell if the insulation is good or not. I've dabbed some with anodizing, some heatsinks are perfect with GOhms of resistance, others come in at low kOhms.
@Ash. The main pro with this method is the lack of sulfuric acid. It corrodes everything around it. But yes, hard anodizing are absolutely suitable for heatsink insulation.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
Storken wrote ...
@Ash. The main pro with this method is the lack of sulfuric acid. It corrodes everything around it. But yes, hard anodizing are absolutely suitable for heatsink insulation.
It's a while since I looked into this myself, that's why I've not posted any details, but I do remember that there are loads of different 'recipes', some just use sodium bicarbonate, if I remember correctly (although this doesn't give 'hard' anodizing). I imagine there will be some 'hard anodizing' recipes that don't use sulphuric, although I'm not certain, I'd have to refresh my memory.
EDIT: just looked on Wikipedia, and it says anodizing with borate or tartrate produces a non-porous coating:
"Borate and tartrate baths
Anodizing can also be performed in borate or tartrate baths in which aluminium oxide is insoluble. In these processes, the coating growth stops when the part is fully covered, and the thickness is linearly related to the voltage applied. These coatings are free of pores, relative to the sulfuric and chromic acid processes. This type of coating is widely used to make electrolytic capacitors, because the thin aluminium films (typically less than 0.5 μm) would risk being pierced by acidic processes."
If it's used for capacitors it 'may' be suitable for your application, although it doesn't say how hard it is, but thickness is voltage dependant.
I'm currently reading through this: ]taleb_kaled_h_x.pdf[/file]
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
Patrick wrote ...
Is any of this easier and cheaper than using the normal stick'em thermal pads. Or mica?
I'm guessing the idea is that it should conduct more heat than thermal pads, but I'm only guessing here. Whether or not it works out any cheaper would probably depend on quantity, but I'm only guessing again. The process I've linked to and which is described in the pdf I posted doesn't look that difficult, although preparation and cleanliness, as with most electrochemical processes is vital.
I'm interested enough to try this myself, pharmaceutical grade boric acid and borax are easy enough to get hold of.
I've not looked to deeply into what's involved in the plasma process that Storken posted, though.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
im going out on a limb here, but going to say that spark/plasma forming l must be more difficult than electrolytic deposition (like capacitor plates, as others mentioned.) and more difficult to quality control.
just my opinion, but the aqueous-electrolytic method looks easier and more reliable. and youll still get to choose the shape of the deposition area.
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