Heatsink Fin Attachment - Epoxy vs Braze
Heatsink Fin Attachment - Epoxy vs Braze
(OP)
I'm investigating the trade-offs between bonding fins to a heatsink using thermally conductive epoxy or brazing. The epoxy is desirable because of cost but I need to verify that it can withstand exposure to jet fuel and chemical solvents on a Navy ship. I have a few epoxies that claim resistance to jet fuel but they are not thermally conductive. The thermally conductive epoxies I've found do not have data regarding chemical resistance to jet fuel. I have heard that the filler materials to improve conductivity REDUCE chemical resistance, is this true?





RE: Heatsink Fin Attachment - Epoxy vs Braze
What the filler may do is help the fuel to penetrate into the epoxy along the filler/epoxy interface. This occurs in cases where the polymer does not wet the filler properly (I have some data to show that). When the polymer wets the filler then it actually retards ingress of liquids (lower permeability). So, in conclusion I think that the filled epoxy has a good chance, always worth doing tests to make sure though.
Dow Corning sell silicone thermal compound and they may have some advice on the chemical resistance of the adhesive.
There is not any memory with less satisfaction than the memory of some temptation we resisted.
- James Branch Cabell
RE: Heatsink Fin Attachment - Epoxy vs Braze
Mike Halloran
Pembroke Pines, FL, USA
RE: Heatsink Fin Attachment - Epoxy vs Braze
I would stick with bronze on this one.
Regards
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RE: Heatsink Fin Attachment - Epoxy vs Braze
RE: Heatsink Fin Attachment - Epoxy vs Braze
There is not any memory with less satisfaction than the memory of some temptation we resisted.
- James Branch Cabell
RE: Heatsink Fin Attachment - Epoxy vs Braze
Excuse me for being thick, but how can brazing be more expensive than epoxy?
imho, (and I've been in plastics for 20-odd years) I would not even consider epoxy, heat conductive or not!
I would suggest brazing is the "only" way to go.
(esp. regarding MikeHalloran's comments!!)
Cheers
Harry
RE: Heatsink Fin Attachment - Epoxy vs Braze
Regards
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Heatsink Fin Attachment - Epoxy vs Braze
Thermal conductivity of some solids
Alumina - 30 W/mk
Brazing rod - 145 W/mk
But this is not the whole story becasue the thermal conductivity of the epoxy/with alumina flake will be nothing like that of alumina, because very little the bits of alumina in the resin will be in good contact, even silver loaded epoxy only has a thermal conductivity of about 8 W/mk compared with solid silver at about 400 W/mk, you can see that adding highly thermal conductive materials to epoxy only gives a small rise in overall thermal conductivity.
So as a total luddite I would go for the brazing for sure.
RE: Heatsink Fin Attachment - Epoxy vs Braze
The reason I mentioned alumina, boron nitride and metals is that I understand those are the ones normally used in thermal compounds.
There is not any memory with less satisfaction than the memory of some temptation we resisted.
- James Branch Cabell
RE: Heatsink Fin Attachment - Epoxy vs Braze
Many years ago I did some lab research on cooling and we found that we acheived similar rates of cooling (using a fan - forced convection)on a flat aluminium plate, with no fins, as with fins installed with silver loaded epoxy. When we welded fins on using lumiweld (a type of aluminium brazing - cheap and easy)the cooling rate went through the roof.
The experiments may have been flawed, I am only a lowly materials engineer, but I do not think so. If you accept these results then gluing fins on is a waste of time, you may as well just blow a fan over your existing surface..... Back to being a luddite.
LOL
Toys19