Is there some type of non-electrical epoxy that can encase a pcb to remove heat? (something like a large heatsink(although not necessarily as good) that you can just form around a pcb?
The reason I ask is that I've seen some circuits encased in this epoxy like block(all you see is some connectors) and I'm trying to figure out if its for heat reasons or they just don't want people to get in it. (This thing is running around 20 amps max so the heat has to go somewhere)
Thanks, Jon
"Jon Slaughter" wrote in news:WU%Nj.2118$ snipped-for-privacy@newssvr22.news.prodigy.net:
encapsulation is so you can't get at it.
-- Jim Yanik jyanik at kua.net
Jon,
The power will come out regardless of the type of heatsinking (10 watts in means 10 watts out). The issue is what the component temperatures will be.
You could brute-force it and dunk the whole thing in thermal epoxy, but what a mess! 3M makes several types. I've used their TC-2810, but it's expensive.
The simplest thing to do is to identify those components that will be getting too hot and treat them individually. If you don't know how to do this then you won't be sure if any technique will solve your temperature problems (if you even have any).
Bob
-- == NOTE: I automatically delete all Google Group posts due to uncontrolled SPAM ==
So your saying that the compound has in no way anything to do with heat dissipation?
Thanks, I'll try to find some of these products and see what they do.
Copper is over 400x more thermally conductive than this stuff ;/ But maybe if its a large enough block than it wouldn't be too bad (maybe use a copper or aluminum heat sink coated in a block of this stuff? (since it is still much better than air and will help dissipate the heat from the heat sink into a larger volumn quicker)
r
Encapsulation conducts heat "better than air" if you don't take convection into account.
I worry about encapsulant holding the heat in, myself. A datasheet may give me an idea how much power a particular package can dissipate in air, but what happens with that package encased in solid glop? And make sure you don't get the device trapped inside an air bubble, then you have dead air acting as an insulator and that would kill you.
"Jon Slaughter" wrote in news:3XmOj.7455$ snipped-for-privacy@nlpi061.nbdc.sbc.com:
it probably hinders it more than it helps.
-- Jim Yanik jyanik at kua.net
No, because the air moves. Transporting hot material is the most effective way of moving heat. It's air or water usually, or sometimes liquid sodium as in nuclear reactors and the exhaust valves of racing engines.
The thermal conductivity of your average plastic is around 0.1 W/m/K, which is only 4 times higher than still air. If you have half an inch of epoxy all around the module, that's more or less equivalent to an eigth of an inch of Styrofoam. That's probably not going to improve matters.
Cheers,
Phil Hobbs
That makes no sense... if it has more thermal conductivity than air it must be better than just air alone.
Encapsulation conducts heat "better than air" if you don't take convection into account.
-- But even if it does it shouldn\'t matter too much because the block is still exposed to that convection. So the air will take heat away from the material. Now sure it matters to some degree and I might be wrong to just how much. Maybe a fan would be better. I guess one needs to know how much convection increases the thermal conductivity.
ve
if
at
e.
lled
He could use the circuit board itself as a (relatively lousy) heatsink, like using d2pak devices with the tab soldered down. FR4 conducts sideways better than straight through, but with vias he could transfer heat effectively to a copper pour on the other side of the board or internal layers.
The olde seek and ye shall find turned up a couple of links about heat management.
Jon Slaughter writes
It's generally for complying with safety regulations, usually because they're hot, or high voltage. For example you may use encapsulation in products intended for use in potentially flammable atmospheres (in petrol stations, down mines etc). However although you can choose the encapsulant to be a relatively good conductor of heat (last time I checked, silicone-based rubbery ones were best), you're still putting a heat barrier between the components and the dissipative medium (air) so although the heat eventually gets out, it does so more slowly and the components under it get a bit hotter. When forced to resort to designing encapsulated circuits, you generally end up building a sacrificial PCB, encapsulating a thermocouple probe next to the hot components, and running the thing on max load for a couple of hours to check you ain't going to overheat the devices under there.
Oh and you want the encapsulant to be UL recognised / flame retardant.
I've also seen encapsulation used in satellite electronics, to protect against the vibration and g-forces when launched. They probably use it in military stuff for the same reasons, but I don't know about that field.
-- Nemo
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.