glob-top thermals

It even has its own Youtube show.

Yeah it's hard to know if a layer of 'insulation' would help. I was once thinking that several layers of heat shrink tubing around a through hole R's might allow for higher powers. And though the 'insulator/ goop' is better than still air, is it better than convection in air? Who knows, and may be orientation dependent.

I never tried the resistor + heat shrink tubing.

George H

mandag den 11. februar 2019 kl. 18.07.59 UTC+1 skrev John Larkin:

I've used them, but they are not stocked in the value I need (lots of

FWLIW I once used electrolytic caps to cool some small germanium transistors. Just tied them together. It worked :)

Dunno if you can get some copper powder in that epoxy - not too much of course.

NT

There are 1-W 0612 resistors. I'm using these ones:

R15-100H-00, RES,, FIXED, 100.0m, 1.0%, 1.0W, 100.0p, THICK, 200.0,, Wide 1206 hi pwr , 0612 , ERJ-B2CFR10V , PANASONIC , $0.1174 , 1000.0 , @EACH, DIGIKEY

Cheers

Phil

That only comes in 0.1R. The 0612 orientation does allow better conduction cooling, hot spot to end caps.

Susumu has a 1 watt 1206

but it looks like they just have more pad area. I can do that with any

There are some 0612s in my resistance range, rated 3/4 watts.

Now I'm thinking that two 0805s in parallel will be a lot better than one 1206.

Or series. Maybe you can separate them. I'm using CRCW1210-HP e3, rated 0.75W.

Good idea, series: less capacitance.

A watt for a square inch is troublesome. Surely the board MOUNTS to something, can you position the hot thing near a (heat-conductive) structural element?

It will be a baby board that surface-mounts on a bigger board.

Good tunes, too. Panacol The Disco!

Tim

Needs a bunch of copper in the middle though.

Cheers

Phil Hobbs

How about this:

That roughly multiplies the pad areas by 5x. I'm thinking that the glob-top epoxy will pull heat out of the resistors and the topside traces and spread it out some to the surface. Heat will also go down through the FR4 to the ground plane, layer 2.

Capacitances shouldn't be bad. L2 helps isolate things.

Using two 0805s spreads out the heat a bit too.

I still wonder what glob-top does to the hot spot on a resistor. Maybe I'll do the thinfilm RTD experiment, or get a scut bunny to do it.

There's a lot of copper missing on layer 1 that could remain there. And on other layers IIRC.

There needs to be a tiny heatsink one can pick & place onto those sm parts.

NT

Why not use a thermally conductive layer of glob or a thermal pad spreading the heat to a larger amount of glob. You've used thermal pads before. Bu t then I guess they need to be pressed into good contact which would requir e some sort of clamp. How about a small aluminum sheet on top mounted to y our screw holes?

================= Al Sheet ============= Thermal Pad [===] [===] Resistors ================= PWB

Yeah, instead of a very, very easy glob top that doesn't conduct well, use something a little harder that conducts very well.

Or you could use a little math to calculate the thermal conductivity of the glob top. I expect this is not a case where more is more since the conduc tivity is so poor, but the math will tell all.

Rick C.

I don't think I'd want to rely on it, because it seems likely to delaminate at some stage on account of the thermal shear stress.

The alumina substrate of the resistor is about 35 W/m/K, so going to

Maybe you could extend the pads towards the middle of the resistor and use the epoxy as underfill.

Cheers

Phil Hobbs