Thermally conductive adhesive

[John Devereux]

[...]

We do actually have an aluminium block too, but it is mainly coupled
to the groundplane rather than the LED itself (because of
manufacturing tolerances). Fixed pitch font:


. | LED
. V
.
. _
. [XXXXXXX]| |[XXXXXXX] <--- 5mm Aluminium plate
.PCB =========================================
.
.

There are some vertical screws clamping the whole thing up to the
metal block of the product.

The critical thing is to cool the baseplate of the LED, so the thermal
interface to the groundplane is what I was concerned about.

I am liking Spheros idea of mounting it from behind the board more and
more:

. [XXXXXXX] _ [XXXXXXX] <--- 5mm Aluminium plate
.PCB ===================| |=====================
. `' `'

We could put some bolt heads either side of the led base to clamp
everything up really solidly without needing any adhesive. We would
need to carefully trim the anode lead and bend it around to a solder
pad. The cathode could just be be snipped off. A bit labour intensive,
but much better than gluing.

A nice, large annular ring plated thru hole IS a very nice way to mount
it. If that is your choice, you should also surround that hole with some
cladding

Not sure what you mean by "cladding"?

and add some smaller plated thru holes as they increase the thermal
mass of the PCB and make it conduct heat better Then you could place
little heat radiators 'posts' into the other holes on the underside
of the board and air currents can carry a lot of the heat away from
the PCB.

Could do - we have a lot of vias already, and I think those combined
with the Aluminium plate should be more than sufficient!

 

[John Devereux]

Every think of using an IR laser diode? Definite spot, and lower power
needs. Maybe a couple more components.

We have used lasers for this on other versions.

They do have other problems. Amplitude noise from mode jumps, speckle
and etalon fringes, limited temperature range, ESD sensitivity,
external collimator).

As well as many admirable characteristics of course.

 

[John Devereux]

I forgot, you can also solder down a bit of sheet copper on the top
side.

It is also worth, filling the holes. Nearly any material is a better
thermal conductor than air.

We did that too! Had a big dense grid of vias then ran it through the
wave solder machine. Unfortunately you then often get little bumps
that interfere with the aluminium plate the board is bolted
against... I decided we needed good thermal contact with that plate
more than the filled vias.

We can spend forever tinkering with this sort of thing... what if we
tent solder resist over the holes on one side, what if we put the
plate on before wave soldering, etc. But it's all overkill, all we
really need do it get the heat away from the immediate vicinity of the
led base, which just requires good thermal contact with the
groundplane.

 

[John Devereux]

Like a shield or ground plane. COPPER.

In other words, an entire area of copper between an array of smaller
plated thru holes that surround the one, large, plated thru mounting
hole

OK, we do have actual ground planes (both sides) with lots of vias
surrounding the led area, as described in another post.

We use the same idea for cooling SMT transistors. I'll hunt up a pic
of a 15kV miniature supply (you could fit 6 in a pack of cigs) that has a
real nice heat management around an SMT transistor package. I have to
hunt up the pic tho.

"cool".

 

[David Lesher]

On Tue, 3 Mar 2009 03:15:10 +0000 (UTC), David Lesher

There is an LM35 in a TO220 package, which can be handy.

But as I recall; all the metal packages were non-isolated. I didn't need
fast response so I just tolerated the resistance. (I was measuring water
pipe temps in a home hydronic floor system.)

 

[John Devereux]

Gosh, i have seen lots of stuff like that. Many with more fins / fin
area.

Sure, I've seen the finned springy ones, but not that specific type.

It looked like I could have used it in conjuction with our aluminium
plate.

[...]

We do actually have an aluminium block too, but it is mainly coupled
to the groundplane rather than the LED itself (because of
manufacturing tolerances). Fixed pitch font:


. | LED
. V
.
. _
. [XXXXXXX]| |[XXXXXXX] <--- 5mm Aluminium plate
.PCB =========================================
.
.

[...]