heat sink attaching

[David Lesher]

I need to add a heatsink to a small product. It has a flat exposed flush
heatsink now; I'm extending with fins.

But the attachment is an issue. Do the pads you put between a CPU & heatsink
provide any stick? Or are the depending on external pressure to compress
them? [I have no way to do that...]

For the record, this is a Mobius camera.
<http://www.techmoan.com/blog/2013/7/8/the-mobius-camera-the-do-it-all-mount-anywhere-1080p-micro-c.html>

--
A host is a host from coast to coast.................wb8foz@nrk.com
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433

 

[gregz]

David Lesher <wb8foz@panix.com> wrote:

I need to add a heatsink to a small product. It has a flat exposed flush
heatsink now; I'm extending with fins.

But the attachment is an issue. Do the pads you put between a CPU & heatsink
provide any stick? Or are the depending on external pressure to compress
them? [I have no way to do that...]

For the record, this is a Mobius camera.
http://www.techmoan.com/blog/2013/7/8/the-mobius-camera-the-do-it-all-mount-anywhere-1080p-micro-c.html

What do you want to do, and why ?

Temporary or permanent ?

Pads don't usually have optimum heat transfer. Metal to metal contact is
optimum, unless surfaces are really off.

Does the camera instructions say, add heat sink ?

Greg

 

[isw]

In article
<1653131741403159805.008597zekor-comcast.net@news.eternal-september.org>
,
gregz <zekor@comcast.net> wrote:

David Lesher <wb8foz@panix.com> wrote:
I need to add a heatsink to a small product. It has a flat exposed flush
heatsink now; I'm extending with fins.

But the attachment is an issue. Do the pads you put between a CPU &
heatsink
provide any stick? Or are the depending on external pressure to compress
them? [I have no way to do that...]

For the record, this is a Mobius camera.
http://www.techmoan.com/blog/2013/7/8/the-mobius-camera-the-do-it-all-mount
-anywhere-1080p-micro-c.html


What do you want to do, and why ?

Temporary or permanent ?

Pads don't usually have optimum heat transfer. Metal to metal contact is
optimum, unless surfaces are really off.

That is contrary to everything I've ever known concerning how to couple
a heat sink to a device. Almost without exception, the surfaces are, to
use your term, "really off"; they never make contact at more than a very
few small places. The purpose of the pad, or silicone grease, is to fill
up the spaces where the metal does not touch. The pad or silicone grease
is not a very good conductor compared to copper, but it is a whole lot
better than still air, which is otherwise all that couples the heat from
one piece of metal (source) to the other (sink).

In fact, because the pads are a lot easier to apply properly than
grease, the pads usually perform a bit better.

If you really need to attach the sink to the device with an adhesive,
try RTV silicone rubber, which has nearly as good thermal performance as
silicone grease, and will not weaken with heat. Be sure to use as thin a
layer as possible.

As a very general comment, small heat sinks attached to small devices
will only provide marginal improvements. It's always surprising, when I
have done thermal calculations, to find out just how large a heat a sink
has to be, to do much good ...

Isaac

 

[David Platt]

I need to add a heatsink to a small product. It has a flat exposed flush
heatsink now; I'm extending with fins.

But the attachment is an issue. Do the pads you put between a CPU & heatsink
provide any stick? Or are the depending on external pressure to compress
them? [I have no way to do that...]

Some have "stick", some do not.

Most of the CPU-style pads for larger heatsinks and larger CPUs,
aren't intended to provide structural strength. They couldn't do so
adequately in these cases... some of the modern heatsinks weigh a good
fraction of a pound... the heatsinks come with spring-loaded retainers
which clip onto tabs on the CPU socket, or screws which mate directly
onto the motherboard. The thermal transfer pads for these CPUs are
optimized for high thermal conductivity - some of them are "phase
change" compounds which (in effect) melt the first time the CPU heats
up, and flow out to form a very thin interface layer.

Heatsinks for smaller embedded CPUs, GPUs, etc. are fairly light, and
these are often fastened using a thermal adhesive (pad, or a paste or
cream). Loctite used to sell tubes of a thermally-conductive adhesive
to use used for this purpose... likely they still do.

 

[Charlie+]

On Fri, 11 Oct 2013 04:35:15 +0000 (UTC), David Lesher
<wb8foz@panix.com> wrote as underneath :

I need to add a heatsink to a small product. It has a flat exposed flush
heatsink now; I'm extending with fins.

But the attachment is an issue. Do the pads you put between a CPU & heatsink
provide any stick? Or are the depending on external pressure to compress
them? [I have no way to do that...]

For the record, this is a Mobius camera.
http://www.techmoan.com/blog/2013/7/8/the-mobius-camera-the-do-it-all-mount-anywhere-1080p-micro-c.html

Pads normally require mechanical pressure permanently.
You can use epoxy resin as long as the layer is thin and you prepare the
surfaces for mechanical key. Used this method on componants running
too hot to last! Fast set epoxy is better because it never quite seems
to set as rock solid as slow cure and thus shouldnt shatter under shock.
C+

 

[Phil Allison]

"David Lesher"

I need to add a heatsink to a small product. It has a flat exposed flush
heatsink now; I'm extending with fins.

But the attachment is an issue.

** Suggest you lightly sand the mating surfaces with fine emery paper and
then smear with "super glue".

Hold together tightly for several minutes.

Should be reasonably strong.



..... Phil

 

[David Platt]

In article <isw-F88720.23031910102013@[216.168.3.50]>,
isw <isw@witzend.com> wrote:

Pads don't usually have optimum heat transfer. Metal to metal contact is
optimum, unless surfaces are really off.

That is contrary to everything I've ever known concerning how to couple
a heat sink to a device. Almost without exception, the surfaces are, to
use your term, "really off"; they never make contact at more than a very
few small places.

People who overclock their CPUs or GPUs will often "lap" both the top
of the chip and the bottom of the heatsink, in order to reduce this
surface roughness and improve the metal-to-metal or metal-to-ceramic
contact. The preferred method seems to be something on the order of
"a flat sheet of plate glass, with a sheet of very fine wet-and-dry
abrasive paper taped to it", some water as a lubricant, and some
manual work and care.

From what I've heard, the biggest problem with the use of heat-sink
cream or grease, is that people tend to use much too much of it... too
thick a layer. The method I've seen recommended, is to spread some on
each surface, and then gently scrape or plane most of it off with a
single-edge razor blade, so that you leave only a very thin
film... enough to fill the "low spots" in the surface, but not much
more than that.

Pads (especially the phase-change kind) can avoid the "too thick a
layer" problem to some extent, I imagine, if they're made thin
enough. Some of them are more "solid films" than "pads".

 

[Phil Allison]

"isw"

In fact, because the pads are a lot easier to apply properly than
grease, the pads usually perform a bit better.

** The opposite is true.

1. Pads vary enormously in their performance - the cheapest are silicone
rubber and are shit awful at conducting heat.

2. Nothing beats two smooth, mating metal surfaces with a smear of compound
between.

3. Next best is thin mica insulation (1 or 2 thou of an inch ) with a smear
of compound each side.

Even pressure is crucial to getting good thermal transfer, the usual bolt in
the top part of a TO220 or TO3P metal tab is a horrible way.


.... Phil

 

[David Lesher]

gregz <zekor@comcast.net> writes:

For the record, this is a Mobius camera.
http://www.techmoan.com/blog/2013/7/8/the-mobius-camera-the-do-it-all-mount-anywhere-1080p-micro-c.html

What do you want to do, and why ?

Temporary or permanent ?

The camera has a reputation for running hot. In fairness, the
original market was RC aircraft where forced air cooling is
readily available. Other non-RC users have added heatsinks.



I studied the thermal conductivity issue a few years ago; I was
coupling sensors to copper pipes & comparing approaches. What
I found was any of the pastes & conductive epoxies I found had
thermal resistances so high, vice metal-to-metal, they looked
useful only against air gaps. In other words, they help by not
being air, but lapping is a far better solution.


--
A host is a host from coast to coast.................wb8foz@nrk.com
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433

 

[Arfa Daily]

"Phil Allison" <phil_a@tpg.com.au> wrote in message
news:bbpinfF8louU1@mid.individual.net...

"David Lesher"

I need to add a heatsink to a small product. It has a flat exposed flush
heatsink now; I'm extending with fins.

But the attachment is an issue.


** Suggest you lightly sand the mating surfaces with fine emery paper and
then smear with "super glue".

Hold together tightly for several minutes.

Should be reasonably strong.



.... Phil

I have some heatsink glue. It is made by Permatex and is product code
PX#48020A. It is basically rubber-loaded cyanoacrylate - so 'special'
superglue, really. I do repairs to some professional moving head lights, and
the stepper motor driver ICs have a finned heatsink glued to them. When they
are replaced, it is necessary to attach the heatsink to the new chip, and
this is what I use. Bonds very quickly, is tough to shift once it has
bonded, and seems to conduct the heat into the heatsink well enough. I have
in the past used ordinary superglue as Phil suggests, and it works well
enough, but is a bit more brittle than this rubber loaded stuff

Arfa

 

[dave]

On 10/10/2013 09:35 PM, David Lesher wrote:

I need to add a heatsink to a small product. It has a flat exposed flush
heatsink now; I'm extending with fins.

But the attachment is an issue. Do the pads you put between a CPU & heatsink
provide any stick? Or are the depending on external pressure to compress
them? [I have no way to do that...]

For the record, this is a Mobius camera.
http://www.techmoan.com/blog/2013/7/8/the-mobius-camera-the-do-it-all-mount-anywhere-1080p-micro-c.html

Buy a heatsink made for the CPU. It will have the proper spring. I use
phase change pads with sticky on them, unless I can't match the surface.
I also have the white stuff and mica insulators.