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Message |
k wallace
Guest
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 Posted:
Mon Dec 12, 2005 1:35 am Post subject:
Re: Proper group for heatsink question? |
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| Quote: |
Oh. Homework. Should've said so. Try sci.electronics.design.
Good luck
Chris
They've given a fairly large grant for this to be considered 'homework'. |
The fact that I work at a university rather than in industry does not
automatically imply homework. I am simply the ME on the team. I don't
know as much about some of this as the 3 EE's on the team, regarding the
electronics. My work is in thermal-fluid sciences, so that's what
they've got me for.
I know more specifics on this device, but am constrained from discussing
some of them. Therefore, any vagueness or confusion due to such is
completely my fault.
Thought I could get some general suggestions here for a thermal compound
that needs to function in an enclosed space of prev. posted size at a
T_amb, enclosure of 60C, T_amb, external of 20 C, T_j of 100C, etc. -
that's all I was looking for. I did get a few good suggestions, but on
the whole, it appears that this was not the right group to query. Will
take your (generic) advice, shut up, and go elsewhere.
regards
kw
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John Fields
Guest
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| Posted:
Mon Dec 12, 2005 1:35 am Post subject:
Re: Proper group for heatsink question? |
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On Sun, 11 Dec 2005 14:15:16 -0800, k wallace
<wallace.k@engr.orst.edNOSPAMu> wrote:
| Quote: |
Oh. Homework. Should've said so. Try sci.electronics.design.
Good luck
Chris
They've given a fairly large grant for this to be considered 'homework'.
The fact that I work at a university rather than in industry does not
automatically imply homework. I am simply the ME on the team. I don't
know as much about some of this as the 3 EE's on the team, regarding the
electronics. My work is in thermal-fluid sciences, so that's what
they've got me for.
I know more specifics on this device, but am constrained from discussing
some of them. Therefore, any vagueness or confusion due to such is
completely my fault.
Thought I could get some general suggestions here for a thermal compound
that needs to function in an enclosed space of prev. posted size at a
T_amb, enclosure of 60C, T_amb, external of 20 C, T_j of 100C, etc. -
that's all I was looking for. I did get a few good suggestions, but on
the whole, it appears that this was not the right group to query. Will
take your (generic) advice, shut up, and go elsewhere.
|
---
Check out GC Waldom at:
http://www.gcwaldom.com/catalog.html
Click on 'search' and enter "Catalog 145" to get to their heat sink
compounds.
They've also got spec's in there somewhere, but their site is a
nightmare to navigate, so good luck... :-)
--
John Fields
Professional Circuit Designer |
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John Fields
Guest
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| Posted:
Mon Dec 12, 2005 7:41 am Post subject:
Re: Proper group for heatsink question? |
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On Mon, 12 Dec 2005 00:48:51 +0000, Pooh Bear
<rabbitsfriendsandrelations@hotmail.com> wrote:
| Quote: |
k wallace wrote:
Oh. Homework. Should've said so. Try sci.electronics.design.
Good luck
Chris
They've given a fairly large grant for this to be considered 'homework'.
The fact that I work at a university rather than in industry does not
automatically imply homework. I am simply the ME on the team. I don't
know as much about some of this as the 3 EE's on the team, regarding the
electronics. My work is in thermal-fluid sciences, so that's what
they've got me for.
I know more specifics on this device, but am constrained from discussing
some of them. Therefore, any vagueness or confusion due to such is
completely my fault.
Thought I could get some general suggestions here for a thermal compound
that needs to function in an enclosed space of prev.
That was the *space* and it's enclosed ?
You don't have a hope in hell of dissipating 5W with a delta T of a few 10s
of degrees in that space.
posted size at a
T_amb, enclosure of 60C, T_amb, external of 20 C, T_j of 100C, etc. -
that's all I was looking for. I did get a few good suggestions, but on
the whole, it appears that this was not the right group to query. Will
take your (generic) advice, shut up, and go elsewhere.
You still haven't even mentioned if the 'thermal compound' has to provide
mechanical adhesion ( as in a glued-on heatsink ) or is simply required as
an interface filler where the mechanical aspect is provided by nuts and
bolts or clips..
If you simply *won't* provide any meaningful information *no-one* can help
you.
It's clear to anyone who knows about these things that the minimal info
required is in no way going to create trouble over NDAs or whatever.
You're being deliberately abstruse.
Please don't repeat the same lame question in s.e.d. You'll get a similar
respsonse.
|
---
Not from me, he won't.
All the guy's looking for is some information on what's available in
heat sink compounds and you're ready to tear him a new asshole
because he won't tell you everything you want to know about his
widget?
Get over yourself.
--
John Fields
Professional Circuit Designer
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Pooh Bear
Guest
|
| Posted:
Mon Dec 12, 2005 9:35 am Post subject:
Re: Proper group for heatsink question? |
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Chris wrote:
| Quote: | k wallace wrote:
Oh. Homework. Should've said so. Try sci.electronics.design.
Good luck
Chris
They've given a fairly large grant for this to be considered 'homework'.
The fact that I work at a university rather than in industry does not
automatically imply homework. I am simply the ME on the team. I don't
know as much about some of this as the 3 EE's on the team, regarding the
electronics. My work is in thermal-fluid sciences, so that's what
they've got me for.
I know more specifics on this device, but am constrained from discussing
some of them. Therefore, any vagueness or confusion due to such is
completely my fault.
Thought I could get some general suggestions here for a thermal compound
that needs to function in an enclosed space of prev. posted size at a
T_amb, enclosure of 60C, T_amb, external of 20 C, T_j of 100C, etc. -
that's all I was looking for. I did get a few good suggestions, but on
the whole, it appears that this was not the right group to query. Will
take your (generic) advice, shut up, and go elsewhere.
regards
kw
No good deed goes unpunished -- didn't really say that at all. First,
I gave you quite a bit of _very_ specific advice for a newbie or
hobbyist, which is the assumed audience for s.e.b., and could have been
assumed given your lack of specificity in your original post.
Something vague like your original post is charitably assumed to be the
result of lack of knowledge rather than lack of effort. If you'd spent
more than two minutes on your original post (from further posts, there
obviously was quite a lot more you _could_ have said without bumping up
against non-disclosure), or read the first couple of paragraphs of my
first response, you'd see that and not get offended.
Second, your problem extends a little beyond just heat sink compound (5
watts dissipated by an 0.5" X 0.5" X 4.5" heat sink in free still air
keeping t(j) below 100C and t(sink) below 60C). This seems to be a
very ambitious engineering puzzle, for which there is no easy answer.
Several engineers at s.e.d. have described things they've done with
heat sinks that approach witchcraft, and getting their advice might be
a good idea.
Also, there happened to be some good advice on the heat sink compound
to use in my first post. If you'll look at the website I suggested,
you'd see the Ultrastick phase change product, which has thermal
conductivity ratings better than the others, and looks like it might be
a good starting point (and will probably be cost competitive with the
higher-priced silver-loaded stuff). With something like this, it might
be best to start with the best, then see what kind of margin you have
to play with (unfortunately, I have the suspicion that your margin is
negative already, and getting a really good heat sink compound will
just eliminate that as a source of dither). The manufacturer also will
provide samples, especially if they're talking to someone who is a
potentially good customer.
http://www.aavidthermalloy.com/products/options/greases.shtml
Nobody told you to shut up,
|
To be fair, I indicated that the OP should post more detailed info ( which
certainly needn't have encroached on an NDA ) or 'shut up'.
| Quote: | although I still feel you might get better
advice elsewhere. Sorry you feel that way.
(By the way, look closely at your mathematical modelling, check your
assumptions, and make sure you can actually accomplish what you want
first. I'm not too sure even a perfect heat sink of the size you
specify could do the job you need in non-computer-modelled free still
air.)
Good luck
Chris
|
It seems that you too have come to the same conclusion that the enclosure in
which this IC is to be installed is the limiting factor.
I despair sometimes at the poor level of practical skills in engineering
exhibited today - and especially by 'academics'. A basic understanding of heat
flow would have fixed this.
Something this simple should have been considered at the beginning. Leaving '
thermal manageent ' to the end is begging for failure. And sadly it looks like
failure is the conclusion here.
Graham |
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Chris
Guest
|
| Posted:
Mon Dec 12, 2005 9:35 am Post subject:
Re: Proper group for heatsink question? |
|
|
k wallace wrote:
| Quote: |
Oh. Homework. Should've said so. Try sci.electronics.design.
Good luck
Chris
They've given a fairly large grant for this to be considered 'homework'.
The fact that I work at a university rather than in industry does not
automatically imply homework. I am simply the ME on the team. I don't
know as much about some of this as the 3 EE's on the team, regarding the
electronics. My work is in thermal-fluid sciences, so that's what
they've got me for.
I know more specifics on this device, but am constrained from discussing
some of them. Therefore, any vagueness or confusion due to such is
completely my fault.
Thought I could get some general suggestions here for a thermal compound
that needs to function in an enclosed space of prev. posted size at a
T_amb, enclosure of 60C, T_amb, external of 20 C, T_j of 100C, etc. -
that's all I was looking for. I did get a few good suggestions, but on
the whole, it appears that this was not the right group to query. Will
take your (generic) advice, shut up, and go elsewhere.
regards
kw
|
No good deed goes unpunished -- didn't really say that at all. First,
I gave you quite a bit of _very_ specific advice for a newbie or
hobbyist, which is the assumed audience for s.e.b., and could have been
assumed given your lack of specificity in your original post.
Something vague like your original post is charitably assumed to be the
result of lack of knowledge rather than lack of effort. If you'd spent
more than two minutes on your original post (from further posts, there
obviously was quite a lot more you _could_ have said without bumping up
against non-disclosure), or read the first couple of paragraphs of my
first response, you'd see that and not get offended.
Second, your problem extends a little beyond just heat sink compound (5
watts dissipated by an 0.5" X 0.5" X 4.5" heat sink in free still air
keeping t(j) below 100C and t(sink) below 60C). This seems to be a
very ambitious engineering puzzle, for which there is no easy answer.
Several engineers at s.e.d. have described things they've done with
heat sinks that approach witchcraft, and getting their advice might be
a good idea.
Also, there happened to be some good advice on the heat sink compound
to use in my first post. If you'll look at the website I suggested,
you'd see the Ultrastick phase change product, which has thermal
conductivity ratings better than the others, and looks like it might be
a good starting point (and will probably be cost competitive with the
higher-priced silver-loaded stuff). With something like this, it might
be best to start with the best, then see what kind of margin you have
to play with (unfortunately, I have the suspicion that your margin is
negative already, and getting a really good heat sink compound will
just eliminate that as a source of dither). The manufacturer also will
provide samples, especially if they're talking to someone who is a
potentially good customer.
http://www.aavidthermalloy.com/products/options/greases.shtml
Nobody told you to shut up, although I still feel you might get better
advice elsewhere. Sorry you feel that way.
(By the way, look closely at your mathematical modelling, check your
assumptions, and make sure you can actually accomplish what you want
first. I'm not too sure even a perfect heat sink of the size you
specify could do the job you need in non-computer-modelled free still
air.)
Good luck
Chris |
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Pooh Bear
Guest
|
| Posted:
Mon Dec 12, 2005 9:35 am Post subject:
Re: Proper group for heatsink question? |
|
|
John Fields wrote:
| Quote: | On Mon, 12 Dec 2005 00:48:51 +0000, Pooh Bear
rabbitsfriendsandrelations@hotmail.com> wrote:
k wallace wrote:
Oh. Homework. Should've said so. Try sci.electronics.design.
Good luck
Chris
They've given a fairly large grant for this to be considered 'homework'.
The fact that I work at a university rather than in industry does not
automatically imply homework. I am simply the ME on the team. I don't
know as much about some of this as the 3 EE's on the team, regarding the
electronics. My work is in thermal-fluid sciences, so that's what
they've got me for.
I know more specifics on this device, but am constrained from discussing
some of them. Therefore, any vagueness or confusion due to such is
completely my fault.
Thought I could get some general suggestions here for a thermal compound
that needs to function in an enclosed space of prev.
That was the *space* and it's enclosed ?
You don't have a hope in hell of dissipating 5W with a delta T of a few 10s
of degrees in that space.
posted size at a
T_amb, enclosure of 60C, T_amb, external of 20 C, T_j of 100C, etc. -
that's all I was looking for. I did get a few good suggestions, but on
the whole, it appears that this was not the right group to query. Will
take your (generic) advice, shut up, and go elsewhere.
You still haven't even mentioned if the 'thermal compound' has to provide
mechanical adhesion ( as in a glued-on heatsink ) or is simply required as
an interface filler where the mechanical aspect is provided by nuts and
bolts or clips..
If you simply *won't* provide any meaningful information *no-one* can help
you.
It's clear to anyone who knows about these things that the minimal info
required is in no way going to create trouble over NDAs or whatever.
You're being deliberately abstruse.
Please don't repeat the same lame question in s.e.d. You'll get a similar
respsonse.
---
Not from me, he won't.
All the guy's looking for is some information on what's available in
heat sink compounds and you're ready to tear him a new asshole
because he won't tell you everything you want to know about his
widget?
Get over yourself.
|
Hey, John......
I realise I came over as being frustrated at the OP's lack of detail.
I have my reasons though.
The initial post suggested that it was just an interest in a thermal transfer
compound but I dunno, I smelt something.... In any event it wasn't clear if it
was a grease or an epoxy that was required ( hinted at ) and I don't like to
give bad advice.
Read the follow-up posts carefully and the horrible truth finally comes out. The
transfer compound is the last of their problems and likely only was though about
on account of anecdotal comment ( e.g CPU coolers ) . The following data I kind
of extracted as best I could from the follow-up posts.
The OP's data aquisition module is 13m x 13mm x 114? mm
It contains an IC that's ~ 1cm^2 dissipating *5* Watts !
The IC is inside the module which is unventilated.
( There is simply no hope ever of cooling this IC as required )
In fact the determining characteristic thermally is the enclosure dimension
since it's actually *the enclosure* that will need to dissipate the heat.
This explains the posted 'package' temp of 60C. The OP didn't understand that I
was originally referring to the unspecified *IC package* and gave the data probe
package dimensions instead it seems...
The reason for 60C is that IEC regs only allow a delta T of 40C for accessible
parts and if the ambient temp is 20C then the temp of the probe package must not
exceed 60C.
In short it was like trying to get blood out of a stone to ge this far.
The OP's DAQ seems destined for the big trash can in the sky since I know of no
way ( I'm sure there is no way ) to get 5W out of such a small pacakge with a
delta T of 40C.
Typical idiot academics. The first thing they should have considered was the
thermal constraint.
I'll bet that IC has been designed around some power-hungry PLD or similar.
They'll need to consider a new technology. In short, instead of ending, their
project has merely begun.
Graham |
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Bob Masta
Guest
|
| Posted:
Mon Dec 12, 2005 5:35 pm Post subject:
Re: Proper group for heatsink question? |
|
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On Sat, 10 Dec 2005 19:46:52 -0800, k wallace
<wallace.k@engr.orst.edNOSPAMu> wrote:
| Quote: | I have a design project that is nearing the build and test phase. I
need some info re. thermal compounds for attaching a heatsink to an IC,
and I'm wondering if this is a good NG to request that info on, or if
someone would like to direct me to a more appropriate venue.
thanks all,
karinne
|
Just a note of caution: You may run across BeO (beryllium
oxide) touted as a good heat sink material. No doubt, but
be aware that the stuff is incredibly toxic if you get it into a
cut, breathe dust, etc. The manufactured ceramic pieces are
probably not a serious danger (compared to the raw metal or
powdered oxide), but not something to mess around with
as a prototype. No filing, grinding, etc, and handle it with
care. Personally, I'd avoid it if at all possible.
Best regards,
Bob Masta
dqatechATdaqartaDOTcom
D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Home of DaqGen, the FREEWARE signal generator |
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Tim Williams
Guest
|
| Posted:
Mon Dec 12, 2005 5:35 pm Post subject:
Re: Heatsink insulators |
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|
"Bob Masta" <NoSpam@daqarta.com> wrote in message
news:439d81d6.3733134@news.itd.umich.edu...
| Quote: | On Sat, 10 Dec 2005 19:46:52 -0800, k wallace
wallace.k@engr.orst.edNOSPAMu> wrote:
I have a design project that is nearing the build and test phase. I
need some info re. thermal compounds for attaching a heatsink to an IC,
Just a note of caution: You may run across BeO (beryllium
oxide) touted as a good heat sink material.
|
On a related question, what's your opinion of thermal paste vs. silicone
pads vs. mica vs. aluminum nitride or any other conductive ceramic, with or
without paste?
I'm interested in putting a half bridge of 600Vceo IGBTs on the same
heatsink (which will be copper, if I can cast and machine a slab suitably
:).
Tim
--
Deep Fryer: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms |
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