| Author |
Message |
k wallace
Guest
|
 Posted:
Sun Dec 11, 2005 9:35 am Post subject:
Proper group for heatsink question? |
|
|
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
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Chris
Guest
|
| Posted:
Sun Dec 11, 2005 9:35 am Post subject:
Re: Proper group for heatsink question? |
|
|
k wallace 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
|
Hi. This is an appropriate group.
A good newbie starter is GC Electronics P/N 10-8109 Zinc Oxide and
Silicone-based Heat Sink Compound. It's got a silicone and zinc oxide
base, it's a highly visible white, and it's relatively inexpensive.
This will allow you to do a visual inspection as you develop skill in
applying the right amount of compound between the IC and the heat sink.
Make sure both the surface of the IC and the heat sink are absolutely
clean, and that the heat sink is free of burrs, warping, or other
visible imperfections. I like to do an alcohol wipe with a lint-free
cloth before application of heat sink compound to remove any dust or
grit.
Apply a very small dab of the white zinc oxide/silicone heat sink
compound to your very clean finger (or ideally, with a fresh finger cot
over your index finger) . Rub the compound over the mating surface of
the IC, such that you can barely see through the heat sink compound to
the surface. Then evenly place the heat sink on the IC, and evenly
press down with the clip or fastener.
Now that you've done the work, undo it. Carefully remove the clip or
fastener so that the surface of the heat sink doesn't slide around on
the IC. Then pull it straight off. Look at your work. You should see
a kind of fine fish-scaling of the heat sink compound across the entire
surface of the heat sink like lacework, with a tiny amount of the
compound extruded out past the edges of the IC. If you don't see the
fish-scaling, you (probably) put too much compound on the IC. It's
always way too thick the first time. Start over and do it again, first
wiping the IC and the heat sink clean with alcohol and the lint-free
cloth (it's sometimes better to just scoop off most of it with a paper
towel first, then use the alcohol and the lint-free cloth).
Once you do this successfully a couple of times, you'll be able to do
it well consistently in the future. It's like riding a bike -- you
don't forget. Practice with each type of IC and transistor package.
If you use a TO-3 or other heat sink that requires multiple screws, you
should tighten evenly a little at a time on each side, ideally using a
torque indicator to get the screws tightened down evenly. Just
remember that way too much heat sink compound is actually worse than
none. And by the way, make sure to clean off the heat sink compund
carefully -- it's not good for you.
It also might be a good idea, once you're in practice, to use another
type of heat sink compound if your application is high reliability or
you're dealing with a lot of heat. Plain zinc oxide-based heat sink
compounds tend to dry out and lose their effectiveness over time
(years). Others tend to extrude out over time with thousands of
thermal expansion-contraction cycles. Once you're in practice, and if
you need the reliability, there are a number of translucent
silicone-based compounds that have good thermal conductivity if applied
properly, will not dry out over time, and are viscous enough to stay
put. You might want to look at
http://www.aavidthermalloy.com/
for a variety of good products, and some good technical papers and app
notes.
And of course, there's always the elusive search for the perfect heat
sink compound. The last time I was walking along that path, I started
seeing Monster Cables and other audiophile excesses lurking in the
bushes, so I turned back to avoid brain cramp. But I've heard there
are a number of very expensive silver-loaded heat sink compounds that
have somewhat better thermal conductivity than silicone-based, and
measurably better thermal conductivity than plain-Jane zinc
oxide-silicone. For applications right on the bleeding edge (where the
extra 0.2 degree C/W makes all the difference), you just might need
something this good. But usually, you just put in a bigger fan or go
to water cooling instead.
You might get a more specific answer if you describe what you're doing,
and some more about your project requirements.
Chris |
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k wallace
Guest
|
| Posted:
Sun Dec 11, 2005 9:35 am Post subject:
Re: Proper group for heatsink question? |
|
|
Pooh Bear wrote:
| Quote: |
k wallace 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,
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
What's the IC ?
Graham
oops- I thought that said "Whats *AN* IC?" |
We don't know. We are designing a general thermal solution for future
need. We can assume size of about 1 cm^2 to 1.2 cm^2 for the chip itself.
regards,
karinne
|
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|
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k wallace
Guest
|
| Posted:
Sun Dec 11, 2005 9:35 am Post subject:
Re: Proper group for heatsink question? |
|
|
Chris wrote:
| Quote: | k wallace 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,
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
Hi. This is an appropriate group.
A good newbie starter is GC Electronics P/N 10-8109 Zinc Oxide and
Silicone-based Heat Sink Compound. It's got a silicone and zinc oxide
base, it's a highly visible white, and it's relatively inexpensive.
This will allow you to do a visual inspection as you develop skill in
applying the right amount of compound between the IC and the heat sink.
Make sure both the surface of the IC and the heat sink are absolutely
clean, and that the heat sink is free of burrs, warping, or other
visible imperfections. I like to do an alcohol wipe with a lint-free
cloth before application of heat sink compound to remove any dust or
grit.
Apply a very small dab of the white zinc oxide/silicone heat sink
compound to your very clean finger (or ideally, with a fresh finger cot
over your index finger) . Rub the compound over the mating surface of
the IC, such that you can barely see through the heat sink compound to
the surface. Then evenly place the heat sink on the IC, and evenly
press down with the clip or fastener.
Now that you've done the work, undo it. Carefully remove the clip or
fastener so that the surface of the heat sink doesn't slide around on
the IC. Then pull it straight off. Look at your work. You should see
a kind of fine fish-scaling of the heat sink compound across the entire
surface of the heat sink like lacework, with a tiny amount of the
compound extruded out past the edges of the IC. If you don't see the
fish-scaling, you (probably) put too much compound on the IC. It's
always way too thick the first time. Start over and do it again, first
wiping the IC and the heat sink clean with alcohol and the lint-free
cloth (it's sometimes better to just scoop off most of it with a paper
towel first, then use the alcohol and the lint-free cloth).
Once you do this successfully a couple of times, you'll be able to do
it well consistently in the future. It's like riding a bike -- you
don't forget. Practice with each type of IC and transistor package.
If you use a TO-3 or other heat sink that requires multiple screws, you
should tighten evenly a little at a time on each side, ideally using a
torque indicator to get the screws tightened down evenly. Just
remember that way too much heat sink compound is actually worse than
none. And by the way, make sure to clean off the heat sink compund
carefully -- it's not good for you.
It also might be a good idea, once you're in practice, to use another
type of heat sink compound if your application is high reliability or
you're dealing with a lot of heat. Plain zinc oxide-based heat sink
compounds tend to dry out and lose their effectiveness over time
(years). Others tend to extrude out over time with thousands of
thermal expansion-contraction cycles. Once you're in practice, and if
you need the reliability, there are a number of translucent
silicone-based compounds that have good thermal conductivity if applied
properly, will not dry out over time, and are viscous enough to stay
put. You might want to look at
http://www.aavidthermalloy.com/
for a variety of good products, and some good technical papers and app
notes.
And of course, there's always the elusive search for the perfect heat
sink compound. The last time I was walking along that path, I started
seeing Monster Cables and other audiophile excesses lurking in the
bushes, so I turned back to avoid brain cramp. But I've heard there
are a number of very expensive silver-loaded heat sink compounds that
have somewhat better thermal conductivity than silicone-based, and
measurably better thermal conductivity than plain-Jane zinc
oxide-silicone. For applications right on the bleeding edge (where the
extra 0.2 degree C/W makes all the difference), you just might need
something this good. But usually, you just put in a bigger fan or go
to water cooling instead.
You might get a more specific answer if you describe what you're doing,
and some more about your project requirements.
Chris
what else would you like to know? I can't discuss the exact solution |
we've come up with,(NDA stuff) but I can probably specify other things.
For instance, this package is .013*.013*.114 m in size. junction temp no
higher than 100C, case temp no higher than 60C. Need to dissipate 5W.
Therefore, any extra cooling we can squeeze out of any part of this is
essential. Your response is very helpful, and if you don't mind, I will
print it to share with my other ME team member who has less hands on
experience than I do with any electronic stuff, and I don't have a ton-
limited to home PC builds and hobby RC and robotics projects.
can you indicate why "too much is worse than too little"? We need to
minimize contact resistance as much as possible; we have access to a
totally kick-ass machine shop for the prototype of the heatsink. Water
cooling is not an option, unfortunately, nor is thermoelectric cooling,
but we've come up with something that should work; we now need to
prototype and test.
I've done this with home PC's, but nothing more demanding than that; I
need something that performs really well for reasonable cost, that I can
access an amount of to use in testing.
and...aavid is a great site...as is another one I found,
www.coolingzone.com - that has been quite helpful for tech papers and
the like.
regards,
karinne |
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k wallace
Guest
|
| Posted:
Sun Dec 11, 2005 9:35 am Post subject:
Re: Proper group for heatsink question? |
|
|
Pooh Bear wrote:
| Quote: |
k wallace 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,
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
What's the IC ?
Graham
the integrated circuit. I'm working on a contract/extern basis for a |
well-known company that makes oscilloscopes and data probes. They are
planning for the future with this R&D project- currently, their DAQ
devices need to be able to dissipate about a Watt of heat. My assignment
is to design a thermal management system that can dissipate 5W of heat
in a quite small package (no larger than current data probes). I have a
solution and design that will work, I need now to concentrate on test
and build and retest; thermal compound is part of this thermal
management equation and it's probably the part that I know least about,
material-wise. I've done lots of reading...not only does this have to
work but it has to be (reasonably) economical to manufacture. I've so
far optimized the size and type of heatsink, figured out the rest of the
management package, and need now to find a really good thermal compound
that's not horribly expensive.
regards,
karinne |
|
| Back to top |
|
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Pooh Bear
Guest
|
| Posted:
Sun Dec 11, 2005 9:35 am Post subject:
Re: Proper group for heatsink question? |
|
|
k wallace 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
|
What's the IC ?
Graham |
|
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|
|
Figaro
Guest
|
| Posted:
Sun Dec 11, 2005 9:35 am Post subject:
Re: Proper group for heatsink question? |
|
|
"k wallace" <wallace.k@engr.orst.edNOSPAMu> wrote in message
news:VqmdnZzmAua3PAbeRVn-sw@comcast.com...
| 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
this might help:
http://www.heatsink-guide.com/content.php?content=compound.shtml |
|
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|
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Pooh Bear
Guest
|
| Posted:
Sun Dec 11, 2005 4:40 pm Post subject:
Re: Proper group for heatsink question? |
|
|
k wallace wrote:
| Quote: | Pooh Bear wrote:
k wallace 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,
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
What's the IC ?
Graham
oops- I thought that said "Whats *AN* IC?"
We don't know. We are designing a general thermal solution for future
need. We can assume size of about 1 cm^2 to 1.2 cm^2 for the chip itself.
regards,
|
You can ? How so ? What package would that be ?
It sounds like you're seriously in the dark about thermal management to me.
What is it you're actually trying to acheive ?
'General solutions' makes it sound like someone hasn't a clue what they're
doing.
You might care to check out a heatsink manufacturer's range. See Aavid for
example
Graham |
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|
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Pooh Bear
Guest
|
| Posted:
Sun Dec 11, 2005 4:43 pm Post subject:
Re: Proper group for heatsink question? |
|
|
Chris wrote:
| Quote: | k wallace 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,
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
Hi. This is an appropriate group.
A good newbie starter is GC Electronics P/N 10-8109 Zinc Oxide and
Silicone-based Heat Sink Compound.
|
The OP hasn't got an IC that you can screw / bolt to, so the above is
irrelevant.
Most likely they need some thermal epoxy.
Since the OP doesn't even know the package dissipation there's very little
help that can be offered.
Either the Op gives some relevant info or shuts up.
Graham |
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Pooh Bear
Guest
|
| Posted:
Sun Dec 11, 2005 4:47 pm Post subject:
Re: Proper group for heatsink question? |
|
|
k wallace wrote:
| Quote: | For instance, this package is .013*.013*.114 m in size.
|
13mm x 13mm x 114mm ?
What package is that ?
| Quote: | junction temp no
higher than 100C,
|
Unusual spec. Normally it's 125C or 150C. It would help if you told us what
the IC actually is.
| Quote: | case temp no higher than 60C.
|
Irrelevant. The difference between case temp and junction temp is set by the
junction-to-case thermal resistance. The junction temp is the one to target (
case temp is not important ).
| Quote: | Need to dissipate 5W.
|
You'll need to specify the max operating ambient temp too.
Graham |
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| Back to top |
|
|
PeteS
Guest
|
| Posted:
Sun Dec 11, 2005 5:35 pm Post subject:
Re: Proper group for heatsink question? |
|
|
Pooh Bear wrote:
| Quote: | k wallace wrote:
For instance, this package is .013*.013*.114 m in size.
13mm x 13mm x 114mm ?
What package is that ?
junction temp no
higher than 100C,
Unusual spec. Normally it's 125C or 150C. It would help if you told us what
the IC actually is.
|
I worked with an Infiniband switch from Agilent that had an absolute
max junction temp of 110C (but it quit operating properly at 100C
anyway). That was a fair sized device (about 28mm x 28mm square)
flipchip, so junction to case/heatsink thermal resistance was almost 0.
Had a big heatsink on it as it dissipated about 18W, 12 of them inside
a 1U enclsure, so managing even the ambient temp was painful.
Obviously, that system had fans.
| Quote: |
case temp no higher than 60C.
Irrelevant. The difference between case temp and junction temp is set by the
junction-to-case thermal resistance. The junction temp is the one to target (
case temp is not important ).
Need to dissipate 5W.
You'll need to specify the max operating ambient temp too.
Graham
|
I agree that without knowing the device for junction to case thermal
resistance and ambient, the OP will have an impossible time designing
heat management for it.
Cheers
PeteS |
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| Back to top |
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|
Chris
Guest
|
| Posted:
Sun Dec 11, 2005 5:35 pm Post subject:
Re: Proper group for heatsink question? |
|
|
k wallace wrote:
| Quote: | Pooh Bear wrote:
What's the IC ?
Graham
the integrated circuit. I'm working on a contract/extern basis for a
well-known company that makes oscilloscopes and data probes. They are
planning for the future with this R&D project- currently, their DAQ
devices need to be able to dissipate about a Watt of heat. My assignment
is to design a thermal management system that can dissipate 5W of heat
in a quite small package (no larger than current data probes). I have a
solution and design that will work, I need now to concentrate on test
and build and retest; thermal compound is part of this thermal
management equation and it's probably the part that I know least about,
material-wise. I've done lots of reading...not only does this have to
work but it has to be (reasonably) economical to manufacture. I've so
far optimized the size and type of heatsink, figured out the rest of the
management package, and need now to find a really good thermal compound
that's not horribly expensive.
regards,
karinne
|
Oh. Homework. Should've said so. Try sci.electronics.design.
Good luck
Chris |
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Pooh Bear
Guest
|
| Posted:
Mon Dec 12, 2005 1:35 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.
|
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.
| Quote: | 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.
Graham |
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Pooh Bear
Guest
|
| Posted:
Mon Dec 12, 2005 1:35 am Post subject:
Re: Proper group for heatsink question? |
|
|
k wallace wrote:
| Quote: | I've so
far optimized the size and type of heatsink,
|
How can you do that without even knowing the ambient temperature ? Have you
made one and measured its thermal resistance ?
| Quote: | figured out the rest of the
management package,
|
What's this 'management package' ?
| Quote: | and need now to find a really good thermal compound
that's not horribly expensive.
|
You simply want thermal transfer 'grease' ?
Graham |
|
| Back to top |
|
|
John Larkin
Guest
|
| Posted:
Mon Dec 12, 2005 1:35 am Post subject:
Re: Proper group for heatsink question? |
|
|
On Sat, 10 Dec 2005 23:59:17 -0500, "Figaro" <Figaro@mailinator.com>
wrote:
| Quote: |
"k wallace" <wallace.k@engr.orst.edNOSPAMu> wrote in message
news:VqmdnZzmAua3PAbeRVn-sw@comcast.com...
| 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
this might help:
http://www.heatsink-guide.com/content.php?content=compound.shtml
|
From that page:
"Today, there are far more advanced thermal pads available, made by
companies such as Power Devices, Bergquist or Chomerics, to name only
a few. For links to the web sites of these companies, check out the
links page. The performance of these pads can be roughly equal to
standard thermal compound."
That is, in nearly all situations, grossly untrue. The thermal pads,
or the phase-change stuff, wind up being 2-10 mills thick, even if you
manage to apply insane contact pressures. Regular thermal silicone
grease or thermal epoxy will squish down below 100 microinches with
mild pressure, so will have an interface thermal resistance of 1/20 or
more likely 1/100 of the pads. At, maybe, 2% of the cost.
And all the thermal pad vendors lie their asses off on thermal
resistance specs. If you want to blow up power fets, use Bergquist
pads.
John |
|
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|
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