J
John Larkin
Guest
Does anybody like something better? Like some thermally conductive,
repairable, self-curing stuff?
repairable, self-curing stuff?
J
Joe Gwinn
Guest
On Tue, 21 Mar 2023 10:26:19 -0700, John Larkin
<jlarkin@highlandSNIPMEtechnology.com> wrote:
Cured silicone rubber has a similar thermal impedance, if memory
serves.
There are thermal interface pads made of mineral-loaded urethane or
silicon rubber as well.
..<https://www.henkel-adhesives.com/us/en/products/thermal-management-materials/thermal-gap-pad-materials.html>
Joe Gwinn
<jlarkin@highlandSNIPMEtechnology.com> wrote:
Cured silicone rubber has a similar thermal impedance, if memory
serves.
There are thermal interface pads made of mineral-loaded urethane or
silicon rubber as well.
..<https://www.henkel-adhesives.com/us/en/products/thermal-management-materials/thermal-gap-pad-materials.html>
Joe Gwinn
S
Steve Goldstein
Guest
On Tue, 21 Mar 2023 14:10:01 -0400, Joe Gwinn <joegwinn@comcast.net>
wrote:
There used to be a product called Bergpads or something like that.
wrote:
There used to be a product called Bergpads or something like that.
P
Phil Hobbs
Guest
On 2023-03-22 07:23, Steve Goldstein wrote:
Thermal gap pads have come a really long way since the original
fiberglass Silpads. Nowadays they come in both elastomeric (rubbery)
and clay-like consistencies, with thermal conductivities up to nearly 10
W/m/K, versus 0.85 for white thermal paste and something horrible like
0.5 for the old-timey Silpads. We have a couple of products that rely
heavily on that.
One is a laser / TEC controller, smaller than a credit card, with a
two-sided load and a fair number of 2-3 mm tall inductors and
capacitors. There isn\'t a lot of space for thermal pours, so we use
small ones and embed one side of the board in a 3.5-mm thick gap pad to
get the heat out.
We use the clay-like ones for that, because it more or less eliminates
the bending stress on the board, which might lead to reliability
problems otherwise. The material is also slightly rubbery, so that
plastic flow doesn\'t entirely eliminate the compressive preload,
preventing delamination under temperature cycling. (They\'re just about
perfect for the job, which I never thought I\'d say about any thermal
interface material.)
The other is a SiPM front end with bias regulation and TEC control.
It\'s even smaller, but the real parlor trick is that it has to work in
high vacuum, inside a SEM chamber. (It\'s used for cathodoluminescence
detection--cool gizmo.) Thus it has to have very low outgassing, which
this one does. (It\'s one of the elastomeric kind.)
(JL uses gap pads too.)
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510
http://electrooptical.net
http://hobbs-eo.com
Thermal gap pads have come a really long way since the original
fiberglass Silpads. Nowadays they come in both elastomeric (rubbery)
and clay-like consistencies, with thermal conductivities up to nearly 10
W/m/K, versus 0.85 for white thermal paste and something horrible like
0.5 for the old-timey Silpads. We have a couple of products that rely
heavily on that.
One is a laser / TEC controller, smaller than a credit card, with a
two-sided load and a fair number of 2-3 mm tall inductors and
capacitors. There isn\'t a lot of space for thermal pours, so we use
small ones and embed one side of the board in a 3.5-mm thick gap pad to
get the heat out.
We use the clay-like ones for that, because it more or less eliminates
the bending stress on the board, which might lead to reliability
problems otherwise. The material is also slightly rubbery, so that
plastic flow doesn\'t entirely eliminate the compressive preload,
preventing delamination under temperature cycling. (They\'re just about
perfect for the job, which I never thought I\'d say about any thermal
interface material.)
The other is a SiPM front end with bias regulation and TEC control.
It\'s even smaller, but the real parlor trick is that it has to work in
high vacuum, inside a SEM chamber. (It\'s used for cathodoluminescence
detection--cool gizmo.) Thus it has to have very low outgassing, which
this one does. (It\'s one of the elastomeric kind.)
(JL uses gap pads too.)
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510
http://electrooptical.net
http://hobbs-eo.com
J
John Larkin
Guest
On Wed, 22 Mar 2023 08:14:50 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
The problem with gap-pads and the phase-change things is that they
don\'t squash thin, and don\'t conduct heat very well, so have a lot of
net theta. Silicone grease squashes down to micro-inches, basically
metal-to-metal for flat surfaces.
Some people don\'t want any silicone grease in their clean rooms.
I was thinking about something that flows like grease but eventually
sets so is not messy. 2-part or heat cure. I was just wondering if
anyone has used stuff like this.
I can get six TO-220 mosfets on a copper CPU cooler, with a custom AlN
insulator. I want max power dissipation. It\'s a tricky packaging
puzzle.
TO-220 0.24 in^2 2 w/m-K 5 mils thick >> 0.4 K/W
times 50 watts is 20 K.
<pcdhSpamMeSenseless@electrooptical.net> wrote:
The problem with gap-pads and the phase-change things is that they
don\'t squash thin, and don\'t conduct heat very well, so have a lot of
net theta. Silicone grease squashes down to micro-inches, basically
metal-to-metal for flat surfaces.
Some people don\'t want any silicone grease in their clean rooms.
I was thinking about something that flows like grease but eventually
sets so is not messy. 2-part or heat cure. I was just wondering if
anyone has used stuff like this.
I can get six TO-220 mosfets on a copper CPU cooler, with a custom AlN
insulator. I want max power dissipation. It\'s a tricky packaging
puzzle.
TO-220 0.24 in^2 2 w/m-K 5 mils thick >> 0.4 K/W
times 50 watts is 20 K.
W
whit3rd
Guest
On Tuesday, March 21, 2023 at 10:26:30â¯AM UTC-7, John Larkin wrote:
To spread heat through conduction, there\'s springy clips, waxy pads,
rubbery pads, glues, solder, greasy compounds, and fluorinert.
Every vendor claims theirs is \'something better\'.
Every one of those solutions is \'something better\' than the old mica insulator
and grease of yesteryear. In mass production, I\'d imagine the micropipet
and glue option is attractive. Is that wrong?
To spread heat through conduction, there\'s springy clips, waxy pads,
rubbery pads, glues, solder, greasy compounds, and fluorinert.
Every vendor claims theirs is \'something better\'.
Every one of those solutions is \'something better\' than the old mica insulator
and grease of yesteryear. In mass production, I\'d imagine the micropipet
and glue option is attractive. Is that wrong?
J
Joe Gwinn
Guest
On Wed, 22 Mar 2023 08:57:13 -0700, John Larkin
<jlarkin@highlandSNIPMEtechnology.com> wrote:
And with good reason.
I think that there are alumna-loaded urethane rubber materials that
set when catalyzed, which might work.
Master Bond and Henkel would be places to start.
Those AiN chicklets are very good. Some people attach them with
silver-loaded epoxy, being careful not to make an electrical bridge in
the process.
Joe Gwinn
<jlarkin@highlandSNIPMEtechnology.com> wrote:
And with good reason.
I think that there are alumna-loaded urethane rubber materials that
set when catalyzed, which might work.
Master Bond and Henkel would be places to start.
Those AiN chicklets are very good. Some people attach them with
silver-loaded epoxy, being careful not to make an electrical bridge in
the process.
Joe Gwinn
P
Phil Hobbs
Guest
On 2023-03-22 11:57, John Larkin wrote:
Go figure.
But remains removable, I gather? Because there\'s really good silver
epoxy available, such as Diemat DM6030HK or Epo-Tek H20E. They\'re used
for die-attach of expensive chips that you don\'t want to braze.
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510
http://electrooptical.net
http://hobbs-eo.com
Go figure.
But remains removable, I gather? Because there\'s really good silver
epoxy available, such as Diemat DM6030HK or Epo-Tek H20E. They\'re used
for die-attach of expensive chips that you don\'t want to braze.
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510
http://electrooptical.net
http://hobbs-eo.com
J
John Larkin
Guest
On Wed, 22 Mar 2023 12:45:31 -0400, Joe Gwinn <joegwinn@comcast.net>
wrote:
I plan to use a single big AlN insulator with six holes, with the six
mosfets bolted down. I have a source that will make custom AlN parts
like this for a couple dollars each.
wrote:
I plan to use a single big AlN insulator with six holes, with the six
mosfets bolted down. I have a source that will make custom AlN parts
like this for a couple dollars each.
J
John Larkin
Guest
On Wed, 22 Mar 2023 09:16:59 -0700 (PDT), whit3rd <whit3rd@gmail.com>
wrote:
Mica adds a lot of thermal resistance. So do pads. I plan to insulate
with AlN, which conducts heat about as well as an aluminum alloy. But
it would still benefit from some gap filler gunk, and silicone grease
is messy.
Thermally conductive epoxy would work but is nasty to rework if a fet
dies.
I guess I\'ll have to contact a bunch of goo suppliers. I was hoping
someone here had suggestions.
wrote:
Mica adds a lot of thermal resistance. So do pads. I plan to insulate
with AlN, which conducts heat about as well as an aluminum alloy. But
it would still benefit from some gap filler gunk, and silicone grease
is messy.
Thermally conductive epoxy would work but is nasty to rework if a fet
dies.
I guess I\'ll have to contact a bunch of goo suppliers. I was hoping
someone here had suggestions.
J
Jim MacArthur
Guest
Loctite 384:
https://www.henkel-adhesives.com/us/en/product/structural-adhesives/loctite_384.html
Not the best thermal specs, but definitely removable. That\'s what they mean when they say \"controlled strength permits field service and repairs\"
I\'ve been having a hard time finding it test days, so let me know if you track down a distributor.
-Jim M.
https://www.henkel-adhesives.com/us/en/product/structural-adhesives/loctite_384.html
Not the best thermal specs, but definitely removable. That\'s what they mean when they say \"controlled strength permits field service and repairs\"
I\'ve been having a hard time finding it test days, so let me know if you track down a distributor.
-Jim M.
J
John Larkin
Guest
On Wed, 22 Mar 2023 13:28:34 -0700 (PDT), Jim MacArthur
<jimbmacarthur@gmail.com> wrote:
Repairable Loctite is an interesting idea. That one has a thermal
conductivity of 0.75 W/mK, but that\'s tolerable if it squashes out
very thin under pressure.
0.0005\" thick, under a TO-220, would be about 0.1 K/W.
<jimbmacarthur@gmail.com> wrote:
Repairable Loctite is an interesting idea. That one has a thermal
conductivity of 0.75 W/mK, but that\'s tolerable if it squashes out
very thin under pressure.
0.0005\" thick, under a TO-220, would be about 0.1 K/W.
P
Phil Hobbs
Guest
On 2023-03-22 17:34, John Larkin wrote:
Gotta watch out for delamination, though--the shear stress goes as the
reciprocal of the bond line thickness.
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510
http://electrooptical.net
http://hobbs-eo.com
Gotta watch out for delamination, though--the shear stress goes as the
reciprocal of the bond line thickness.
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510
http://electrooptical.net
http://hobbs-eo.com
P
Phil Hobbs
Guest
On 2023-03-22 17:51, Phil Hobbs wrote:
Indium foil works pretty well--it\'s super ductile, and you can get
little handheld rolling mills for a couple of hundred bucks, so you can
make the foil any thickness you like, within reason.
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510
http://electrooptical.net
http://hobbs-eo.com
Indium foil works pretty well--it\'s super ductile, and you can get
little handheld rolling mills for a couple of hundred bucks, so you can
make the foil any thickness you like, within reason.
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510
http://electrooptical.net
http://hobbs-eo.com
D
Dan Nygren
Guest
On Tuesday, March 21, 2023 at 10:26:30â¯AM UTC-7, John Larkin wrote:
For our low-outgassing application, we are using Loctite Stycast 2850 Catalyst 24LV .
https://www.henkel-adhesives.com/us/en/product/encapsulants/loctite_stycast_2850ktcat24lv.html
For our low-outgassing application, we are using Loctite Stycast 2850 Catalyst 24LV .
https://www.henkel-adhesives.com/us/en/product/encapsulants/loctite_stycast_2850ktcat24lv.html
J
John Larkin
Guest
On Thu, 23 Mar 2023 09:24:36 -0700 (PDT), Dan Nygren
<dan.nygren@gmail.com> wrote:
2.3 w/mK is good. We could use that to stick the big AlN insulator to
the CPU cooler, which wouldn\'t need to be reworked. That leaves six
TO-220 mosfets to be thermally bonded to the top of the insulator,
which I prefer to be re-workable.
<dan.nygren@gmail.com> wrote:
2.3 w/mK is good. We could use that to stick the big AlN insulator to
the CPU cooler, which wouldn\'t need to be reworked. That leaves six
TO-220 mosfets to be thermally bonded to the top of the insulator,
which I prefer to be re-workable.
N
none
Guest
In article <0uem1ipapfb7gil5cp5rvamhl2d2l871in@4ax.com>,
John Larkin <xx@yy.com> wrote:
would be as good as any kind of gue, glue or whatever.
This works, given that AlN is not conductive.
Groetjes Albert
--
Don\'t praise the day before the evening. One swallow doesn\'t make spring.
You must not say \"hey\" before you have crossed the bridge. Don\'t sell the
hide of the bear until you shot it. Better one bird in the hand than ten in
the air. First gain is a cat spinning. - the Wise from Antrim -
John Larkin <xx@yy.com> wrote:
I would lap the surface to submicron fit. The slightest pressure
would be as good as any kind of gue, glue or whatever.
This works, given that AlN is not conductive.
Groetjes Albert
--
Don\'t praise the day before the evening. One swallow doesn\'t make spring.
You must not say \"hey\" before you have crossed the bridge. Don\'t sell the
hide of the bear until you shot it. Better one bird in the hand than ten in
the air. First gain is a cat spinning. - the Wise from Antrim -
J
John Larkin
Guest
On Mon, 10 Apr 2023 15:43:19 +0200, albert@cherry.(none) (albert)
wrote:
The AlN that we buy is ground mirror flat, and I assume the mosfets
are pretty flat too.
I\'d still prefer some sort of filler, some nongreasy grease. One of
the repairable loctites might be good.
There will be six fets on one big insulator, on a copper cooler. I\'ll
do the fets different ways and thermal image and compare. No goo at
all would sure be nice.
wrote:
The AlN that we buy is ground mirror flat, and I assume the mosfets
are pretty flat too.
I\'d still prefer some sort of filler, some nongreasy grease. One of
the repairable loctites might be good.
There will be six fets on one big insulator, on a copper cooler. I\'ll
do the fets different ways and thermal image and compare. No goo at
all would sure be nice.