Aluminum oxide insulator safety precautions?

Discussion in 'Electronic Basics' started by John, Aug 10, 2007.

  1. John

    John Guest

    I'll be using TO-247 aluminum oxide insulators between some MOSFETs
    and their heat sinks and wanted to get a safety-related reality check.

    I've checked the MSDS for aluminum oxide and it seems that as long as
    I avoid breathing any dust and wash thoroughly after touching the
    insulators, I'm OK.

    But, I want to do some measurements of the MOSFET's case temperature
    and need to grind a hole in the insulator. I have the Dremel and the
    grinding bits to do it, but before I started I wanted to make sure I
    did this carefully enough.

    Will simply doing this outside in a decent breeze, or thoroughly
    venting the dust if inside, be enough? Assuming I have safety glasses
    on, etc.

    One other question...
    Has anyone actually experienced skin irritation to aluminum oxide
    insulators? I can how a powder could do that but was wondering just
    how nasty these insulators were to handle. :)

    Thanks!
     
    John, Aug 10, 2007
    #1
    1. Advertising

  2. John

    John Larkin Guest

    On Fri, 10 Aug 2007 18:53:31 -0400, John
    <> wrote:

    >I'll be using TO-247 aluminum oxide insulators between some MOSFETs
    >and their heat sinks and wanted to get a safety-related reality check.
    >
    >I've checked the MSDS for aluminum oxide and it seems that as long as
    >I avoid breathing any dust and wash thoroughly after touching the
    >insulators, I'm OK.
    >
    >But, I want to do some measurements of the MOSFET's case temperature
    >and need to grind a hole in the insulator. I have the Dremel and the
    >grinding bits to do it, but before I started I wanted to make sure I
    >did this carefully enough.
    >
    >Will simply doing this outside in a decent breeze, or thoroughly
    >venting the dust if inside, be enough? Assuming I have safety glasses
    >on, etc.
    >
    >One other question...
    >Has anyone actually experienced skin irritation to aluminum oxide
    >insulators? I can how a powder could do that but was wondering just
    >how nasty these insulators were to handle. :)
    >
    >Thanks!


    AlO2 is pretty benign. It's not toxic, so is as dangerous as any other
    dust... sawdust, glass, sand.

    It's not a very good heat conductor. AlN is much better. BeO is even
    better, but BeO is seriously toxic.

    John
     
    John Larkin, Aug 11, 2007
    #2
    1. Advertising

  3. John

    John Guest

    >>>AlO2 is pretty benign. It's not toxic, so is as dangerous as any other
    >>>dust... sawdust, glass, sand.
    >>>
    >>>It's not a very good heat conductor. AlN is much better. BeO is even
    >>>better, but BeO is seriously toxic.


    Thanks John.

    I was considering AlN until I saw that they were about $8 each
    (TO-247, 100pc lots)! I was hoping that AlO2 was good enough to be
    worth the 75-cents they cost. :)

    At $8 each for the AlN, hard-anodizing the heat sink becomes the
    better solution. And you can't beat the thermal impedance of
    anodizing.

    You wouldn't happen to have a source for AlN TO-264 insulators at a
    decent price, would you? TO-247 insulators can work, but the MOSFETs
    are TO-264.

    John
     
    John, Aug 11, 2007
    #3
  4. John

    Rich Grise Guest

    On Fri, 10 Aug 2007 21:20:04 -0400, John wrote:

    >>>>AlO2 is pretty benign. It's not toxic, so is as dangerous as any other
    >>>>dust... sawdust, glass, sand.
    >>>>
    >>>>It's not a very good heat conductor. AlN is much better. BeO is even
    >>>>better, but BeO is seriously toxic.

    >
    > I was considering AlN until I saw that they were about $8 each
    > (TO-247, 100pc lots)! I was hoping that AlO2 was good enough to be
    > worth the 75-cents they cost. :)
    >
    > At $8 each for the AlN, hard-anodizing the heat sink becomes the
    > better solution. And you can't beat the thermal impedance of
    > anodizing.
    >
    > You wouldn't happen to have a source for AlN TO-264 insulators at a
    > decent price, would you? TO-247 insulators can work, but the MOSFETs
    > are TO-264.
    >


    If you have the option to hard anodize, then that's the best bet, as long
    as it can take whatever voltage you're applying. Use good heatsink goo,
    and you should be fine.

    Failing that, what's wrong with mica?

    Good Luck!
    Rich
     
    Rich Grise, Aug 11, 2007
    #4
  5. John

    John Guest

    >>>If you have the option to hard anodize, then that's the best bet, as long
    >>>as it can take whatever voltage you're applying. Use good heatsink goo,
    >>>and you should be fine.
    >>>
    >>>Failing that, what's wrong with mica?
    >>>
    >>>Good Luck!
    >>>Rich


    Max voltage is 55VDC and we're using 1 mil Type III anodizing (0.5mil
    penetration, 0.5mil surface).

    Unfortunately, at the low volumes I'm working with (heat sinks) it's
    pretty expensive to hard anodize. I did six for $30 each, with six
    MOSFETs on each sink. If I can find a decent solution for a lot less
    than $5 a MOSFET (with low thermal impedance as a priority), I'll take
    it!

    I thought mica had a pretty high thermal impedance? I did a quick
    Google check and found a thermal conductivity number of 0.71W/mK.

    Hmmm...using the 15.06W/mK value for the AlO2 insulators I purchased,
    that makes the AlO2 a bit over 21 times more conductive. So, if I can
    find a mica insulator at least 21 times thinner than the 80mil AlO2
    insulators I have, that means that the mica would be a better choice?
    That means the mica must be about 3.5mils or thinner (and still
    insulate to 55V at that thickness).

    John
     
    John, Aug 11, 2007
    #5
  6. John

    John Larkin Guest

    On Fri, 10 Aug 2007 22:19:03 -0400, John
    <> wrote:

    >>>>If you have the option to hard anodize, then that's the best bet, as long
    >>>>as it can take whatever voltage you're applying. Use good heatsink goo,
    >>>>and you should be fine.
    >>>>
    >>>>Failing that, what's wrong with mica?
    >>>>
    >>>>Good Luck!
    >>>>Rich

    >
    >Max voltage is 55VDC and we're using 1 mil Type III anodizing (0.5mil
    >penetration, 0.5mil surface).
    >
    >Unfortunately, at the low volumes I'm working with (heat sinks) it's
    >pretty expensive to hard anodize. I did six for $30 each, with six
    >MOSFETs on each sink. If I can find a decent solution for a lot less
    >than $5 a MOSFET (with low thermal impedance as a priority), I'll take
    >it!
    >
    >I thought mica had a pretty high thermal impedance? I did a quick
    >Google check and found a thermal conductivity number of 0.71W/mK.
    >
    >Hmmm...using the 15.06W/mK value for the AlO2 insulators I purchased,
    >that makes the AlO2 a bit over 21 times more conductive. So, if I can
    >find a mica insulator at least 21 times thinner than the 80mil AlO2
    >insulators I have, that means that the mica would be a better choice?
    >That means the mica must be about 3.5mils or thinner (and still
    >insulate to 55V at that thickness).
    >


    The advantage of mica is that it's usually very thin. 3 mils is
    common, and 80/3 is 27, so the mica wins over the 80 mil alumina. 1
    mil hard anodize would of course be a lot better than either, and
    would easily stand the voltage.

    I did get a quote, and some sammples, on some AlN insulators, and I
    recall numbers closer to $2. I'll see if I still have the info.

    Are the fet drains common? The best insulator is no insulator!

    John
     
    John Larkin, Aug 11, 2007
    #6
  7. John

    John Guest

    >>>The advantage of mica is that it's usually very thin. 3 mils is
    >>>common, and 80/3 is 27, so the mica wins over the 80 mil alumina. 1
    >>>mil hard anodize would of course be a lot better than either, and
    >>>would easily stand the voltage.


    I just found 3mil mica from Keystone, so there's hope! But I remember
    that mica had even worse thermal ratings than Sil-Pads (and equivalent
    insulators) and those pads had wayyyyy too high a resistance for my
    uses.

    Uh-oh, I just realized that if typical mica was about 3mil thick and
    that mica's specs weren't good enough for the power levels I want to
    reach with these MOSFETs (acting as an electronic load) then the AlO2
    I have may have too high a resistance too.

    LOL, even with the cost, hard anodizing is looking better.


    >>>I did get a quote, and some sammples, on some AlN insulators, and I
    >>>recall numbers closer to $2. I'll see if I still have the info.
    >>>
    >>>Are the fet drains common? The best insulator is no insulator!
    >>>
    >>>John


    Alas, each drain has current sense resistor for the "servo loop"
    controlling each MOSFET (as it acts as an electronic load). :-(

    $2 or so is a great price. If you had access to that AlN info, that
    would be great! Thanks.

    John
     
    John, Aug 11, 2007
    #7
  8. John

    John Larkin Guest

    On Fri, 10 Aug 2007 23:24:24 -0400, John
    <> wrote:

    >>>>The advantage of mica is that it's usually very thin. 3 mils is
    >>>>common, and 80/3 is 27, so the mica wins over the 80 mil alumina. 1
    >>>>mil hard anodize would of course be a lot better than either, and
    >>>>would easily stand the voltage.

    >
    >I just found 3mil mica from Keystone, so there's hope! But I remember
    >that mica had even worse thermal ratings than Sil-Pads (and equivalent
    >insulators) and those pads had wayyyyy too high a resistance for my
    >uses.


    Sil-pads are garbage. Even with huge mounting pressure, they never
    meet the specified thermal conductivity. And they're thick, so thermal
    resistance is high.

    >
    >Uh-oh, I just realized that if typical mica was about 3mil thick and
    >that mica's specs weren't good enough for the power levels I want to
    >reach with these MOSFETs (acting as an electronic load) then the AlO2
    >I have may have too high a resistance too.
    >
    >LOL, even with the cost, hard anodizing is looking better.
    >
    >
    >>>>I did get a quote, and some sammples, on some AlN insulators, and I
    >>>>recall numbers closer to $2. I'll see if I still have the info.
    >>>>
    >>>>Are the fet drains common? The best insulator is no insulator!
    >>>>
    >>>>John

    >
    >Alas, each drain has current sense resistor for the "servo loop"
    >controlling each MOSFET (as it acts as an electronic load). :-(


    Move the resistor to the source!

    John
     
    John Larkin, Aug 11, 2007
    #8
  9. John

    John Guest

    >>>>Alas, each drain has current sense resistor for the "servo loop"
    >>>>controlling each MOSFET (as it acts as an electronic load). :-(
    >>>
    >>>Move the resistor to the source!
    >>>
    >>>John


    Hmm...good idea. I could do that (dealing with some high common mode
    voltages, manageable though) but I'd still need to electrically
    insulate the heat sink and prevent any touching. An enclosure can
    solve that problem but there's a LOT of heat to remove, cost of
    enclosure, etc.

    LOL, there's never an easy way!

    I think I'm seeing why hardcoat anodizing is used. It's keeps me from
    dealing with pads and grease, speeds up assembly, already provides the
    insulation and it looks good. Probably worth calling around for
    better prices.

    I'll still test out those AlO2 pads I have and perhaps some AlN pads
    too (if you find that info for the ~$2 pads). Gotta' get me some
    learnin' about those things and their effect, even if the anodizing
    looks like the best solution

    <deep sigh> I did try Dremeling out a hole for a thermocouple in one
    AlO2 pad earlier today. Hah! I thought that 2 of my grinder/cutter
    bits were carbide but all they did was leave a steel-color smear on
    the surface of the pad. Time to go shopping for something a little
    harder. :)

    John
     
    John, Aug 11, 2007
    #9
  10. John

    Bob Masta Guest

    On Fri, 10 Aug 2007 17:49:26 -0700, John Larkin
    <> wrote:

    >On Fri, 10 Aug 2007 18:53:31 -0400, John
    ><> wrote:
    >
    >>I'll be using TO-247 aluminum oxide insulators between some MOSFETs
    >>and their heat sinks and wanted to get a safety-related reality check.
    >>
    >>I've checked the MSDS for aluminum oxide and it seems that as long as
    >>I avoid breathing any dust and wash thoroughly after touching the
    >>insulators, I'm OK.
    >>
    >>But, I want to do some measurements of the MOSFET's case temperature
    >>and need to grind a hole in the insulator. I have the Dremel and the
    >>grinding bits to do it, but before I started I wanted to make sure I
    >>did this carefully enough.
    >>
    >>Will simply doing this outside in a decent breeze, or thoroughly
    >>venting the dust if inside, be enough? Assuming I have safety glasses
    >>on, etc.
    >>
    >>One other question...
    >>Has anyone actually experienced skin irritation to aluminum oxide
    >>insulators? I can how a powder could do that but was wondering just
    >>how nasty these insulators were to handle. :)
    >>
    >>Thanks!

    >
    >AlO2 is pretty benign. It's not toxic, so is as dangerous as any other
    >dust... sawdust, glass, sand.


    There are big differences in safety when these things are respirable
    dusts. Sawdust, and probably alumina (aluminum oxide or corundum)
    are typically in the "nuisance dust" category, although alumina at
    high concentrations and/or long exposures is known to cause scarring
    leading to Shaver's disease. Silica (silicon dioxide), however, is a
    major component of sand and glass and is a much more serious problem.
    When the particles are fine they cause permanent scarring, enough of
    which leads to slicosis. Those who work with mineral dusts wear
    respirators rated to remove this stuff. (NOT the silly little
    "nuisance dust" masks sold to painters and woodworkers.)

    >It's not a very good heat conductor. AlN is much better. BeO is even
    >better, but BeO is seriously toxic.


    Yeah , BeO is scary stuff! For airborne dust, it's 50 times more
    toxic than Arsenic. Before I got into pottery and started
    reading up on all this toxicity info, I acquired some TO3 BeO pads.
    Now I think I'll just let them sit in their little plastic bags in
    their little plastic parts drawer.... <g>

    Best regards,


    Bob Masta

    D A Q A R T A
    Data AcQuisition And Real-Time Analysis
    www.daqarta.com
    Scope, Spectrum, Spectrogram, Signal Generator
    Science with your sound card!
     
    Bob Masta, Aug 11, 2007
    #10
  11. John

    John Larkin Guest

    On Sat, 11 Aug 2007 05:10:55 -0400, John
    <> wrote:

    >>>>>Alas, each drain has current sense resistor for the "servo loop"
    >>>>>controlling each MOSFET (as it acts as an electronic load). :-(
    >>>>
    >>>>Move the resistor to the source!
    >>>>
    >>>>John

    >
    >Hmm...good idea. I could do that (dealing with some high common mode
    >voltages, manageable though) but I'd still need to electrically
    >insulate the heat sink and prevent any touching. An enclosure can
    >solve that problem but there's a LOT of heat to remove, cost of
    >enclosure, etc.
    >
    >LOL, there's never an easy way!
    >
    >I think I'm seeing why hardcoat anodizing is used. It's keeps me from
    >dealing with pads and grease, speeds up assembly, already provides the
    >insulation and it looks good. Probably worth calling around for
    >better prices.


    We do hard anodize and as I recall it's not real expensive. It's
    probably worth it when you consider how many fets and associated
    driver/sense circuits you may be able to eliminate. Make sure the
    heatsink is *flat* first... most extrusions are wavy and need to be
    fly-cut flat if you want the lowest theta.

    You could also consider heat spreaders: a small, chunky aluminum or
    even copper plate between each fet and the heatsink. The fet is in
    direct contact with the spreader, and the spreader is insulated from
    the sink. The bigger insulator footprint reduces theta.


    >
    >I'll still test out those AlO2 pads I have and perhaps some AlN pads
    >too (if you find that info for the ~$2 pads). Gotta' get me some
    >learnin' about those things and their effect, even if the anodizing
    >looks like the best solution
    >
    ><deep sigh> I did try Dremeling out a hole for a thermocouple in one
    >AlO2 pad earlier today. Hah! I thought that 2 of my grinder/cutter
    >bits were carbide but all they did was leave a steel-color smear on
    >the surface of the pad. Time to go shopping for something a little
    >harder. :)


    What is really cool to measure is true junction temperature. To do
    that, characterize the substrate diode drop vs temp at some small
    current, 10 mA maybe. Then arrange to power up the fet and then
    suddenly, not too many microseconds, disconnect the regular stuff and
    reverse bias 10 mA, and measure the substrate diode again. You can
    even plot the cooloff curve and estimate various thermal time
    constants.

    John
     
    John Larkin, Aug 11, 2007
    #11
  12. John

    John Larkin Guest

    On Sat, 11 Aug 2007 12:40:17 GMT, (Bob Masta)
    wrote:



    >>It's not a very good heat conductor. AlN is much better. BeO is even
    >>better, but BeO is seriously toxic.

    >
    >Yeah , BeO is scary stuff! For airborne dust, it's 50 times more
    >toxic than Arsenic. Before I got into pottery and started
    >reading up on all this toxicity info, I acquired some TO3 BeO pads.
    >Now I think I'll just let them sit in their little plastic bags in
    >their little plastic parts drawer.... <g>
    >


    Apparently it's fine as long as you don't grind it up or anything. You
    can still buy BeO slabs fabbed to your specified dimensions. I can't
    imagine how they manufacture and slice up the stuff, at least how they
    would do that in the USA.

    John
     
    John Larkin, Aug 11, 2007
    #12
  13. John

    John Guest

    >>>We do hard anodize and as I recall it's not real expensive. It's
    >>>probably worth it when you consider how many fets and associated
    >>>driver/sense circuits you may be able to eliminate. Make sure the
    >>>heatsink is *flat* first... most extrusions are wavy and need to be
    >>>fly-cut flat if you want the lowest theta.
    >>>
    >>>You could also consider heat spreaders: a small, chunky aluminum or
    >>>even copper plate between each fet and the heatsink. The fet is in
    >>>direct contact with the spreader, and the spreader is insulated from
    >>>the sink. The bigger insulator footprint reduces theta.


    Good tip on the heat sink flatness. The mounting surface is milled to
    a Rmax of 6.3 (I'm assuming mils). Not a mirror finish but it's not
    bad. I couldn't find any other info on how much my theta-case-to-sink
    could be lowered with a smoother surface.

    I was wondering earlier about using a spreader (100mms square) or
    individual spreaders.

    I'm using six TO-264 FETs on a 100mm square sink mounting surface with
    less than .5" between each FET and between each FET and the edge of
    the sink. A bit over 34% total coverage. Do you think that a
    spreader (or spreaders) could lower the total theta-case-to-sink
    enough to be worth the theta-case-to-sink penalty from the extra
    greased surface (of the spreader)?

    >>>What is really cool to measure is true junction temperature. To do
    >>>that, characterize the substrate diode drop vs temp at some small
    >>>current, 10 mA maybe. Then arrange to power up the fet and then
    >>>suddenly, not too many microseconds, disconnect the regular stuff and
    >>>reverse bias 10 mA, and measure the substrate diode again. You can
    >>>even plot the cooloff curve and estimate various thermal time
    >>>constants.


    Whoa, that's a great idea! :)

    OK, so I'd measure the body diode voltage drop at a low current level
    at several different temperatures representative of where the MOSFET
    would be operating (probably by having another MOSFET on the sink
    running as a load and waiting several minutes for thermal stability
    for each step).

    I could set up a LM317 for the constant-current 10mA supply. I'd then
    use two MOSFETs to switch the main current in/out and the LM317 supply
    out/in. A little bit of care in the timing to not blow anything up
    and I think I could do this. And I have a nice shiny new Natl.
    Instruments DAQ module just itching to plot the body diode voltage!

    Thanks again for your help John.
     
    John, Aug 11, 2007
    #13
  14. On Sat, 11 Aug 2007 09:21:06 -0700, John Larkin wrote:

    > On Sat, 11 Aug 2007 12:40:17 GMT, (Bob Masta)
    > wrote:
    >
    >
    >
    >>>It's not a very good heat conductor. AlN is much better. BeO is even
    >>>better, but BeO is seriously toxic.

    >>
    >>Yeah , BeO is scary stuff! For airborne dust, it's 50 times more
    >>toxic than Arsenic. Before I got into pottery and started
    >>reading up on all this toxicity info, I acquired some TO3 BeO pads.
    >>Now I think I'll just let them sit in their little plastic bags in
    >>their little plastic parts drawer.... <g>
    >>

    >
    > Apparently it's fine as long as you don't grind it up or anything. You
    > can still buy BeO slabs fabbed to your specified dimensions. I can't
    > imagine how they manufacture and slice up the stuff, at least how they
    > would do that in the USA.


    It's possible to work safely with any damn thing if you throw enough money
    and paranoia at it. In petroleum refining, heavy hydrocarbons are
    catalytically 'cracked' and lighter ones are polymerized to make gasoline.
    The catalyst for the first process is silica; no problem. The catalyst
    for the second is *hydrofluoric acid*. I like to think that any bean
    counter who suggests cutting back the multilayered percautions around the
    polymerization plant is shown a safety video that gives him nightmares.
     
    Stephen J. Rush, Aug 11, 2007
    #14
  15. John

    redbelly Guest

    On Aug 11, 5:10 am, John <> wrote:

    > <deep sigh> I did try Dremeling out a hole for a thermocouple in one
    > AlO2 pad earlier today. Hah! I thought that 2 of my grinder/cutter
    > bits were carbide but all they did was leave a steel-color smear on
    > the surface of the pad. Time to go shopping for something a little
    > harder. :)
    >
    > John


    Aluminum oxide is an extremely hard material. I remember trying
    something similar back in grad school, and getting that same grayish
    metal deposit on the previously-white ceramic.

    Time to shop is right, for new carbide bits to replace the ones you've
    dulled. If any thing is going to work with the Dremel I think you'll
    need diamond tooling, but even then you may just rub off the diamond
    grit before it cuts a hole through the aluminimum oxide.

    Regards,

    Mark
     
    redbelly, Aug 12, 2007
    #15
  16. John

    John Guest

    >>>Sil-pads are garbage. Even with huge mounting pressure, they never
    >>>meet the specified thermal conductivity. And they're thick, so thermal
    >>>resistance is high.


    I never drilled through the AlO2 pad as the Dremel bits were wayyyy
    too expensive to even consider using, but I got some testing done.

    I couldn't test the case temperature of the FET thru the AlO2 pad but
    I did measure the drain lead temperature (as it exited the case) and
    using that, along with case temp. w/o the pad, derived the approx.
    junction temperature for the FET with the pad and without.

    It appears that the TO-247 Aavid AlO2 insulators I'm using have
    approx. 0.165 degrees-C/W thermal resistance using a good grease. This
    is about what a K-10 Silpad gives me. Not good.

    Double checking my results by using the thermal conductivity of AlO2
    (from Aavid) and that of a K-10 pad verifies the results above.

    AlO2 conductivity = 15.06 W/m-K, 80 mil thickness
    K-10 pad cond. = 1.1 W/m-K, 6mil thickness

    AlO2 pad is 13.3 times thicker than K-10.
    AlO2 pad is 13.69 times more thermally conductive.

    The numbers balance out almost perfectly.

    I would love to try AlN as it's, IIRC, about 15-20 times more
    thermally conductive than AlO2. Gotta' find it for a decent price
    though (<<<$5/pad for TO0264) or hardcoat anodizing wins. I can't
    afford the thermal penalty of the pads so far.

    John
     
    John, Aug 12, 2007
    #16
  17. John

    John Guest

    >>>Time to shop is right, for new carbide bits to replace the ones you've
    >>>dulled. If any thing is going to work with the Dremel I think you'll
    >>>need diamond tooling, but even then you may just rub off the diamond
    >>>grit before it cuts a hole through the aluminimum oxide.


    I think you're right.
    I went shopping for bits and the diamond ones were $15 each! IMHO,
    not worth the risk of just stripping the diamond off before I get
    through the AlO2.

    Using the drain lead temperature of the MOSFET with and w/o the pad in
    place and the case temperature w/o the pad, I think I was able to
    extrapolate the junction temperature for both scenarios pretty
    accurately. Well, at least accurately enough for my purposes. :)

    John
     
    John, Aug 13, 2007
    #17
  18. John

    Rich Grise Guest

    On Sat, 11 Aug 2007 05:10:55 -0400, John wrote:
    >>>>>Alas, each drain has current sense resistor for the "servo loop"
    >>>>>controlling each MOSFET (as it acts as an electronic load). :-(
    >>>>
    >>>>Move the resistor to the source!

    >
    > Hmm...good idea. I could do that (dealing with some high common mode
    > voltages, manageable though) but I'd still need to electrically
    > insulate the heat sink and prevent any touching. An enclosure can
    > solve that problem but there's a LOT of heat to remove, cost of
    > enclosure, etc.
    >
    > LOL, there's never an easy way!
    >
    > I think I'm seeing why hardcoat anodizing is used. It's keeps me from
    > dealing with pads and grease,


    No, No, No! You still need the goo. I prefer the white pasty stuff to
    just plain silicone grease - in fact I like it so much that when I buy
    a new CPU and heatsink, I clean their goo off the heatsink and use my
    white stuff. One number that comes to mind is Dow Corning DC-340, but
    the little tube of the stuff I have has lasted so long that I can't
    read the label any more. )-;

    Good Luck!
    Rich
     
    Rich Grise, Aug 15, 2007
    #18
  19. John

    John Guest

    >>>No, No, No! You still need the goo. I prefer the white pasty stuff to
    >>>just plain silicone grease - in fact I like it so much that when I buy
    >>>a new CPU and heatsink, I clean their goo off the heatsink and use my
    >>>white stuff. One number that comes to mind is Dow Corning DC-340, but
    >>>the little tube of the stuff I have has lasted so long that I can't
    >>>read the label any more. )-;
    >>>
    >>>Good Luck!
    >>>Rich



    Thanks Rich! I should have said "grease AND pads". I was definitely
    going to use grease. :)

    Currently I have Aavid's phase-change UltraStick and Wakefield's
    non-silicone Series 126 grease.

    The UltraStick has slightly better thermal specs but is hard to get
    thin enough to get those specs. The Wakefield grease is that great
    white pasty stuff you mentioned and goes on incredibly thin. A little
    messier than the UltraStick, but it's probably what I'll stick with.

    I'll check out DC-340 too. I only have a small amount of the
    Wakefield grease so another tub of something else won't be a problem.

    Thanks again!
    John
     
    John, Aug 15, 2007
    #19
  20. John

    John Larkin Guest

    On Wed, 15 Aug 2007 04:17:17 -0400, John
    <> wrote:

    >>>>No, No, No! You still need the goo. I prefer the white pasty stuff to
    >>>>just plain silicone grease - in fact I like it so much that when I buy
    >>>>a new CPU and heatsink, I clean their goo off the heatsink and use my
    >>>>white stuff. One number that comes to mind is Dow Corning DC-340, but
    >>>>the little tube of the stuff I have has lasted so long that I can't
    >>>>read the label any more. )-;
    >>>>
    >>>>Good Luck!
    >>>>Rich

    >
    >
    >Thanks Rich! I should have said "grease AND pads". I was definitely
    >going to use grease. :)
    >
    >Currently I have Aavid's phase-change UltraStick and Wakefield's
    >non-silicone Series 126 grease.
    >
    >The UltraStick has slightly better thermal specs but is hard to get
    >thin enough to get those specs. The Wakefield grease is that great
    >white pasty stuff you mentioned and goes on incredibly thin. A little
    >messier than the UltraStick, but it's probably what I'll stick with.
    >
    >I'll check out DC-340 too. I only have a small amount of the
    >Wakefield grease so another tub of something else won't be a problem.
    >
    >Thanks again!
    >John


    I don't trust the phase-change crayon stuff. It's likely to leave air
    pockets, and I'm not sure if it will ever really flow thin. I've
    measured the white Dow grease as squashing down to below 100
    micro-inches under moderate pressure, about my resolution limit.

    The phase-change pads are definitely garbage.

    John
     
    John Larkin, Aug 16, 2007
    #20
    1. Advertising

Want to reply to this thread or ask your own question?

It takes just 2 minutes to sign up (and it's free!). Just click the sign up button to choose a username and then you can ask your own questions on the forum.
Similar Threads
  1. royalmp2001
    Replies:
    8
    Views:
    571
    Michael A. Terrell
    May 14, 2006
  2. Paul Burridge

    DMOS handling precautions

    Paul Burridge, Sep 17, 2004, in forum: Electronic Design
    Replies:
    5
    Views:
    362
    Mook Johnson
    Sep 18, 2004
  3. Replies:
    0
    Views:
    330
  4. Myauk

    Flux Remover (5252) precautions?

    Myauk, Jan 12, 2009, in forum: Electronic Design
    Replies:
    11
    Views:
    675
    K Ludger
    Jan 15, 2009
  5. High voltage safety precautions

    , May 4, 2009, in forum: Electronic Repair
    Replies:
    16
    Views:
    2,433
Loading...

Share This Page