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January 2013

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Subject:
From:
Inge Hernefjord <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Inge Hernefjord <[log in to unmask]>
Date:
Thu, 31 Jan 2013 14:18:05 +0100
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  A propos Heat sink, there are now about 20 reports and articles on Heat
transportation
on my Dropbox. E.g. a 20 pages long slideshow from GORE. Explains how heat
is transfered in the adhesive  matrix and what you should know.
And more will come.

Inge



 On 31 January 2013 00:32, Steven Creswick <[log in to unmask]>wrote:

> Victor,
>
> You definitely need to review the product data sheet and MSDS for the
> specific thermal compound which you are using.
>
> The Product Data sheet should list the dielectric constant, which can give
> you an idea of what impact this material might have on your circuit's
> operation.
>
> The Product data sheet should also list the breakdown voltage of the paste.
> It will likely range from 100's to 1000's of volts/mil, etc.
>
> Hopefully, the MSDS would tell you if you have a metal filler.  Most likely
> it is an oxide filler, but you need to check for sure.
>
> Some thermal materials harden up quite distinctly, others remain 'squishy
> and sticky' for a long time, as I believe it was Larry that mentioned.  If
> your material is one of those that hardens, I would immediately begin to be
> concerned.  One of the first things I would contemplate is doing some DSC
> testing to get a feel for the material's thermal coefficient of expansion
> over the temperature range that is applicable to your product.  Silicones
> will typically have high CTE's [100-200 PPM/°C], but may have a low enough
> modulus to not be offensive to your product.
>
> I've never done it, but you might be able to suction off some of the excess
> paste, if it is a gel/grease-like material.  Regardless, it will still be a
> huge mess.
>
> As has been said, we can't definitively answer your question about
> functionality since we don't know the specific material, nor the circuit,
> nor application.
>
>
> Steve Creswick
> Sr Associate - Balanced Enterprise Solutions
> http://www.linkedin.com/in/stevencreswick
>                          616 834 1883
>
>
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Inge Hernefjord
> Sent: Wednesday, January 30, 2013 4:17 PM
> To: [log in to unmask]
> Subject: Re: [TN] Gray Thermal Heat Sink Compound-paste
>
> Hi Vic Tor,
> Application of thermal paste is an art.The interface between the heat
> generating component and the surrounding is often meticously calculated,
> because the heat transfer capability and precision decides the life of the
> component .either it's chip, a BGA, a power transistorr or else. Removal of
> heat is often the most forgotten parameter. One reason why Ericsson had
> such
> a success decade after decade is that a guy started todig deeply into this
> topic. He made models, travelled around and preached his 2cooling message"
> on Ericsson's facilities and fostered a whole generation of design
> engineers
> to do better heat transferrng constructions.
>
> The heat flow is representated in a equation as a lot of series- and
> parallel coupled resistances, with addition of series/parallel coupled
> capacitors. Now, let' s take a power transistor against a chassis. If you
> torque the package naked, you get three main heat flows:
> convection/radiation to ambient, a flow path creatid by the many
> metal-to-metal contacts and radiation cross the micrometer thick non-metal.
> I performed the calculations for leading away heat om a super computer. The
> volume for the twenty stacked wafers was  a cube, 12 inches sides, and my
> job was to remove  12,000 Watts peak power! I filled the gap between the
> wafers with Helium and the heat exchange was a ,salt solution.
>
> Now Vic Tor, if you fill the space wth 'a good thick layer' you may make a
> big mistake, depending on what paste you use. The heat transfer of a paste
> is not super, which many think. A thick layer can result in a worse heat
> transfer, than a naked , well torqued transistor. The paste is used only
> for
> improving the volumes of non-physical contact, i.e. something that is
> better
> than air. If you have a fat paste or mat layer, you risk that the
> metal-to-metal contacts be fewer. And there is a risk for material flow,
> whereby the the important good contacts become fewer too.With other words :
> use as thin fill-up as possible.
>
> I have some real good stuff  about this, but my contract fromEricsson is
> vivid as long as I live. In my opinion there is nothing that isn't found in
> today's computer models, but Ericsson are extremly stringent. But you'll
> manage on your own, there are lots to buy, put in your facts, press enter
> and the computer does the job.
>
> I will add some good stuff in my Dropbox, will take little time...
>
> Inge
>
>
>
>
> On 30 January 2013 16:22, Victor Hernandez
> <[log in to unmask]>wrote:
>
> > Folks,
> >
> >    Again I state my inquiry, " Can/theatrically excessive saturation
> > of the SMT components-BGA, etc. devices with the above stated product can
> a
> > leakage condition".   I don't feel I got an answer.   I am very aware
> that
> > the placement of the paste should only be over the die surface and with a
> > control volume.    I don't have the brand and/or composition make of the
> > gray material before me, only the aftermath effects of the component
> > /BGA over saturation.
> >
> > Victor,
> >
> > -----Original Message-----
> > From: TechNet [mailto:[log in to unmask]] On Behalf Of Nutting, Phil
> > Sent: Wednesday, January 30, 2013 9:05 AM
> > To: [log in to unmask]
> > Subject: Re: [TN] Gray Thermal Heat Sink Compound-paste
> >
> > Hi guys,
> >
> > In our testing the type of thermal paste does not make a difference if
> > the surfaces are really smooth (16 µin or better surface).  Where it
> > makes a difference is in rougher surfaces.  And Brian is right, more is
> not better.
> >
> > For electrical isolation we have switch from a thixotropic phase
> > change material (Isostrate) to T-gard with great results.
> >
> > Just my 2 ¢
> >
> > Phil
> >
> > -----Original Message-----
> > From: TechNet [mailto:[log in to unmask]] On Behalf Of Brian Ellis
> > Sent: Wednesday, January 30, 2013 9:52 AM
> > To: [log in to unmask]
> > Subject: Re: [TN] Gray Thermal Heat Sink Compound-paste
> >
> > It depends.... on its composition. If it's grey, it may rely on fine
> > metallic powder. I have some Thermaltake TG2 which the makers claim
> > has low electrical conductivity but I suspect it may have metal in it.
> > I use it for CPUs to radiators, so its electrical characteristics are
> unimportant.
> > Consult the manufacturer's data. BTW, don't put on an excess; if it
> > squeezes out, you're wasting a costly product :(
> >
> > Brian
> >
> > On 30/01/2013 15:41, Victor Hernandez wrote:
> > > Folks,
> > >
> > >     Can excessive saturation of the SMT components-BGA, etc. devices
> > with the above stated product can a leakage condition.   Cosmetic wise
>  it
> > doesn't look pretty.   I am concern functionally over a long period of
> time.
> > >
> > > Victor,
> > >
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