if it is standard epoxy filled with silver, my guess is 3x TCE above Tg.
With absent of data and not going to do any test (which I think you
really should do the test... rather than question it endlessly, why not
just pay few $ run a TMA?), I would design per 3x TCE above Tg, provide
you cure it properly. On the other hand, why Dupont not provide above
Tg data? very strange...
my 2 cents.
jk
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Mcmaster, Michael
Sent: Monday, March 24, 2003 5:41 PM
To: [log in to unmask]
Subject: Re: [TN] FW: [TN] TCE above Tg for Dupont CB100 silver resin
I'm going to have to disagree with Guy on this. There's nothing that
says CTE above Tg has to be non-linear. Nor is there anything that says
it has to be linear, especially when working with systems like today's
high performance epoxy systems.
There are multiple ways to define, measure, and determine Tg, but it is
generally regarded as the temperature below which free rotations cease
because of intramolecular energy barriers. In other words, the material
acts as a glass.
Above Tg the polymer achieves what is known as segmental mobility. The
reason for this is that as you heat the material up it expands (the
CTE). This expansion results in an increase in free volume. Below, Tg,
the free volume is too small to allow segmental mobility, whereas above
Tg, the free volume is large enough.
The Tg the shows up as a discontinuity in the specific volume vs
temperature curve. For amorphous polymers, especially something like a
cross-linked epoxy, the transition is not clean. Difference in cross
link density, segment length, initial free volume and other factors mean
that different sections of the material achieve the necessary free
volume for segmental mobility at different temperatures. As a result,
the glass transition is usually not abrupt (like say, the melting of
water, another transition). So while the Tg is reported as a single
temperature, that's rarely true. The temperature is usually arrived at
by extrapolating the specific volume vs temperature curves above and
below Tg. The reported Tg is the intersection of the two lines, even
though the transition itself started below and continued above this
temperature.
For CTE above Tg to be restricted to "non-linear" or "linear" is
unfounded. I've seen plenty of TMA scans that exhibit linear behavior
for at least some section above the Tg. I've also seen materials that
exhibit very non-linear behavior. Much of this has to do with the
highly variable structures and compositions of polymeric materials. You
have materials that are difunctional, tetrafunctional, mulitifunctional
and then the co-polymer blends that tend to exhibit multiple transitions
to the point where you can't find two lines from a TMA scan to
extrapolate to an intersection. In some cases, it's nearly impossible
to get a good Tg determination from TMA alone and alternative methods
such as DSC and DMA must be used. But these look at properties other
than volume to determine the transition and don't necessarily give the
same result.
And I'm guessing that you don't really care whether it's truly linear or
not as along as it's a reasonable approximation of the CTE in the
temperature range of interest. In all likelihood you want to know how
the material is going to perform during reflow soldering (from below to
above Tg). And maybe the properties during the operational life (likely
below Tg). So you need to know the Tg, preferably measured with TMA
since that is how CTE is measured also. You need to know the
temperature range for the CTE measurements. You at least want the value
above and below Tg. Reporting and using a CTE value that is the
combination of the values above and below Tg is not of any practical
value. The material exhibits this particular behavior only at one very
specific temperature during the transition phase. It's akin to a
stopped watch being right twice per day.
Like you, I've had no luck determining the CTE of CB-100 above Tg.
Mike McMaster
RF Product Engineer
Merix Corporation
503-992-4263
----------
From: Arbour, Michel[SMTP:[log in to unmask]]
Reply To: TechNet E-Mail Forum.;Arbour, Michel
Sent: Monday, March 24, 2003 6:10 AM
To: [log in to unmask]
Subject: [TN] FW: [TN] TCE above Tg for Dupont CB100 silver resin
> OK,
> So the values for ZTCE > Tg given in the material specs or various
> articles
> are linear approximation of the behaviour of ZTCE >Tg . Right ??
>
> And the Zaxis expansion% (50 to 288C) is the "real" value ?
>
> Ref. : circuitree magazine Feb. 2001: High reliability/Low CTE epoxy
> technology,
>
>
>
> > -----Original Message-----
> > From: Guy Ramsey [SMTP:[log in to unmask]]
> > Sent: 21 mars, 2003 16:01
> > To: 'TechNet E-Mail Forum.'; 'Arbour, Michel'
> > Subject: RE: [TN] TCE above Tg for Dupont CB100 silver resin
> >
> > TCE above Tg is non-linear. What you're asking for is like asking
for
> > the distortion characteristics of a amp is after clipping.
> >
> > > -----Original Message-----
> > > From: TechNet [mailto:[log in to unmask]] On Behalf Of Arbour, Michel
> > > Sent: Friday, March 21, 2003 2:52 PM
> > > To: [log in to unmask]
> > > Subject: [TN] TCE above Tg for Dupont CB100 silver resin
> > >
> > >
> > > Hello Techies,
> > > By any chance, would you know what is the TCE > Tg
> > > for Dupont CB100 silver resin ??
> > >
> > > Can't get that info from DuPont's Micro-Circuit
> > > Materials group in the U.S. . They have not measured that
> > > characteristic they said...
>
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