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September 2004

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Subject:
From:
"Paulus, Jim" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Paulus, Jim
Date:
Thu, 30 Sep 2004 12:59:17 -0500
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text/plain
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text/plain (79 lines)
Werner/Mike:
I like Nelco's approach to reporting CTE.  Especially for Z-axis, where the concern is generally what happens over excursions into soldering temps.  Almost everyone's (laminators) data below the Tg on almost all thermoset resin systems is pretty much the same, assuming RC% is equal.  It's what the expansion is above the Tg, along with when (at what temp) that the higher rate takes place.

So then, the primary concern should be the total expansion of the board's thickness when taken from room temp to soldering temp.
And with the % approach, you can compare different materials.  The higher the Tg, the greater the delay before high TE rate kicks in, and the total expansion is less.
For example:
Difunctional FR4:  4.3%
Tetrafunctional FR4: 4.1%
Multifunctional Fr4 (170C): 3.8%
BT:  3.5%
CE:  1.7%
Polyimide:  1.4%

I think the above are pretty close -- did it from memory.

If you're interested in what occurs in thermal cycling (to 125 or 150C), then the action is pretty much below the Tg, and material TE differentiation is due to resin/glass ratio, degree of cure, etc.
Jim Paulus

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Mcmaster, Michael
Sent: Thursday, September 30, 2004 11:47 AM
To: [log in to unmask]
Subject: Re: [TN] 2nd Nelco4000-13

Werner - I know what you mean about the CTE.  They've lumped the CTE above
and below the Tg into one parameter.  I think all material suppliers should
be required to supply CTE from 25C to the material Tg and from the Tg up to
260 or 288C.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Werner Engelmaier
Sent: Thursday, September 30, 2004 9:15 AM
To: [log in to unmask]
Subject: [TN] 2nd Nelco4000-13

 Hi 'Netters,

NELCO4000-13 dat sheet gives no modulus. Also it gives "Z Axis Expansion 
[50°C to 260°C] = 3.5%"--does this mean CTE (z) = 167 ppm/°C? [Sure is a
strange 
way to give a CTE]

Regards,
Werner Engelmaier

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