Hi Val!

I'm not sure I have ever seen a position on this formally in IPC.

As you know, each method seeks to identify an important material
"transition" based on its' response to the stimulii. You get different
numbers because the stimulii are different.

As you know, I favor and specify TMA which measures physical changes as a
function of applied heat. It can be used to generate several useful
parameters, Tg, X/Y/Z axes CTE, etc.. These things seem to be of most use to
most people.

However, if I were concerned about an important PWB material transition
under heat and vibration, I might use the DMA numbers more as representing
reality under those conditions.

Maybe "one" method was never chosen because the importance depends on what
you are looking for from the test?

Not sure.

BTW - Hope you are doing well!

Regards,

Gerry



From: "valerie St. Cyr" <[log in to unmask]>
Reply-To: TechNet E-Mail Forum <[log in to unmask]>,
[log in to unmask]
To: [log in to unmask]
Subject: [TN] TMA recommendation
Date: Thu, 16 Nov 2006 14:56:52 -0500

Dear Tech Netters,

I have read that "IPC recommends" TMA for Tg determination (vs DSC or
DMA).

I have searched the site for a White Paper without finding one; I have
reread both specs looking for any language which would seem to imply one
is better than the other for determination of Tg given that the test is
one that reacts to thermal inputs, making it perhaps a more useful test
wrt to assessing thermal robustness given lead free assembly.

I am not trying to establish the differences between the tests. I am
trying to establish if IPC is on record somewhere with a recommendation or
preference.

Anyone know?

Thanks, Valerie

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