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Good thing about TMA is that it will provide you both Tg & CTE information.
So does a DMA but sample prep & cost is much higher.
Rich K / GTS
847-621-7310
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Werner Engelmaier
Sent: Thursday, November 16, 2006 3:17 PM
To: [log in to unmask]
Subject: Re: [TN] TMA recommendation
Hi Valerie,
To my knowledge-and I should know since it is I who is talking up Tg(TMA)'
the IPC is not on record in terms of a preferred test method--nor should it be.
One needs to understand what the Tg represents to determine which test method
will give the better answer in a given case.
The Tg is a single-point locator for a temperature range (typically 50C or
more wide) over which the resin changes from its 'glassy' state to a 'rubbery'
state by a change in molecular/cross-linking structure. Essentially all of the
resin's properties are different in the glassy and rubbery states-one is best
served to think of entirely different materials.
Each of the three test methods [TMA, DSC, DMA] measure an entirely differtent
property of the resin, with each of them being important for different
purposes. They roughly relate to each other as follows: Tg(TMA) — Tg(DSC)-10 to
20śC — Tg(DMA)-20 to 40śC.
For reliability issues, typically driven by differential thermal expansion,
it is the Tg by TMA that is the most important.
The White Paper you are referring to is most likely the one that I have
authored, titled: "Recommendations for PCB FAB Notes and Specifications in Printed
Circuit Board Drawings for SnPb and Lead-Free Soldering Assemblies, the
Qualification of PCB Shops and Activities to Assure Continued Quality."
Werner
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