Just a comment for what it is worth: 

Tg is an indicator of material robustness but it is not definitive. There are high Tg materials (170°C) that are not robust in a tin/lead application if the board is fabricated with sequential lamination. 

Werner's STII method has a three parameter input (I believe) which includes Tg. His method is much better at quantifying a materials' likely hood to be robust in a given application than considering Tg alone. 

I have not heard of specifying Tg as requirement in an end use environment. Specifying a Tg minimum may not be in your companies best interest in order to guarantee a robust product in a given end use environment.

Testing material robustness is readily achieved with thermal cycle testing. Thermal cycle testing allows one to rank robustness of various materials. I know from experience they will not lineup in descending order of Tgs.

Sincerely,

Paul Reid

Program Coordinator

PWB Interconnect Solutions Inc.
235 Stafford Rd., West, Unit 103
Nepean, Ontario
Canada, K2H 9C1

613 596 4244 ext. 229
Skype paul_reid_pwb
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-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Bryan Montney
Sent: Tuesday, November 11, 2008 1:49 PM
To: [log in to unmask]
Subject: [TN] Tg specification

I'm looking for a guideline or resource (IPC spec?) on how to select and specify the proper Tg for a given design? I'm not talking about process wise (Tg140 is acceptable in our lead-free processes), but design wise.
For example, is Tg140 material sufficient for a board running 80amps through it and sitting in an enclosure on a hot summer day in Arizona?
Also, I'm looking for how best to test the Tg robustness during production. Any help would be greatly appreciated. 
 

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