Hi Paul,

The maximum sustained operating temperature will depend on the specific base material—IPC-4101 is mute in this regard, 
and I doubt you will find much on the specific base material data sheets.

I do not see anything in a real reliability concern at a constant T of 70C—certainly moisture is not an issue.  The prepreg layer 
layers will continue to cure to completion, which entails some changes in properties.
Also, the molecular structure of resins will change over time—this is T-dependent, which will change dielectric properties over time.
This only has consequences in very high-speed applications that have been designed to the very edge.
Werner



 

 

-----Original Message-----
From: Paul Reid <[log in to unmask]>
To: [log in to unmask]
Sent: Fri, Dec 11, 2009 3:11 pm
Subject: [TN] PWB Operating Temperatures


Hi All,


Can anyone tell me, or direct me to where I can find, the maximum sustained 
operating temperature for a PWB fabricated with FR4.

What are some of the reliability concerns, at the assembled board level, 
associated with a constant temperature of 70°C?



Thanks

Paul Reid

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