Werner,
Ok, that makes sense. My "Gut Level Feel" was about 100C, just based on
seeing boards from the field. I never thought about the RANGE of the glass
transition process.
These tiny switching regulators in small QFN packages run really hot. All
the design notes have vias in the center thermal pad to help conduct heat to
the lower layers. If barrels are going to be cracking that will push case
temps even higher.
This use of vias to conduct heat from HOT case temps sounds like a less
than perfect solution.
Thank you
Bob K.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Werner Engelmaier
Sent: Thursday, October 21, 2010 3:06 PM
To: [log in to unmask]
Subject: Re: [TN] FR4 Temperature and Life
Hi Bob,
With your application you want to have a Tg of at least 150C-you need to
remember that glass transition is a process that takes place over about a
50C temperature range; so for Tg=150 it starts at about 125C.
The biggest issue most likely will relate to barrel fractures.
Werner
Upcoming workshops:
November 2 & 9, SMTA Webtorial,
"Fundamentals in Solder Joint Reliability"
December 7 & 14, SMTA Webtorial,
"Acceleration Models, Accelerated Reliability Tests and
ScreeningProcedures"
-----Original Message-----
From: Robert Kondner <[log in to unmask]>
To: [log in to unmask]
Sent: Thu, Oct 21, 2010 1:12 pm
Subject: [TN] FR4 Temperature and Life
Hi,
I was looking around and I found some references to "FR4" as having a Tg
from 100 to 130 C. I was surprised as I thought that seemed low.
Now I understand that FR4 is a pretty wide brush and it covers a lot of
different materials and different suppliers. BUT, I was wondering what
"Most" PCB vendors are supplying and how the Tg affect life with hot
components.
I have some small QFN parts that tend to run hot, PCB temps of 100C or a
little more. Forgetting thermal cycling for a moment does a 100 to 120 C
temperature induce failures in other area like copper foil to base
separation, de-lamination, solder interface or any other failure mode?
Any pointers to literature?
Thanks,
Bob K.
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