9 Jul
2007
9 Jul
'07
10:05 p.m.
On Mon, 9 Jul 2007, jd wrote:
Date: Mon, 09 Jul 2007 06:22:00 -0700
From: jd <onymouse at garlic.com>
Reply-To: "General Discussion: On-Topic and Off-Topic Posts"
<cctalk at classiccmp.org>
To: General at bakaboy.onymouse.net,
"Discussion at bakaboy.onymouse.net": On-Topic and Off-Topic Posts
<cctalk at classiccmp.org> ;
Subject: Re: trace wrinkles
William Donzelli wrote:
No. The differences in expansion just are not that big. If you do the
math, you will see that the dimensional changes of the the two
disimilar substances just are not that big - way too small to cause
all sorts of wrinkles. At worst case, maybe *a* wrinkle would show up
on a long trace.
The differences are enough for many thermal cycles over a long period of time.
It seems that the greater the temperature delta and the more frequently the temp
is cycled the sooner it occurs.
I've seen boards cycled between 20 and 300 degrees C five times a day that have
wrinkles in about a year and trace lift by five years. I've seen similar
wrinkling in boards cycled between 7 and 98 degrees C hourly that have been in
service for as long as 20 years. Interestingly, the boards that are at a (more
or less) constant 200 to 300 degrees C show no wrinkling or trace lift.
300 C is way above the melting point of even RoHS compliant solder, if you
temperature cycled a standard PCB to that temperature, "wrinkles" would be the
least of your troubles...
Peter Wallace
From what I've seen, this is caused by the copper
and the base material
expanding and shrinking at different rates. It is seen quite
a bit where
temperature ranges between extremes, especially with cheap and older
stuff.