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Reply To: | TechNet Mail Forum. |
Date: | Wed, 27 Aug 1997 19:28:41 -0700 |
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If the epoxy is trying to expand in x and y, wouldn't that set up force
against the holes, causing compression?
The drilbert
Leslie O. Connally wrote:
>
> Hi Werner,
>
> Your comments to Chris were Interesting and I agree for the most part, but I
> have a question with regard to the comment about radial barrel compression
> during elevated temperatures. It is my understanding that as the board expands
> in X & Y that the hole will also increase in diameter. Due to the
> disproportionate difference in CTE I would expect that the barrel would be in
> tension and not in compression (a hoop stress). This phenomena has been
> demonstrated in the Physics classroom on many ocassions with Ring and Ball
> apparatus. It's good to see you responding to some of these interesting
> problems showing up on Technet. So what do you think about this analysis?
>
> Les Connally,
> [log in to unmask]
>
> > From: [log in to unmask], on 8/22/97 5:48 PM:
> > Hi Chris,
> > If you get the ITRI Report 'PWB Hole-To-Land Misregistration: Causes and
> > Reliability, Project Final Report", you may be a little careful in applying
> > the conclusions. I am not saying that the conclusions are wrong, but that
> > based on the test performed, the conclusions may be a stretch. From a
> > reliability point-of-view of the PTH barrel-to-land interconnect, the most
> > severe loading occurs during excursions to soldering temperatures not
> > thermal
> > cycling, even from -65 to +125C. That is because the largest thermal
> > expansion of the epoxy that causes the radial barrel compression and land
> > rotations occurs only at temperatures above Tg.
> >
> > Werner Engelmaier
> > Engelmaier Associates, Inc.
> > Electronic Packaging, Interconnection and Reliability Consulting
> > 23 Gunther Street
> > Mendham, NJ 07945 USA
> > Phone & Fax: 973-543-2747
> > E-mail: [log in to unmask]
> >
> >
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