I am not sure if this helps or not. Surely it is a question of whether the
thermal
stress is cumulative or reversible. Consider stretching metal; if you do
not exceed the elastic limit it will return to original size, if exceeded it
will remain stretched. This must also apply to other forms of stress. The
key factor is how high a temperature is the laminate taken to and what is
it's tolerance limit? If there is a cumulative effect on the material, what
is it?

Laminates are moving to higher Tg's and so thermal tolerance must be
increasing. I think the key question is how good is the copper plating in
the holes.
This is where breakdown could occur after multiple thermal cycles unless
quality is well controlled.

Paul Gould
Teknacron Circuits Ltd
UK
www.teknacron.com


-----Original Message-----
From: Asbell <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Date: 28 November 1998 00:46
Subject: Re: [TN] HASL
>===========================================================================
===
>
>Hi Werner
>
>An answer to your question in just two words.
>
>        [[[[[[[[[[[[[[[THERMAL STRESS]]]]]]]]]]]]]]]
>
>Hope this helps.
>
>Franklin D Asbell, CQA
>Network Circuits, Inc.
>Irving, Texas

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