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August 2003

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Subject:
From:
Werner Engelmaier <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Mon, 4 Aug 2003 13:20:55 EDT
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In a message dated 08/02/2003 0:50:34, [log in to unmask] writes:
>By now I have seen quite a bit of ATC presentations for Lead Free and I am
>a bit surprised that this is the first time I have read about a soak or
>dwell time at each temperature extreme. Most have reported that they just
>go up and then back down in temperature. 30minutes up and 30 minutes down,
>thus 24 cycles a day across the range they have selected seems quite common.
>Any comments??
>Have you also seen this type ATC procedure?

Hi Dave,
Yes, unfortunately I have seen them--and it's a pity. These data are worse
than useless--they are misleading. But that comes from people doing things
without understanding them, and from people being pushed to produce data
fast--nevermind that they are meaningless.
As an example of this, just look in the Circuit Assembly magazine, July 2003, 
page 25, in "The Cost of Going Green," [we all know by now the going 
lead-free is anything but 'Going Green'], where the author Alan Rae, cookson 
Electronics, Inc., states under the heading 
"What is the reliability compared to eutectic solder?"
We tested reliabilty--air-to-air, liquid-to-liquid--between 550°C and 1250°C 
[I would think he meant -55 and 125°C]. We found no major difference between 
the alloys and surface finishes, but we did find that large resistor components 
(1206) failed frequently due to joint cracking under thermal stress."
Using thermal  shock tests with no hold times is put forth as proof that 
LF-solders are not different than Sn/Pb solders. 

Regards,
Werner Engelmaier

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