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1995

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Subject:
From:
David Bergman <[log in to unmask]>
Date:
Wed, 22 Nov 1995 16:39:06 -0600 (CST)
Content-Type:
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TEXT/PLAIN (54 lines)
We have tried for years to get the Military spex to move away from a 
measurement of tin/lead or solder thickness.  This was accomplished 
several years ago.

The real issue here is solderability.  If the board was solderable and 
you didn't have any solder, that would be great.  The issue is also how 
robust is the users soldering process and how much solderability 
variation they can tolerate without seeing defects.

IPC did a major test program to evaluate the shelf life of various 
coatings over a 2 year storage requirement.  In the report IPC-TR-462 
"Solderability Evaluation of Printed Boards with Protective Coatings Over 
Long Term Storage" , the committee concluded:

"...The soldering performance exhibited by the sample boards, as 
determined by visual examination, showed absolutely no correlation to 
solder thickness or solder coverage observed in crossectioning".

The results of TR-462 were instrumental in changing the industry way of 
specifying coating thickness.

Good luck with your survey.

***************************************************
David W. Bergman, Technical Director
IPC
2215 Sanders Road
Northbrook, IL  60062-6135
708-509-9700 x340 Phone
708-509-9798 Fax
email  [log in to unmask]
***************************************************


On Tue, 21 Nov 1995, Glynn Shaw wrote:

> As fabricators, we have had it drilled into us that "flat solder is best"
> for assembly. We have never received a return from any customer for "thin
> solder", but I can't say the opposite is true. My process engineers desire
> to alter our hot air solder leveling parameters to eliminate any future
> chances of returns for thick solder. Our SPC data suggests that lowering the
> peak solder thicknesses results in exceptionally thin solder (IMO) on
> certain pad geometries. My question:
> 
> How thin is too thin? As assemblers, when (at what thickness or process
> conditions) would you return boards to the fabricator?
> 
> 
> [log in to unmask] (Glynn Shaw)
> 
> 



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