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January 1997

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From:
"David T. Novick" <[log in to unmask]>
Date:
Wed, 29 Jan 97 09:52:37 PST
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We have been working with a new surface mount line for the past year and 
are happy with the different pieces of equipment.  We process many printed 
wiring assemblies some of which have 25 mil flatpacks and quadpacks 
throughout the board.  We realize that fine pitch is not as forgiving as 50 
mil pitch and through hole technology, especially when the assembly is 
fully automated.  Our challenge is that we produce a large mix of different 
assemblies, each at low volume, which we must process through the same 
surface mount line (typical batch size 10-25 boards).  This does not help 
when trying to stabilize a process.  One of our biggest issues is
coplanarity.  In most cases we do not have the luxury of receiving these
parts preformed and, therefore, must form them internally.  The handling
does not help.

We are evaluating all factors which have an effect on solder yields in an 
effort to optimize this assembly line.  We are interested in benchmarking 
with other companies in the industry.  My first question is:

What is the typical defect rate from a surface mount assembly line, when 
fine pitch components are involved, considering the narrowness of the 
process window?

And my next two questions are:

What coplanarity reqirement do you impose?

For those doing their own component lead forming, what procedures do you 
use to assure meeting this coplanarity requirement?

Rosaura Corral-Perez
[log in to unmask]    

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