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February 1997

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Subject:
From:
"W. Scott Gaskins" <[log in to unmask]>
Date:
Thu, 20 Feb 1997 17:54:52 -0500
Content-Type:
text/plain
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text/plain (78 lines)
Jerry and others...

I am familiar with no-clean fluxes and the residue left, but this
is normally only on the leads right at the pads.  This coating 
appears to be some kind of sealant that coats the leads and over
onto the top of the parts.
 ..................
 .   ||||||||||   .
 .  +----------+  .
 . =|  ......  |= .
 . =|  .    .  |= .
 . =|  .    .  |= .
 . =|  ......  |= .
 .  +----------+  .
 .   ||||||||||   .
 ..................

The coating would be the area inside the '...' line (sort of donut 
shaped) that would cover all the leads and over-spray the top of the 
QFP.

Thanks again,
Scott Gaskins
[log in to unmask]


Jerry Cupples wrote:
> 
> Scott Gaskins asked:
> 
> >I am working on a quality team to improve our surface mount
> >assembly processes and was critiquing some SMD boards from other
> >manufacturers and was wondering why some of them are putting a
> >clear over-coating on fine pitch (.025" and smaller) parts after
> >they are attached to the board.
> >
> >It seems to me that this would limit re-work (if required) unless
> >there is some way to remove the coating.  It would also mean
> >that no probing of the parts could be done in a troubleshoot area.
> >
> >There must be some good reasons for this clear coating applied to
> >the leads.  Please let me know of any reasons all of you have!
> 
> What you describe sounds like a resin remaining from the flux.
> 
> Many of the so called no-clean fluxes, especially those which are
> more properly called "leave-on" will have a considerable residual
> which might appear as a "coating". This would of course be
> concentrated in areas where the paste was applied in the assembly
> process rather than covering the whole board.
>
>[snip]
>
> cheers
> 
> Jerry Cupples
> Interphase Corporation
> Dallas, TX USA
> http://www.iphase.com

-- 
[                     Scott Gaskins - ext. 5368                        ]
[ ----===>> GE-Fanuc, North America. ----- Hardware Design   <<===---- ]
[  mailto:[log in to unmask] |"Truth is nothing but a path traced]
[  http://gein.cho.ge.com/~wsg     |  between errors."  - F.A.Mesmer   ]

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