A CAREFUL operator should be able to place masking +/- .030".  Don't forget
your material tolerances as well.  I figure +/- .015 for any off the shelf
stuff, +/- .005 for any custom die-cuts.

Kevin Glidden
Manufacturing Engineer
Luminescent Systems Inc.

 

-----Original Message-----
From: Whittaker, Dewey (EHCOE) [mailto:[log in to unmask]] 
Sent: Tuesday, November 13, 2007 1:42 PM
To: [log in to unmask]
Subject: Re: [TN] Conformal Coating masking tolerance

+/- 0.8 mm
Dewey

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Joe Macko
Sent: Tuesday, November 13, 2007 10:48 AM
To: [log in to unmask]
Subject: [TN] Conformal Coating masking tolerance

Good morning Techs.

 

We are redoing our conformal coating and masking process instructions for
double sided boards and was asked to revisit the tolerance for masking up to
keepout surfaces/edges. For example, many of our boards have a ~ ¼" wide
keepout zone around the perimeter that is defined by a gold edge. Typically,
the operator will mask up to the edge with an ESD tape and than spend
non-value added time touching up after de-masking if the c/c does not come
right up to the edge.  

 

As far as I know, IPC is silent on this type of masking question so I was
wondering what the industry consensus on a realistic masking tolerance is.
A few CMs have told me that they typically hold from 0 to .060" up to 1/8"
provided ALL components and SJs are coated and that there is solder resist
up to the edge of the keepout surface.  I would think that something less
than 1/8" like .060" is achievable and cost effective without compromising
the reliability of the board as long as ALL components and SJs are coated
and there is solder resist up to the edge of the keep out surface.   Please
let me know what other users use as realistic masking tolerance without
compromising the reliability of the board/coating.  Thanks

 

Best Regards,

- Joe

 


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