I agree that a bd mfr. *can* correct for silk on pads (not just SMT but vias
and other features), however, this can be costly, must be done for every
lot, will vary from bd shop to bd shop, and most importantly, you may lose
important info from the PCB.  Your designers should inspect the layup of the
silk, and exterior layers for these issues and correct them at the design
level.
     We had problems with this until our PCB shops told us their
registration requirements for silk, which we then incorporated into our
database.  It has become a rare occurrence since then.
 ----------
From: TechNet-request
To: louh
Cc: technet
Subject: Re: FAB:  Silk-screen ink on surface mount pads
Date: Tuesday, May 28, 1996 8:42PM

[log in to unmask] wrote:
>
> Recently I have seen PC boards with silk screen ink on surface mount
> pads.  Is any of this allowed?  Looking at the PC board IPC standards, I
> don't see this subject addressed.  May I have some guidance?
> Lou Hart   412-858-6117
>
> .I am not sure about I.P.C standards but it is not recomended.
Your board manufacturer should take care of this for you.
Being involved in the photo dept and plotting end of board
manufacturing we do not allow screening to land on any pad or surface
mount area.
To avoid this
 - using your plotter ,plot your soldermask as a negative on top of your
silk screen
 -on the cam ,use the clear silkscreen option using appropriate mask to
clear yor silk
 -in darkroom shoot a negative of your silkscreen and a positive of the
soldermask.  merge them togeather using a contact in the dark room
you will be left with a positive of your silkscreen with pad and surface
mount free of ink.(the old but still works way)
 -