my experience is the same as John's on this issue
i.e. do open it up

we once shipped a board to fab and forgot to do this
they called us up and advised that we do and used a descriptive 
term (opening up the mask) which i can't recollect

it wasn't 'block' but i can't recall it, something like 
'moat' or 'bar'?

any one know the common term ?

Dennis Saputelli



"John A. Ross [RSDTV]" wrote:
> 
> > -----Original Message-----
> > From: Tom Robinson [mailto:[EMAIL PROTECTED]
> > Sent: Tuesday, December 16, 2003 9:26 PM
> > To: Protel EDA Forum
> > Subject: [PEDA] Solder mask...
> >
> >
> > Is it ok to block open the solder mask on gull-wing i.c.'s with .4mm
> > AND .5mm pitches?
> >
> > It seems to get enough web in between the pads to stick will cause a
> > LPI registration thats too tight, with possible smearing. And if you
> > make the pads themselves too narrow -- thats another problem.
> 
> Tom
> 
> I always block open the pads on these pitches.
> 
> It is not so easy to get a manufacturer to get SM registration right at
> these tolerances although it is possible.
> 
> Most quick turn boards I have had to take as 'free issue' parts to assemble,
> which have not blocked off these areas, I have had quality issues with the
> finished joints around these fine pitch pads.
> 
> I have never had an issue with blocking them open, biggest solder mask issue
> I have ever had was when the SM thickness to finished pad height
> differential was too much (SM height was bigger than finished pad by a lot)
> and we had gasketing issues from the paste screen to the pad, causing
> problems like, paste bleeding out on the PCB side of the screen, some
> shorts, failed 3d inspection after print cycle, loose solder ball symptoms
> and aperture blockages, with our MPM printer having to make undue clean
> cycles between prints. Also undue print down force had to be applied to
> squeegee blades, increasing wear and decreasing accuracy.
> 
> Never had solder ball or short issues as long as the board is printed
> correctly and the oven specifically profiled to suit your board. (also
> optimise paste volumee, height, reductions...)
> 
> John

-- 
_______________________________________________________________________
Integrated Controls, Inc.           Tel: 415-647-0480  EXT 107 
2851 21st Street                    Fax: 415-647-3003
San Francisco, CA 94110             www.integratedcontrolsinc.com


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