Alvin,
Just let me add some comments to Steve's comments.
As a stencil manufacturer (of three technolgies) we see most of the
reductions of 10% from our customers.
For laser cut and etched we use the below mentioned rule of thumb
to stay at least 1.5 times the thickness of the stencil in the width
of the opening. Steve is correct, people today are to fast to say no
to etched stencils. Our guess is that 80-90% of the laser cut
stencils can be etched with no problems at all and at lower cost
especially with a high number of apertures, but our customers
make the final decisions on this.
With more fine pitch or longer yields most our customers switch to
electroformed stencils (nickel), less wear, less cleaning, smoother
walls and you can go down to about 1 times the thickness of the
stencil in the width of the opening. And in general we advise our
customers to decrease the stencil steickness with about 25
microns compared to the stencil thickness they use normally with
stainless steel.
I do not want to make this sound like an commercially e-mail,
espacially since we are in the Netherlands (Europe), but I feel it is
necessary to shine a light on the three technologies and the
possiblities with it. You can further discuss this off line with me by
sending me a direct e-mail or check out our website for more info
on the three technologies www.veco.storkgroup.com.
Date sent: Wed, 11 Aug 1999 19:41:30 EDT
Send reply to: "TechNet E-Mail Forum." <[log in to unmask]>, [log in to unmask]
From: "Stephen R. Gregory" <[log in to unmask]>
Subject: Re: [TN] Stencil aperture opening
Originally to: [log in to unmask]
To: [log in to unmask]
> Hi Alvin!
>
> Jorge makes some good points, but I'd like to add to his input:
>
> > Alvin;
> >
> > There is no formula since the stencil opening depends on pad size at
> PCB,
> > as rule of thumb they recommend reduce 10% from pad width to give a good
> > gasketing.
>
> 10% is not a bad percentage to reduce the apeture opening size, but most of
> the stencil houses I use will reduce the openings 20% if I ask for a standard
> industry reduction...and there is somewhat of a formula to use to keep you
> outta trouble when dealing with fine pitch apetures. You want to stay at
> least 1.5 times the thickness of the stencil in the width of the opening to
> keep from having your paste hang-up in the apetures when you're printing.
>
> > Stencil thickness generally is 6 mils, laser cut, trapezoidal
> > shape with eletropolish finish.You can use eletroformed stencil as well,
> but
> > NEVER use chemical etching type for fine pitch.
>
> Well, that's almost true. But there's a stencil company that I've used in the
> past that etches stencils in a different manner than most. The company is
> named BeamOn Technology. Their process is called "Band-width Etch" or "Band
> Etch". They actually etch only the outline of each apeture, not the whole
> opening...much easier to control that way. They don't get the typical
> "hourglass" cross section like what normally happens when etching from
> double-sided photowork...very straight and smooth sidewalls. I've had
> stencils made that contain 15.7-mil pitch devices and the stencils print
> every bit as good as laser cut stencils at less cost. You can visit their web
> site at: http://www.beamon.com. When I worked for Zevatech, we used BeamOn
> stencils for that little keychain we built and passed out at the shows like
> NEPCON, SMI, etc.
> For those of you that have one of them you know that the QFP is 15.7-mil,
> also got a microBGA, and 0402's...stencil worked great!
>
> Just thought I'd add my two-cents...
>
> -Steve Gregory-
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