Hey Ryan,

As far as 20 mil printing is concerned I would say type 3 i.e (-325/+500)
should be ok. If you go for type 4 ( i.e -400/+500 ) it has some issues like
the particle size getting smaller will increase the surface area exposed to
oxidation affecting the soldering quality. Also it would be expensive than
type 3.
If you are laready printing 20 mils with type 3, why you want to switch to
trype 4?
As far as more mass is concerned the volume of the paste will remain same
irrespective of particle size.

Thanks..
Ashok
SMT Engineer
Solectron Corp.
Milpitas

> ----------
> From:         Ryan Jennens[SMTP:[log in to unmask]]
> Reply To:     TechNet E-Mail Forum.;Ryan Jennens
> Sent:         Friday, May 14, 1999 11:11 AM
> To:   [log in to unmask]
> Subject:      [TN] FW: Fine Powder Solder Paste
>
>
>
>       -----Original Message-----
>       From: Ryan Jennens [mailto:[log in to unmask]]
>       Sent: Thursday, May 13, 1999 11:51 AM
>       To: TechNet
>       Subject: Fine Powder Solder Paste
>
>
>       What stencil design guidelines differ when one decides to go with
>
>       a -400/+500 particle size solder paste? The paste companies tout
> that the
>
>       finer particle paste offers print improvements below 20 mil pitch.
> But I
>
>       believe one would have to reduce the aperture sizes all around
> because more
>
>       metal would be deposited in each one. Is this accurate? How much
> reduction
>
>       is needed. Is home-plating the apertures even more important? I
> could not
>
>       find this topic in the archives. We are considering switching for
> our
>
>       finer-pitch boards, as their pitch decreases, if it really offers an
>
>       advantage. However, we have been printing 20-mil for a long time
>
>       with -325/+500 paste for quite a while.
>
>       -Ryan Jennens
>
>       TelGen Corporation
>
>

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