Ron,

You are not doing two things right from the information you
wrote below.  Rubber squeegees and thick stencils (0.007")
bring always a poor soldering result for the QFP (0.5 or
0.4mm pitch??).  Recommend the following:

- Use metal squeegees
- Increase stencil aperture aspect ratio, recommend
0.006" or 0.005" stencil thickness(I prefer 0.005").
- Use Au/Ni plated or OSP coated boards, HASL boards are
bad comination with 0.5mm or less pitch QFP's

Said all that, fine pitch stencil aperture size also plays an
important role.  95% to 99% yield is typical and considered a
good result.

Regards
Matthew Park


>>> Ronald Mowbray <[log in to unmask]>
January 16, 1998  9:30 am >>>
   I would like to get some information on expected yields for
non-soldered leads using 240 pin PQFPs. Is this common or
can process improvements without equipment purchases
help?. We have a FUJI GSP III screen printer with rubber
squeezes and are using 7 mil thick laser cut stencils. I could
use any help and expected yields information. We are going
to change to BGA sometime later this year.

                                                        Thanks
Ron Mowbray
Menber of Technical Staff
Paradyne Corp.
Largo, Fl.
e-mail: [log in to unmask]

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