Ron,

     Quickly,

     1. Are the leads truly non-soldered or are you having solderability
        problems from the leads.  Look at the component date codes.

     2. What type(s) of solderpaste are you using?

     3. If you feel you are not getting the appropriate amount of
        solderpaste volume and do not have or want to procure additional
        capital, try the following.

        -Re-define the aperture openings in you stencil.
        -Laser cut the stencil
        -Trapazodial finish via cross-sectioning
        -maybe a .006"thk, should be OK for a .020" pitch

        Call me for more specifics.

     4. Re-evaluate your Z-axis placement force, if applicable to your
        equipment.  Allow the head to seat the component in the solderpaste
        vesus laying or dropping it on top.

     5. There is no or minimal control with regards to QFP coplanarity.  Do
        your best and impose processes on to your suppliers, especially
        when it comes to component retentions periods.

     6. Definitely move away from using a polymer squeegees.  Forget using
        a durometer to measure the squeegee hardness and go with a
        stainless steel squeegee.  Unless you have stepped stencils, which
        I do not care for, there is no need to have the rubber.

     7. Monitor your solderpaste carefully and try using an OA (organic
        acid flux) versus no clean.







______________________________ Reply Separator _________________________________
Subject: [TN] Poor Soldering of 240 pin PQFPs more info
Author:  Ronald Mowbray <[log in to unmask]> at Internet
Date:    1/16/98 2:48 PM


   I would like to get some information on expected yields for
non-soldered leads using 240 pin PQFPs.5mm pitch. Our
yield is 25% or more bad circuit cards on average. The lead
coplarity ranges from 0 to 3.5 mils with most falling in at 2.5
to 3.5 mils. 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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