1.You may try out one method--printing solder paste followed by normal
process of gluing and reflow(curing become inclusive).The paste on pads
helps retain components and it also keep components falling off in
subsequent operations.
2. You might need to measure and control HASL thickness and bump zenith.
3.Multiple dots of glue instead of single glue dot may help particularly
components with wide area.





> ----------
> From:         Larry Morse[SMTP:[log in to unmask]]
> Sent:         April 1, 1997 12:12 PM
> To:   [log in to unmask]
> Subject:      Re: [TECHNET] SMT Coplanarity issues
>
> Steve,
>
> It appears that you have several options.  One would be to change to
> an
> alternate board finish, such as an OSP, immersion gold, palladium,
> etc,
> which all have very flat surfaces.  HASL  thicknesses vary
> considerably,
> especially those processed vertically.  A "typical" HASL specification
> is
> something like .00008" minimum to .002" maximum.  If you're seeing
> ranges
> outside those, perhaps the HASL process can be improved.
>
> Another option may be to find an epoxy with a higher green strength,
> in
> order to hold the components more consistently before curing.  Or is
> the
> mis-location actually due to the surface finish at all, or is it that
> big
> crack in the concrete that the operators roll the cart over on their
> way to
> the curing oven?  Or the servo ramp rate of the movable worktable on
> your
> placement table... Or.... Or...
>
> Just some thoughts.
>
> Larry Morse
> Celwave RF
>
>
>  ----------
>
>  ------------------------ INTERNET MAIL ------------------------
> From:           Steve Collins <[log in to unmask]>
> Subject:        [TECHNET] SMT Coplanarity issues
> Date:           Fri, 26 Sep 1997 08:41:01 -0600
>
> ----------------------------------------------------------------------
> -----
>
> Werner thanks for the response but our problem is not shelf life but
> rather
> the ability to place surface mount components on a dot of glue
> consistently. What we are seeing is a variation of up to several
> thousandths of an inch in pad height. Our vendor has done the required
> tests to J-STD-003 and he complies to the solder float test for
> solderability.
>
> Is there a specific test that the vendor can do to ensure that this
> phenomenon go away. Our vendor has stated that his pressure on his hot
> air
> knives on the HASL equipment is low and that this may contribute to
> the
> problem. But I don't think anyone can state for sure that this is the
> problem.
>
> My curiosity is does any one else suffer from this problem and what
> steps
> have they instituted either in house with their processes or at the
> fabrication shop to reduce this abnormality. Is this something that is
> a
> fact of life with fine pitch components.
>
> _______________________________________________________
> Hi Steve,
> In order to preserve solderability fot longer shelf lives, the solder
> layer
> after HASL is best at 5 micro-meters and above. Less solder will have
> increasingly shorter solderablility shelf lives depending on storage
> conditions.
>
> Werner Engelmaier
> Engelmaier Associates, Inc.
> Electronic Packaging, Interconnection and Reliability Consulting
> 23 Gunther Street
> Mendham, NJ  07945  USA
> Phone & Fax: 973-543-2747
> E-mail: [log in to unmask]
>
> ___________________________________________________________
> What is the proper amount of solder that should be on an SM Component
> pad
> after HASL. IPC calls for "Coverage and Solderable" but what does this
> really mean. My curiosity is sparked by our entry into the fine pitch
> arena
> and our vendors ability to give production what they need.
>
> I have gone back to our internal production people and requested that
> they
> supply us with their requirements.
>
> Steve Collins
> PCB Design Supervisor
> Antec Network Technologies
> [log in to unmask]
>
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