Parvez,
        You're absolutely right.  Re-flow parameters are certainly critical,
especially with sensitive paste.  As I mentioned (not very well),
improper re-flow profile parameters can dry out the flux, or worse, burn
it.

        Recently, at SMTA, Charles Bradshaw presented an interesting paper
titled "Thermogravimetric Analysis Predictions of Reflow Profile of
Solder Pastes" that is basically a scientific method of determining the
reflow profile for any specific flux vehicle.  That paper goes into
better specifics as to what will happen to the flux for incorrect reflow
profiles.

        In addition, I neglected to mention that voids in BGA's happen only
when paste is used.  If only flux is used, the tip of the ball can begin
wetting the pad from the inside out to the edge of the pad, thus driving
the flux in front of the molten solder.


                        Thanks

Ryan Grant
Process Development Engineer
MCMS
(208) 898-1145
FAX (208) 898-2789
[log in to unmask]

>-----Original Message-----
>From:  Parvez M.S. Patel [SMTP:[log in to unmask]]
>Sent:  Monday, September 27, 1999 6:58 AM
>To:    [log in to unmask]
>Subject:       Re: [TN] BGA voids
>
>Ryan
>that was really good reply.
>Dont u think reflow profile parameters are also critical?
>
>
>
>--
>PARVEZ M.S. PATEL                             ADDRESS:
>GRADUATE STUDENT,                             APT.#2, 182 Westend Avenue,
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>BINGHAMTON-NY.
>
>PH:607-770-7507
>
>EMAIL:[log in to unmask]
>      [log in to unmask]
>
>URL:bingweb.binghamton.edu/~bg22842
>
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