Earl,

Do you find the bottom side temperature of 250C to be consistent across all
the rework stations you mentioned?  I'm curious, because I have an SRT unit
and have been having some difficulty with some large TI DSPs with attached
heatsinks.  I've been working with 220 - 230.  Based on your experience, do
you think 250 might be something I should try?

Thanks,

Rick Thompson
Ventura Electronics Assembly
2665A Park Center Dr.
Simi Valley, CA 93065

+1 (805) 584-9858 voice
+1 (805) 584-1529 fax
[log in to unmask]


-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Earl Moon
Sent: Tuesday, July 13, 1999 7:55 AM
To: [log in to unmask]
Subject: [TN] BGA rework


Nick,

I can't get through, as usual for me, to the IPC forum. Therefore, I'll
simply reply
with not such a simple answer.

It has taken me over a year to "get used to" various rework systems. I have
used
Conceptronic, Air-Vac, and now the SRT system. I've never used your system.

For the past 6 years I have worked extensively with every type BGA device
known
to man. I have worked with 4-30 layer boards. I have profiled my ass off
with mostly
"automatic" equipment. From all this work, I can say it would be a wonder to
me if
anyone successfully (consistently) would be able to work without aid of a
computerized
system even though very active individual interaction is required.

I really believe no one system has all the answers, but must have some
simple, but expansive,
elements in place. Now, I could go on with this, but time and drive space
doesn't permit. To this
end, I'll be happy to send you a very large article I'm finishing for
SMTnet's new on line
magazine. The finished article will appear in August's issue. Precluding
that, I provide the
following:

1) Replacement/reflow profile derived partly from removal profile
2) Reflow profile usually hotter than removal
3) Top side heater temperature usually between 265 and 290 C.
4) Bottom side heater temperature usually at 250 C (air) at about 1.5" below
board
5) Initial "soak" time about 100 seconds
6) Equilization zone about 100 seconds
7) Recomended solder paste profile used (for me not more than 100 seconds in
183 limits
   and not more than 45 seconds in 205 zone with a peak temp not exceeding
220 C.)
8) Solder paste preferred and applied using micro stencil with apertures
about 3 mils larger
   than pad diameters
9) Paste flux application acceptable instead of solder paste - not liquid
(no compliance
   achieved)
10)Must have complete ball collapse (using eutectic balls) and completely
aligned device edges
   with respect to silkscreen outline - just as in initial reflow
11)The rest is visual, metron mirror, magnification, and/or x-ray with no
unacceptable conditions
   you describe.

I'll provide any additional help you need,

Earl Moon