Carl,
I recommend Omikron white tin for finish. I have no experience with type 4
powder. If this is no-clean, I recommend the home plate aperture. If not,
then regular aperture design. I do recommend 10% reduction. I also
recommend K&J Marketing stencil, called Kepoch. It is a kapton-type
stencil. The material "melts" as it's being laser-cut, giving an absolute
mirror like finish in the aperture walls. Your release problems will vanish
like magic. They are out of Canada somewhere. I used to have their contact
info, but it's long gone now. Do a web search. The price is same as
stainless and they have 24 hour turnaround. These are very durable. In a
former life, I switched to these screens and was EXTREMELY impressed.
My .02 cents.
Jason Gregory
SMT Production Supervisor
LaBarge Inc.
(918)459-2367
(918)459-2221 fax
[log in to unmask]
http://www.labarge.com
Carlr Ray
<Carlr.Ray@SANMIN To: [log in to unmask]
A-SCI.COM> cc:
Sent by: TechNet Subject: [TN] 16mil QFP Process Issues
<[log in to unmask]>
02/17/03 04:25 PM
Please respond to
"TechNet E-Mail
Forum."; Please
respond to Carlr
Ray
Hey Techneters,
I have a couple of questions you guys maybe able to help with (at least
I want some advice). The questions below pertain to some assembles I
will be developing some processes for in the near future. These units
have the following technology: 16 mil QFP, uBGA .65 mil and 1 mil pitch,
multiple PBGA 300+ ball count, PTH components (radial and axial types),
double sided, HASL surface finish.
1. For 16 mil QFPs and uBGAs .65 I would like to see a different
surface finish (Immersion Silver?). What do you guys think?
2. Solder Paste. I have used type 4 powder mesh size (-400+635) in the
past but not much success. Who has had success with type 4 and who was
the vender?
3. Stencil Apertures. I know the industry recommends 4 to 5 mil stencil
for this application but what other techniques have you "wizards" tried
in the past? I have tried step downs, dog bones, bow tie, home base
plate, 10% and 20% reductions and various combinations. My biggest
concern is developing the process and stencil around the 16 mil
component. I also have seen success with Nickle plated aps to aid with
release for the super fine pitched devices.
Thanks in advance guys and gals!!
Carl Ray
Sr. Manufacturing Engineer
Huntsville, AL 35807
Phone: 256-882-4800 ext. 8845
Cell: 256-990-1990
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