Howard,
It has been my experience (using a different brand NC from the one you
mentioned), that the majority of mid-chip solderballing occurs from using
the wrong profile. Usually this happens because you are ramping up too
slow. If the solder paste manufacturer recommends the premium peak reflow
time occurring at 2.7 minutes, and you are reaching peak at 4 minutes, you
will see the problem you described. Also, try using a "ramp" profile,
instead of a "soak" profile. As for specs., see IPC-A-610 Rev.C, Section
12.4.10, Page 12-88 - "SMT Soldering Anomalies - Solder Balls/Solder
Fines".
Hope this helps. Good luck.
Regards,
Michael Sanders
Howard Watson
<howard.watson@A To: [log in to unmask]
METEK.COM> cc:
Sent by: TechNet Subject: [TN] Solder Beads (the dreaded
<[log in to unmask] little beasts)
>
10/11/2000 09:05
AM
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Hello all,
I just subscribed to TechNet, and I have to ask about solder beads,
particularly mid-chip. Here is our process:
1. Solder paste: Multicore NC40, no clean, 53-38 um particle size.
2. Vitronics XPM-820 convection reflow oven.
3. Mydata MY-15 pick and place.
4. Dek Infinity 265 screen printer.
5. Stencils are 6 mil (some are still 8), with 10% reduction and homeplate
designs for chip components.
Solder beads still are a part of the process, even after some process
improvements. There may be a higher incidence of them in the summer when
the humidity is high due to the operation of the swamp coolers, but I
haven't been here long enough to validate this assumption. My question is,
do other people live with solder beads? What is acceptable?
Howard Watson
Manufacturing Engineer
AMETEK/Dixson
Grand Junction, CO
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