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January 1998

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Subject:
From:
Matthew Park <[log in to unmask]>
Reply To:
TechNet Mail Forum.
Date:
Tue, 6 Jan 1998 09:05:01 -0800
Content-Type:
text/plain
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text/plain (76 lines)
Krishna,

Bottom side SMT components are held on by solder tension
during the second phase of reflow.  First check you have
good and acceptable solder fillets for the first reflow.  A lot of
cases, there are insufficient solder tension to hold
components during the second reflow mainly due to small
SMT lands to form adequate solder fillets.  Redesigning SMT
lands and patterns solve components falling off during the
second reflow.

Also, you may need to adjust the second reflow profile
(different from the first reflow profile) for an optimum reflow
time.  I would say minimize the second reflow time to 30s
and not to exceed 210'c peak temp.

The best way to prevent components falling off is
"print-glue-pick'n place-reflow the first side" and "print-pick'n
place-reflow the second side".  And keep large and heavy
components on top side for the second reflow.

regards
Matthew Park


>>> Krishna Kalyan <[log in to unmask]>
January 6, 1998  7:15 am >>>
Hello :

 Happy New Year to all of you.

 I am a process engineer trying to resolve the falling of a
bottom side
surface mount component during second pass of forced
convection reflow.
I am beginning to feel that the solderability of the component
leads is
getting reduced after the first pass of reflow and that is
causing the
part to fall. If any of you have had similar experiences, could
you
please share ? Your suggestions are welcome.

Krishna Kalyan


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