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October 2005

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From:
Joyce Koo <[log in to unmask]>
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Date:
Thu, 13 Oct 2005 17:33:48 -0400
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I thought SAC use ramp-to-spike...not ramp-soak-spike...may be just silly
me...jk

-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Jason Gregory
Sent: Thursday, October 13, 2005 5:05 PM
To: [log in to unmask]
Subject: Re: [TN] SAC reflow profile and flux vaporization


Leo,

I use a different mfr. of SAC305 but I stay in the 60-90 sec for the
150-170c part of the profile. It works great for me. 160 seems very
excessive. Also, the 365 sec from ambient to reflow is long too. I stay with
4-4.5 min. (10 zone, 14 in. zone lengths at 32 ipm). If we find voiding at
the 5DX, I slow to 31 or 30.

Are they using ramp-to-spike or ramp-soak-spike?


Jason Gregory
Manufacturing Engineer
Innova Electronics
(281)653-5593
(281)653-5594 fax
(281)212-0844 cell
[log in to unmask]

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Leo Higgins
Sent: Thursday, October 13, 2005 3:51 PM
To: [log in to unmask]
Subject: [TN] SAC reflow profile and flux vaporization

Hello,
     I have a case where a customer may be running an inappropriate reflow
profile for surface mounting on a board with and OSP pad finish.  The
time/temp features of the profile push up against every min or max in the
recommended IPC reflow profile for SAC.  The surface mount solder is
Sn-3Ag-0.5Cu (Senju 705).  The time from 150-200C is 160 seconds (seems way
too long).  The time from RT to peak is 365 sec.  Time above 220C is 57
seconds.  The solder shows wetting to the leadless contact on the package
and to the board, but temp cycle life is much less than normal.  Solder
joint cross-sections show a atypically grainy structure and some show
microvoids dispersed across the joint.  Looks to me like the flux was
vaporized before liquidus was reached, resulting in poor coalescence of
solder particles, further aggravated by a low peak temp of 234-235C.  The
discussions about good SAC wetting on OSP needing 235-237C from Steve at
ClearCube add further concerns.  The solder joints were somewhat
hour-glassed in cross-section so virtually all failures occurred through the
waist of the solder joint, so the impact of poor wetting was not seen, but
is not doubted.  I think there are a number of possible problems with this
profile.  Any comments?  Specifically do you think the 160 sec. from
150-200C could have vaporized most of the flux?



Best regards,
Leo

Director of Applications Engineering
ASAT, Inc.
3755 Capital of Texas Highway, Suite 100
Austin, Texas     78704

ph     512-383-4593
fx      512-383-1590
[log in to unmask]
www.asat.com


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