From: Russ
Sent: Wednesday, March 10, 1999 4:02 PM
To: 'Manish'
Subject: RE: [TN] Dull Solder Bump


Hello Manish,
Guess what?  The cleaner your DI water the worse the problem.  Get some
hot, very pure DI water and just try a quick test.  The DI water will
etch away the solder until you have no bump left.

Also watch out for flux left on the wafer after reflow.  Most water
soluble fluxes are organic acid based and can still have some pretty
good activity left in them even after reflow.

Fast cooling, no vibration, cool DI water spray rinse (without
recirculation), Hot clean DI (short time only) should have your bumps
shinning pretty.  Of course most of this is purely cosmetic.
Solderability shouldn't be impacted by by the dull solder appearance.

Regards, Russ Winslow

Six Sigma
1940 Concourse Drive
San Jose, CA  95131

[log in to unmask]
http://www.sixsigmaservices.com





-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Manish
Sent: Wednesday, March 10, 1999 2:58 PM
To: [log in to unmask]
Subject: [TN] Dull Solder Bump


Hello Everyone:

I am trying to design am experiment to study the surface appearance of
solder bumps and its effect on the shininess/dullness of bumps.  One of
our customers recently reported an increased rejection rates at their
placement machine as the dull solder bumps were not recognized.

Although we have not conducted extensive experiments in house to study
the
effect of reflow profile, cooling rate and the flow of nitrogen etc., i
would appreciate feedbacks regarding your experience with this issue.

We also rinse our wafer lots with DI water after reflow.  Is there a
possibility of impurities in DI water attacking the surface of eutectic
solder. All of the wafers we bump are near eutectic solder alloy
composition.   The issue of dull solder bumps seems to be a periodic
issue,not surfacing regularly.

I would appreciate your comments on factors responsible for causing dull
bumps.

Regards
Manish

PS I am only refering to the occurence of dull solder bumps after wafer
reflow.  We use a water soluble flux during the wafer reflow.

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