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August 2001

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Subject:
From:
Guy Ramsey <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Thu, 23 Aug 2001 13:45:44 -0400
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We have done some underfill here, very limited quantities will no clean
fluxs. These were 5 mil parts with 2 mil balls. It depends who you talk to
there are advantages to cleaning but there are also problems. We had
reasonable success with the no-clean process.

IMHO, Even if you get the semi-aqueous solvent under the part, how can you
rinse it out? We use Vigon A200 in out inline cleaner and Kyzen Ionox I3330
in our batch cleaner. I have seen residue under large BGAs after cleaning.
Both are excellent but the water rinse just won't go into tight places.

If I was going to try this I think I would experiment with the HFE in a
co-solvent process. But it's expensive, requires modern equipment and good
process monitoring.

Guy Ramsey
Senior Lab Technician / Instructor


E-Mail: [log in to unmask] <mailto:[log in to unmask]>
Ph: (610) 362-1200 x107
Fax: (610) 362-1290



-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Lambert, Katherine A.
Sent: Thursday, August 23, 2001 12:00 PM
To: [log in to unmask]
Subject: [TN] Cleaning under BGAs


Hi folks,

We're embarking on something new.  We will be assembling boards with BGAs.
Some are small and fine pitch, others are regular pitch but quite large
(40mm square).  We will be underfilling them with adhesive.  Because we're
underfilling, we have to clean the flux from underneath the parts.  We're
using an RMA flux based solder paste.

Now for the question - how should I clean the flux from under these parts?
Any clues as to which solvent to use?  Any ideas on what type of equipment
to use?  I have at my disposal an in-line semi-aqueous cleaner and a vapor
degreaser.

Thanks for any insight.

Kathie Lambert
Process Engineer
Northrop Grumman
Baltimore, MD
410-765-9746

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