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June 2005

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Subject:
From:
"Stadem, Richard" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Stadem, Richard
Date:
Mon, 27 Jun 2005 15:52:48 -0500
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David,
I know exactly the residues of which you speak, and the reaction from the OA flux. 
No-clean does have a small amount of organic residues, these are supposed to be activated and inerted during the reflow cycle, but not 100% of it is. When OA flux hits it, there is a strong reaction between the two.
This is why many military and hi-rel contractors do not use it, but that is another subject.

To get the old residues off, what I have done in the past that has worked really well is to use a 13 part mix of de-ionized water to one part of saponifier, either Bio-Kleen or the Alpha Metals 2300 series. Use hot 150 deg F. water from your de-ionized water supply, and use an ultrasonic cleaner, such as the Crest Ultrasonics Corp. machines that can keep the solution at 90 deg. F. minimum. Do not go hotter than 150 deg. F.
Clean for only 10-20 minutes in the ultrasonic cleaner. If you leave them in longer than 1 hour the solderability will begin to diminish.
Follow this with a really good rinse of hot de-ionized water to get all of the saponifier off.

Ideally, if the no-clean flux on your parts have never touched plain or de-ionized water alone, or alcohol alone, that is better. There is a chemical reaction that occurs when no-clean and RMA flux contact water without benefit of saponifier added, or alcohol. That is where the white residue (called white mongue) occurs.
Anytime a no-clean flux must be cleaned, such as when a misprint occurs on the stencil, this 13:1 mix works really well for cleaning, without having the white mongue show up on the stencils or the boards. They come out really clean.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of David Tremmel
Sent: Monday, June 27, 2005 11:00 AM
To: [log in to unmask]
Subject: [TN] Flux residues

Technetters,

I have received some microBGAs which I have to reball and they have a no-clean flux residue which is difficult to remove.  Also, when it comes in contact with our water-soluble flux it creates an acid which is not very 'friendly' to the part.

Would any of the chemical gurus care to edify one of the uneducated ones why no-clean flux, when dried and allowed to set for a couple of months is so difficult to completely remove and what possible acids or chemicals are created when it is combined with water-soluble flux (type ORM1)?

As always, I appreciate the responses I receive.

David Tremmel
Technical Manager
BT Mexico

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