Julie,

I totally agree with you.  From all my experience in the Bell System as long as the RMA flux passes the Belcore  (now Telcorida) compliancy test we consider the flux qualified to be what we call a "Leave Behind" flux.  Every time someone in manufacturing tried to clean a "Leave Behind" flux we had problems because they typically used a solvent like IPA and washed away most of the rosin/resin leaving the ionics behind (and mobile) and leaving the trace/component exposed to moisture in the air because it no longer had a rosin/resin coating.

Regards,
George
George M. Wenger
Senior Principal Reliability / FMA Engineer
Andrew Corporation - Wireless Network Solutions
40 Technology Drive, Warren, NJ 07059
(908) 546-4531 Office (732) 309-8964 Mobile
E-mail: [log in to unmask]


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Julie Silk
Sent: Wednesday, October 12, 2011 12:09 PM
To: [log in to unmask]
Subject: Re: [TN] ORH1 flux residues

At Agilent, we strongly advocate for leaving on RMA flux residues from wire solder and not attempting to clean them.  We have a "tech notes" paper from 40 years ago explaining that RMA flux residues provide good SIR and long term reliability.  And that RMA residues that are cleaned with a spot-cleaning method are damaging, spreading residues over a large area of the board and under low clearance parts and lowering SIR.  In the field or in our factories, we don't have access to automated cleaning equipment to do a thorough job of cleaning.  I've found that only pretty harsh methods will thoroughly clean RMA residues, and I do believe that partially cleaned residues are more contaminating than undisturbed residues.  Our rules are:  Leave on RMA, no tacky flux residues allowed, if you remove it you have to remove all of it with an automated process as one of the steps, no liquid flux for hand-soldering (which only deactivates with the heat of soldering, which won't happen with point-to-point soldering).  The "leave on RMA flux" may not be satisfactory for military or aerospace, but for our products it works and has for decades.

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