Hello Victor,

Solder paste fluxes are not created equal.  Different combinations of ingredients are used by each manufacturer, although the fluxes do have some things in common.   No clean fluxes are designed to leave less residue than Water soluble fluxes.  No clean fluxes are also designed to be benign to the circuit assembly.  There are ingredients contained in the no clean flux residues that could become corrosive or conduct current, which might lead to a failure.  It is commonly assumed that rosins used in the no clean fluxes encapsulate these suspect ingredients so that they cannot harm the circuit assembly.  This is validated through the use of SIR and ECM type tests, but these tests do not always simulate the actual conditions on the circuit assembly.  

I apologize for the very general response.  As Dave Hillman said, if you can give a more specific question, then we can help with more specific answers.  


Best regards,

Tony Lentz

FCT Assembly
Field Application
[log in to unmask]
970-566-0360 Mobile

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Victor Hernandez
Sent: Friday, April 24, 2015 1:31 PM
To: [log in to unmask]
Subject: [TN] LF Solder flux

Fellow TechNetters:

   Are all LF solder fluxes created equal?   I often see m/b with more flux residue, dry-crusty-yellowish, accumulated around the solder joint.  Yet others are almost free of flux residue.   I do see that either solder form a glassy halo around the solder joint at the solder mask surface.   What are the Pros & Cons.   The solder flux residue is more pronounced on Filed return assemblies or those which have been subject to reliability testing, HALT, HASS, S&V & T/C

Victor,


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