First, welcome to your new job.
Second, IPC-TM-650 2.6.14 is only loosely an �Ionic Contamination (Electromigration) Test�. * Electromigration Test, IPC TM 650 2.6.14, 2.6.14.1 * Ion Chromatography for Ionic Cleanliness, IPC TM 650 2.3.28
Third, IPC-TM-650 is a series of test methods. [You can find them posted on ipc.org ] It is not standard.
Further, your �20 - 80 ug/in^2� sounds like the result of a bulk solvent extract test, like Resistivity of Solvent Extract (ROSE) [Eurolanders call this Solvent Extract Conductivity (SEC)], rather than a Ion Chromatography (IC) Test, which usually talks about contamination level specific contaminants [ie, bromide, chloride, sulfates, etc]. If you know the type on contaminate, it would help focus your search.
Next, possible sources are: * Flux contamination from assembly process (typically a halide ion being present). * Inadequate cleaning after assembly especially under components. * Contamination on component body (handling for example). * Contamination on component leads * Contamination from inside the component that may be leaching out along the leads. * Board fabrication process
As you say, your NC flux could be the source of the problem. If it is, you are applying too much flux. Talk to your supplier for recommendations on proper control. This assumes that we�re talking about wave or hand soldering [SMT flux residues are pretty much well controlled] [In parallel with this, consider using the same IPC-TM-650 2.6.14 to test on inbound bare circuit boards.]
If your hand soldering people are using squirt bottles filled with wave soldering NC flux; shut-down the line, throw all the bottles in the dumpster, and plan your product recall. When using squirt bottles, the raw flux spreads across the board, under components, etc. It�s uncontrolled. The heat of the soldering iron makes it spread faster / further. * When using water washable fluxes, squirting flux �all over the board� is reasonable from a contamination control stand-point [not from an employee health / safety stand-point], because the board is cleaned after hand soldering. * In NC hand soldering, the only portion of this flux that is safe to ship is the small portion that comes to soldering temperature. The remainder is BIG trouble.
Finally, cleaning NC residues is non-trivial. Done improperly, cleaning could increase your contamination levels, if your flux is not meant to be cleaned or you don�t use proper processes and materials. Cleaning water soluble flux residues should be the consideration in your case.
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