My colleagues at Indium Corp tell me that some major companies are now starting to specify maximum halogen levels in solder paste flux residues after reflow.
The following are some discussion points regarding recent specs from customers concerning halogen levels in flux residues:"The emphasis is on all kinds of bromine and chlorine, including organic, inorganic, covalent bond and non-covalent bond. Acceptable levels are less than: Bromine ˜ 900ppm Chlorine ˜ 900ppm Total Bromine+Chlorine ˜ 1500ppm Also noted in the specification, it covers the flux residue that is left on the board. But did not specify exactly which test method, only mentioned IC is acceptable and NOT XRF."
I think the test method will need work as IC (ion chromatography) can't detect covalently bonded halides. See Tim Jensen's discussion on halide analysis. I expect these types of specs to be refined over time.
Many think "halides" in fluxes will be "the issue" in 2008. Stay tuned. I will try to keep you updated on this topic.
The image above is a halide-free solder paste from Indium Corp.