When testing a solder paste or flux for halogen content, it is still up for debate as to whether or not the sample should be reflowed prior to testing. Those looking to assemble halogen-free electronics are interested in what remains on the board. Therefore, it makes sense to test the residue for halogen content.
Unfortunately, reflowing the material does make the testing more difficult. The reflow profile used could impact the halogen content. Leaving this open for interpretation may allow for the use of an unrealistic profile to make the halogen content of a material appear better or worse. Also, the process of scraping up the residue to prepare for testing allows for contamination.
Indium Corporation would prefer to see a standard developed to be able to perform a halogen test on the raw flux rather than residue. However, this would require some correlation between the raw flux and what would actually appear in the residue. The adjacent figure shows testing of a flux before and after reflow. As expected, after reflow the halogen content appears higher because all of the solvents in the flux have volatilized. In the coming weeks, we will try to correlate the before and after reflow halogen values to the volatility of the flux (through TGA analysis). If a correlation exists, then we will test it on other materials to attempt to validate this correlation.