Ion Chromatography (J-STD-004; TM-650 #2.3.28):
This is a quantitative test that can identify the total quantity of halides present in a flux. Based on
the retention time in the ion exchange column, a chromatogram is developed and peaks are identified
as various ions based on previously developed standards. This test method allows you to quantify
how much halides are present and which particular halide. The challenge with ion chromatography
is that it only identifies the ionic species and the covalently bonded halides are not detected. In addition,
there are chemicals that have similar retention times to Cl- and Br- which can result in non-halides
being misidentified as a halide. There is a growing practice of running ion chromatography on reflowed
flux residue. This technique can probably more accurately detect halides in the flux because halides
won't volatilize and some of the covalent bonds may have been broken. However, unless all of the
covalent bonds are broken, the testing of the flux residue will still under assess the amount of halides present.
Oxygen Bomb Combustion Followed by Ion Chromatography (EN 14582):(Combustion flask)
This is quantitative test method that is recommended by Indium Corporation and is growing in
popularity throughout the electronics industry. This test method involves subjecting a sample of
flux to an oxygen bomb Combustion in which the all of the organic material is burnt off at very high
temperatures. The remaining ash consists of the halogens and other inorganic materials. That ash
is the run through ion chromatography in which a true reading of halide content can be determined.
Any covalently bonded halides have those bonds broken through the oxygen bomb process. Since
most halogen restrictions are based on the finished circuit board. Assembly, there has been discussion
on whether the oxygen bomb & IC test should be run on the flux residue rather than raw flux. This
presents a challenge as the scraping of flux residue can potentially remove some of the circuit board.
In addition there may be some difference between the residue near the solder joint and residue that has
spread a long distance from the joint (where the residue is scraped can make a difference). Both of
these challenges make the testing of the residue less than ideal.