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Examine the Oxygen Bomb Test Report Carefully!

Indium Corporation is a big proponant of using the EN14582 oxygen bomb test method for halogen determination.  However, we have seen misleading reports from major test labs when using this test method for solder pastes.  Since the industry is concerned about what remains on the final electronics device when consumers receive it, testing of solder pastes should look at the material that remains on the board after assembly.  Here are some basic facts about solder paste to make my point clearer:

  • Halogens would only be present in the flux portion of solder pastes
  • Pb-Free solder paste is approximately 89% metal and 11% flux (by weight)
  • During the reflow process, approximately 50-60% of the flux volatilizes

Why are these points important?  What I am seeing more and more often is the oxygen bomb report on the solder paste when the flux residue is clearly what is important.  If the report shows that a solder paste has no halogens detected (N/D), it still could be in violation of what the electronics companies want.  Let's assume that in solder paste form, the actual halogen content was 50 ppm of Br (which would often be N/D due to equipment capabilities).   Since the halogen is coming from the flux, that means we have 455 ppm of Br in the flux (50/11%) .  During reflow, let's assume that 60% of the flux volatilizes.  Very little, if any, of the halogen is part of that volatile constituant.  Therefore, if there was 455 ppm of Br before reflow, there will be about 1137 ppm of Br in the flux residue (455/40%).  This is higher than the 1000 ppm allowable maximum recommended by the J-STD-709.

Therefore, it is unacceptable to test solder paste for halogen content.  Even if there is no halogen detected in the solder paste, the flux residue still could be above the acceptable limit.  Be sure the solder paste vendor is at least testing the flux (if not the flux residue).