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Halogen-Free Solder Paste - Part 3

It seems that the topic of Halogen-Free Solder Paste has grown by another leap and bound. The big confusion is what are the definitions of Halogen-Free Solder Paste. I mean, who decides what techniques to use for the determination of Halogen-Free Solder Paste. The different testing and procedures come from many sources, including the IPC and individual Original Equipment Manufacturers (OEM's). So, lets take a few minutes and discuss not the techniques used for testing Halogen-Free, but the procedures and reporting specifications. For procedure references, please check original post, Halogen-Free Solder Paste. The first specification that comes my mind, is the IPC's "J-Standards" or J-STD. The section of the J-STD that covers the halogen and halide specifications is J-STD-004. The current revision "a" states that the halogen and halide content is tested on the reflowed solder paste, by Ion Chromatography. Here is the IPC's test method IPC-TM-650 2.3.28.1. As we have discussed in the past, Ion Chromatography is good for testing ionic halides, but may miss the covalent halogens, and of course any volatiles that contain halogens and halides. It is by this method, that some solder paste that are indeed halogen containing, can still advertise themselves as halide-free per J-STD-004. I'm not going into details about the procedure, but it involves a molten solder pot, a Petri dish, and a plastic bag. Sound very scientific to you? Me neither; more like a 9th grade science fair project. By the way, the IPC's definition of Halide-Free is <0.05% (500ppm) total halides. No mention of halogen-free. Another specification that is preferred by some OEM's states that a test board be printed with solder paste, then reflowed and tested by Ion Chromatography. At least this is board-level testing, but the definition of halogen-free versus halide-free remains, as well as their definition of halide-free, <0.09% (900ppm). I have personally tested pastes to this specification, and on one test, knowing that there is >0.5% (5000ppm) total halogens in the sample of the raw flux, have it come back on this test as <0.001% (10ppm). Knowing this is not bad, if only based on the fact that the halide-containing activators may have burned away. Lets get into the big-ticket topic; "no intentionally added halogens". One of the only test methods of determining total halogen content is Parr Oxygen Bomb, then ion chromatography of the ash, on the raw solder paste or flux. This will give you both the halogen and halide content of the flux vehicle. It is no secret that some OEM's looking into truly halogen-free solder pastes, after testing that has showed that their "halide-free" per J-STD-004) pastes that they are using now, is failing due to corrosion or dendritic growth. The statement "no intentionally added halogens" sums it all up, where in reality, only the naturally halogen-containing compounds would be detected, such as the rosin. Even on the post-reflow flux residue, ion chromatography may still miss the covalently bonded halogens, but not oxygen bomb testing. More information may be found at our Online Help: Indium Knowledge Base.