Indium Blog

The Difference Between Halogen and Halides in SMT Solder Pastes

Phil Zarrow: This video is for anybody considering halogen-free solder paste or flux. It includes the differences between halides and halogens.
Brook, I remember halide-free fluxes in the days of tin-lead solder paste. What is the difference between halide- and halogen-free?
Brook Sandy: With halide-free fluxes, the important thing was to not have ionic halogens, like chlorine, bromine, iodine, or fluorine, in the raw flux; whereas halogen-free fluxes, you're concerned about chlorine or bromine being present in the flux residues after reflow.
Phil Zarrow: What's the source of concern?
Brook Sandy: With halides, the source of concern is ionic elements being still mobile on your assembly, which could lead to electro-chemical migration; whereas halogens are a concern in the final assembly, when the printed circuit board is being recycled, you don't want to release halogens into the atmosphere.
Phil Zarrow: What are the current industry regulations for halogen-free?
Brook Sandy: There's an optional test for oxygen bomb testing, in J-Standard 4, which would require 1000 PPMs of bromine, or 1000 PPMs of chlorine, in this testing, for low-halogen.
Phil Zarrow: Where can I find more information on halogen-free?
Brook Sandy: Visit our halogen-free page at, or you can email me directly at
Phil Zarrow: Brook, thank you very much.