May/June, 2012
www.us-tech.com
Page 59 Are Your Materials Really Halogen-Free? By Mark Currie, Ph.D., Henkel Electronic Materials LLC T
hough there is no official, gov- ernment-mandated require- ment forcing the production of
halogen-free products and, therefore, the use of halogen-free materials, the electronics industry has arguably moved in that direction. This indus- try-sponsored effort is being driven primarily by increasingly environ- mentally-conscious customers, pres- sure from non-governmental envi- ronmental organizations and the desire by suppliers to be proactive. But, in order to understand the halo- gen-free movement, one must fully comprehend the reason behind the push as well as the differences between halogens and halides. In their form as contained in electronics devices, halogens do not cause harm to humans or to the environment. The concern regarding halogenated materials has arisen because of the harmful byproducts that can be released into the environment at the end of a product’s life during the incineration process.
Halogen-free and halide- free are not one and the same, in spite of some pop- ular misconceptions among industry professionals.
Certain halogen-based materi-
als, also known as brominated flame retardants (BFRs), present more of a concern than others and generally include polybrominated diphenyl ethers (PBDEs) and polybrominated biphenyls (PBBs). Incineration of these materials releases dioxins into the atmosphere and these byprod- ucts can be harmful to humans. In fact, dioxins have been shown to be present in increasing levels in soil, ground water and people. Even though the majority of electronics products contain no PBDE or PBB, fear of having the term “halogen” associated with any electronics mate- rials is pushing the industry toward a halogen-free existence.
Halide vs. Halogen Surprisingly, many electronics
professionals incorrectly answer this question in the affirmative. However, the answer is most certainly “no”: just because a material is halide-free doesn’t mean it is also halogen-free.
Here are the differences for Halides: l
Ionic and have a charge (example Cl-, Br-, and F-).
l l l
Added to solder paste to improve activity, encourage cleaning.
Generally hydroscopic and can cause stability challenges.
No-clean fluxes normally encap- sulate remaining halide constituents post reflow in the rosin to ensure post assembly reliability.
Here are the differences for Halogens: l
l l
Primary source in electronics assemblies is in BFRs in laminates.
available for fluxing activity at room temperature but only at high temperature.
, Br2 , and F2 ); not
Covalently bonded group VIIA element without a net ionic charge (example Cl2
Certain halogens — PBBs and PBDEs — present potential toxicity problems when inciner-
See us at SMT Hybrid Pkg. Booth 7-531 l Used in solder paste to enhance a ted (causing dioxins).
activity without impact to reliability.
It is also important to under-
Table 1. Classifications, test procedures and standards for halide-free and halogen-free.
stand the different reactions of halides and halogen materials both at room temperature and at elevated temperatures. Ionic halide bonds are typically easily broken, which allows free halide to react with moisture and cause corrosion at room temper- atures. Conversely, covalently bond- ed halides are much more stable at room temperature and the bonds are not easily broken. At elevated tem- peratures — such as those consistent with soldering — the covalent bonds are broken and the halide can react Continued on page 61
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