Legitimate Legislation? From Lead to Halogen

Estimated reading time: 7 minutes

By Steve Dowds, The electronics group of Henkel

Just when the industry thought it had a little breathing room, there are rumblings of yet another push to eliminate certain substances ? namely halogen ? from soldering materials. This article explains the history of halogen, discusses the relevance of recent concerns and proposed bans, and examines the implications of a halogen-free electronics industry.

It seems that the industry barely gets through one major technology shift when another potential legislative effort rears its head. No doubt the pain of lead-free is still fresh on the minds of most electronics industry professionals and there is much evidence to suggest that this discomfort will be felt well into the foreseeable future ? particularly in the pocketbook and, perhaps, even in the environment. Arguably, the effects of the elevated processing requirements of the predominant lead-free tin/silver/copper (Sn/Ag/Cu ? SAC) alloy have been addressed relatively successfully, but this shift has come with some measurable costs in material expense as well as increased energy requirements, not to mention all of the various resources required for a complete technology change.

Just when the industry thought it had a little breathing room, there are rumblings of yet another push to eliminate certain substances ? namely halogen ? from soldering materials. Much like the birth of the lead-free effort, the move to ban halogen from electronic materials has been driven largely by environmental activist organizations such as Greenpeace and the WWF (formerly the World Wildlife Fund). Unfortunately, these groups may erroneously stretch the required bans to include all of a particular class of substances instead of individual harmful substances alone. In the case of halogen-based materials, which are brominated flame retardants (BFRs), environmentalists are seeking to eliminate all BFRs, some of which unquestionably have tremendous benefit (i.e. preventing fires) instead of focusing in on the truly harmful materials in the class, such as polybrominated diphenyl ethers (PBDEs) and polybrominated biphenyls (PBBs). Results from surveys conducted by these groups helped put pressure on the European Union (EU) to eliminate all BFRs rather than just PBDE and PBBs. Therefore, the electronics industry finds itself in a similar situation to that of lead-free: lack of scientific fact supporting the rationale for the ban, but plenty of media attention to help propagate the push for legislation. In fact, several major computer manufacturers ? Dell, HP, Apple ? are already incorporating halogen-free into their latest environmentally friendly initiatives.1 For all intents and purposes, it would appear that the electronics community is rolling a familiar phrase off of its collective tongue: “Like it or not, it’s coming so you’d better be prepared.”

It seems fairly certain that legislation supporting the halogen-free initiative will be implemented. As such, materials manufacturers have been developing compliant materials and material sets to address this latest process shift. But, like lead-free, there will not be a simple “drop in” replacement and technology firms must grasp the implications of halogen-free materials before making any radical supplier or product decisions.

Figure 1. The effect of halogenated material on wetting: the blue line shows a material with the halogen removed.

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A History of Halogen

To fully understand the impact of what halogen-free means, it is important to first discuss the history of the substance and its uses. The term “halogen” comes from the Greek word meaning “salt producer;” it describes the elements bromine, chlorine, fluorine, iodine, and astatine. Commercial applications for bromine compounds include pesticides and fumigants, and pharmaceuticals where brominated substances are essential ingredients of many drugs including antihistamines and analgesics. By far the most important application is BFRs.

For the electronics industry specifically, bromine and chlorine are of particular interest. In its elemental form, bromine is a volatile liquid at room temperature; however, bromine is never found naturally occurring in its elemental form, only in compounds with other substances. Examples include bromide salts or organo-bromine compounds, produced by many marine organisms. Seawater contains bromine at the level of about 65 parts per million (ppm); higher concentrations (2,500 to 10,000 ppm) exist in inland seas.

Halogenated materials are found in flame retardants in PCBs, with PBBs and PBDEs presenting the greatest toxicity concerns. They therefore were banned by the EU RoHS Directive. Now, there is an attempt to restrict the use of all halogenated materials in electronics because of the belief that brominated materials, if incinerated, can form highly toxic dioxins. This goes beyond the initial RoHS restriction on PBBs and PBDEs.

Are All BFRs Bad?

In 2003, the WWF published a U.K.-wide biomonitoring study which looked for 78 chemicals ? including flame retardants ? in people’s blood. Several highly alarming statements resulted, such as, “Every person is contaminated by?PBDEs,” and, “We are being contaminated daily by ?unregulated’ chemicals of unknown toxicity, such as the deca-BDE flame retardant.”2

Toxicologists panned the results. Professors Alan Boobis and John Henry of Imperial College called the campaign “irresponsible, hysterical scaremongering,” stating that “you find flame retardant traces because we have them in our homes. That’s why fire deaths have plunged. These chemicals are monuments to mankind’s progress.” Professor David Coggon of Southampton University said, “People are being pressed to make decisions on misleading information.” Professor Ken Donaldson of Edinburgh University concurred, commenting that “groups are deliberately confusing risks with hazards.”3

Improper incineration of any substance can lead to toxic gas formation, so outlawing BFRs ? even if all of them were harmful ? would not achieve the desired result of reduced environmental dioxins. Experts found that increasing the content of BFRs in the waste gave no significant increase in the emissions of chlorinated dioxins or either brominated and/or chlorinated/brominated dioxins. The emission level is highest for chlorinated dioxins, lower for chlorinated/brominated dioxins, and lowest for brominated dioxins. Finally, emission measurement results indicate that the incineration efficiency and the operating conditions of the flue gas treatment systems are of greater importance to the resulting emission levels for dioxins than that of the bromine content level.4

While PBBs and PBDEs are known to be potential endocrine-disrupting chemicals and rightfully are banned, most electronics products actually use deca-BDE and/or deca-brominated diphenyl ether/tetrabromobisphenol-A (TBBPA). On April 1, 2008, the European Court of Justice banned the use of deca-BDE. On April 9, this decision was accepted by the European Commission and the ban took effect July 1. However, on May 29, 2008, the commission published the results of its own risk assessment of deca-BDE, a study that began in 2004. This concluded that there was no risk in using deca-BDE, which leaves the EU in the astonishing position of banning the use of a chemical that its own risk assessment concluded was not a hazard.5 Furthermore, a decade-old World Health Organization (WHO) study comprehensively assessed the human and environmental impact of TBBPA, finding that it has little potential for bio-accumulation and that the human health risk associated with TBBPA is considered to be insignificant.6

Figure 2. A properly formulated halogen-free material with good wetting performance.

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Halogen-free’s Impact on Soldering

The average PCB contains about 1?2% TBBPA content. A typical flux medium may contain as much as 1% brominated activator by weight (varying by manufacturer and by formulation) and these brominated materials confer significant advantages in terms of solderability and stability. Removing these substances can compromise certain aspects of the product performance, such as wetting (Figure 1). Usually, the requirements of solderability, stability, and reliability are conflicting and need to be balanced. For example, to achieve a good solder joint when joining poor surfaces, more activator may be required. This can reduce shelf life; the high level of activator will react with the powder in the solder paste at room temperature and cause the viscosity to increase, making it impossible to print. Equally, high levels of activator can compromise the surface insulation resistance and lead to electrical failures. BFRs offer an excellent way of squaring this circle; because the bromine is covalently bonded, it is not available for fluxing reactions at room temperature ? it only becomes available at high temperature. If the BFR material is removed, conventional activator chemistries must be used. These materials likely will not offer this same benefit.

When one breaks down the actual BFR content in current solder paste formulations, it is curious as to why these materials are included in the proposed legislation. Assuming that the solder paste is 90% metal by weight, once metal is added to the solder paste, the portion of brominated material is reduced to 0.1%. A typical PCB may use 0.5 g of solder paste, meaning only 0.05 g of flux medium. Consider that possibly 50% of this will be lost through evaporation during the reflow process leaving only 0.25 g of flux residue (of which 1% was brominated to begin with).

Perhaps seeking to abolish the use of all bromine-containing materials from fluxes and solder pastes is misguided. The industry is preparing to spend a considerable amount of money and resources to replace materials with a known benefit (reduction of deaths in fires) to assuage fears of a potential risk. Aside from PCBs, epoxy resin chemicals all contain chlorine. Eliminating chlorine incurs considerable additional cost as purer resins require additional processing, for negligible environmental benefit.

Accepting the Inevitable: Considerations for Halogen-free

It appears that the industry is going halogen-free as a sensible commercial decision. Recognizing this, materials manufacturers are developing compliant solder products that offer the performance required by advanced technology firms. Total value chain materials suppliers are offering complete halogen-free material sets.

Understanding exactly what “halogen-free” means is of critical importance for any company considering implementation. As Laura Turbini, Ph.D., so aptly pointed out in a recent commentary,7 the term “halogen-free” is a bit of a misnomer, as low levels of halogen will be allowed under current proposed legislative guidelines. According to various industry standards, the accepted levels range from up to 900 ppm bromine, 900 ppm chlorine, and maximum total halogens of 1500 ppm.8

Figures 3A and B. The chemistry balance of halogen-free materials must be tightly controlled. Both of these images are of halogen-free solder pastes: one (A) shows poor linear wetting performance, while the other (B) shows good linear wetting performance.

To prove halogen is not present in PCB assembly materials, manufacturers must conduct a combustion test followed by ion chromatography. This causes decomposition of the brominated activator materials and the material which is covalently bonded at room temperature (and thus not detectable by the current standard test methods) is available and measurable. If no halogen is found with this test, the assembly will pass the relevant industry standards and, for the time being, Greenpeace and the WWF should be satisfied.

Making the decision to go halogen-free requires research, particularly when selecting a materials partner. Many materials are being marketed as halogen-free, but in practice they will not qualify, as BFRs are still deliberately added to the formulation. Other materials suppliers are developing halogen-free flux chemistries with no deliberately added halogen. The R&D may be more time-consuming when following the proper route to halogen-free, but the end result could prove to be more beneficial as new, truly halogen-free solder pastes have shown excellent reflow capability in early lab testing (Figure 2). Without extensive materials science R&D, halogen-free materials can have disastrous effects on the soldering process (Figure 3).

Conclusion

Just as with the early days of lead-free, there is still much debate to be had and even more testing required before there is a final word on halogen-free implementation. However, it appears that the industry is preparing itself for a halogen-free existence. Therefore, it is imperative that manufacturers actively engage in researching and understanding their own requirements, the potential challenges, and the capabilities of their materials suppliers. The industry has learned a lot from the lead-free experience. Let’s hope those lessons provide a good foundation for making wise decisions about halogen-free. SMT

REFERENCES:

1. 1.,7. Turbini, L., “Halogen: The Latest Green Initiative,” SMT Online, July 2008, www.smtonline.com.
2. 2.“Contamination: The Results of WWF’s Biomonitoring Survey,” November 2003.
3. 3.McKie, R. “Poison Experts Attack ?Hysteria’ Over Chemicals”, Observer, September 18, 2005.
4. 4.Borgnes, D. and Rikheim, B., “Decomposition of BFRs and Emission of Dioxins from Co-incineration of MSW and Electrical and Electronic Plastics Waste”, Organohalogen Compounds, Volume 66, 2004.
5. 5.“EU20402 EN EU Risk Assessment Report ? Bis(pentabromodiphenyl)ether, Vol 17.”
6. 6.World Health Organization International Program on Chemical Safety (IPCS): Environmental Health Criteria 172: Tetrabromobisphenol A & derivatives, 1995.
7. 8.Standards: IEC 61249-2-21, JPCA-ES-01-1999, IPC 4101B.

Steve Dowds, global product manager, Multicore soldering materials, the electronics group of Henkel, may be contacted at +44 (0) 1442 278 053; steve.dowds@uk.henkel.com.