Halogen-free is not for free!

That was a significant conclusion of the European Institute of Printed Circuits technology seminar held in Birmingham, UK, on 6th September 2006.

In the context of a trend for OEMs to specify halogen-free materials for new electronic products, often in conjunction with their RoHS compliance programmes, without necessarily understanding the impact on bare board manufacturing processes or costs, the seminar explored some of the legislative aspects and technology issues encountered in fabricating PCBs from halogen-free laminates.

Hans Wendschlag, Hewlett Packard's environmental strategist, spoke from the point of view of a global OEM, for whom an enormous challenge was to comply with the often conflicting requirements of different product standardisation bodies and labelling conventions worldwide. An ironic example was that, in Europe, the WEEE Directive appeared to be interpreted differently by every member country. And many more directives, for example the Integrated Product Policy Directive and the EcoDesign of Energy-using Products Directive would be progressively integrated into CE marking regulations. An important commercial consideration for the OEM was "Green Public Procurement" - public authorities, whose spend in Europe, for example, represents 16% of the region's GDP, using environmental considerations to justify their purchases and heavily influencing the marketplace as a consequence. Hewlett Packard had so far produced over 1000 Eco self-declarations pertaining to materials and flame retardants. As corporate policy, they had eliminated the use of PBBs, PBOs and PBDEs, and avoided the use of PVC wherever possible.

The annual consumption of flame retardants in Europe is estimated at 465,000 tonnes. Veronique Steukers from the European Brominated Flame Retardant Industry Panel reported work that had been done to demonstrate that there are no hazards, either to human health or to the environment, resulting from the incorporation of tetra-bromo-bisphenol-A (TBBPA) into FR4 laminating resins. And, significantly, there was no legislation in Europe against any of the flame retardants currently used in PCBs, although the new REACH (Registration, Evaluation and Authorisation and Restriction of Chemicals) regulations, expected to come into force in spring 2007, would make manufacturers and importers of materials responsible, at their own expense, for submitting data on physical, chemical and toxicological properties of all materials, not just flame retardants.

With specific reference to flame retardant laminates, Dr Adrian Beard of Clariant described the advantages and disadvantages, both technical and financial, of various examples. Flame retardancy could be achieved either by the use of additives such as aluminium trihydrate, aryl phosphates or proprietary phosphinates in traditional resin systems, or by developing new resin and hardener chemistries based on materials such as triazine-modified novalacs or dihydro-oxa-phosphaphenanthrene oxides. Several halogen-free laminates were commercially available, mainly originating in the Far East, and although some had improved physical properties as compared with TBBPA-FR4, these benefits were generally offset by increased cost.

Paul Ranken of Albemarle Corporation re-emphasised the fact that no evidence existed of any toxicological or environmental hazard consequent upon the incorporation of TBBPA into FR4 resins with the quote: "All halogen-containing carbon-based bodies (including humans) will form some dioxins upon incineration, but any dioxins formed by combustion of TBBPA-containing materials are not at levels of concern to any regulatory authority". Having reviewed the relative costs of several alternative routes to achieving UL94V-0 flame retardancy, all of which were significantly more expensive than baseline FR4, he concluded that any meaningful replacement system must not only out-perform TBBPA on cost, toxicological and environmental considerations, but also show significant performance-in-use benefits.

Laminate supplier Geoff Layhe of Lamar described the properties of some commercially-available materials which had processing characteristic similar to those of standard FR4. The latest halogen-free laminates had been shown to give better thermal conductivity, better comparative tracking index, better conductive anodic filament resistance and better through-hole reliability than traditional dicy-cured FR4. European usage was increasing, currently around 50,000 sq M per month of laminate and 140,000 of pre-preg, although the main drive was coming from Japan and South-East Asia. Lead-free solder compatibility was a potential technical advantage, but the real question remained as to whether environmental or marketing considerations were the real issue.

Although the processing characteristics of halogen-free laminates had been stated as nominally equivalent to those of FR4, a note of caution came from Steve Price of Atotech who described the huge characterisation programmes which suppliers of desmear and metallisation chemistries were having to undertake in order to adapt and optimise their process parameters to suit individual examples. In general, these materials were more chemically resistant than FR4, and successful processing demanded tighter controls, with close cooperation between supplier and PCB fabricator.

In his summing-up of the presentations and the interactive discussion which they had provoked, EIPC Technical Director Michael Weinhold commented "You may get more market share because it's green, but you certainly won't get more margin!" And, as ever, the PCB fabricator would be expected to carry the burden of additional expenditure unless EIPC and its members could persuade OEM and EMS companies to contribute a fair share of these costs by making them aware that the marketing-driven need for halogen-free PCBs resulted in a more expensive materials and manufacturing processes, and educating their engineers that although the increased thermal resistance of some halogen-free PCBs might facilitate lead-free soldering, the added value did not come for free.

He also reminded the delegates that, although many new "green" proposals originate in Japan, and subsequently become adopted as IEC standards which European standards then have to follow, so far as the International Electrotechnical Commission is concerned, Japan has only one vote whereas the Europe Union, with 25 member states, was in a position to out-vote proposals considered not in the best interests of the European electronics industry.