Lead-Free

The Implications of the European Union Directives Numbers 2002/96/EC and 2002/95/EC are being felt by printed circuit manufacturers throughout the World.

 The objective of Directive Number 2002/96/EC on Waste Electrical and Electronic Equipment (WEEE) states:- : "The purpose of this directive is, as a first priority, the prevention of waste electrical and electronic equipment (WEEE), and in addition, the reuse, recycling and other forms of recovery of such wastes so as to reduce the disposal of waste. It also seeks to improve the environmental performance of all operators involved in the life cycle of electrical and electronic equipment, e.g. producers, distributors and consumers and in particular those operators directly involved in the treatment of waste electrical and electronic equipment."

 The objective of Directive Number 2002/95/EC on the Reduction of the Use of Certain Hazardous Substances in Electrical and Electronic Equipment. (RoHS) states:- "The purpose of this directive is to approximate the laws of the Member States on the restriction of the use of hazardous substances in electrical and electronic equipment and to contribute to the protection of human health and the environmentally sound recovery and disposal of waste electrical and electronic equipment"

The WEEE directive is concerned with the reuse, recycling and disposal of waste electrical and electronic equipment, and the RoHS directive is concerned with removing certain hazardous substances from electrical and electronic equipment in order to make the reuse, recycling and disposal safer and less hazardous to the environment.

From July 2006 new electrical and electronic equipment (with some exemptions) must not contain lead, mercury, cadmium, hexavalent chromium, polybromonated biphenyls (PBB) or polybrominated diphenyl ethers (PBDE).

Generally, copper clad laminates do not contain any of the restricted substances, (a small amount of chromium is used to passivate the copper surface but this does not get as far as the finished circuit board).

 The flame retardant used in "standard" FR4 laminate is tetrabromobisphenol-A (TBBA), at present the use of TBBA is not restricted by European Legislation. However there is a push from equipment manufacturers to remove halogens from their products. This has led to an increase in the use of halogen free laminates especially in Japan, and this trend will probably continue in the future. Halogen-Free laminates such as R1566 from Matsushita are available now.

 All common copper clad laminates are lead-free; the term "lead-free laminate" refers to the laminate's suitability for lead-free processing.

 It is the restriction on the use of lead which will, potentially, have the biggest effect on circuit board manufacturers and assemblers. Typically the solder used for circuit board connections contains 37%-40% lead.  Much work has been carried out on lead-free "solder" alloys and the common issue of the replacement alloys is that they have a higher melting point than 63/37 solder. the soldering temperature can be 40C higher than 63/37 solder   This means that Hot Air Solder Levelling needs to be carried out at higher temperatures or an alternative finish must be used, such as immersion tin, silver, OSP or ENIG.

The higher soldering temperatures needed for lead-free soldering put extra stress on the circuit board laminate especially if more than one soldering operation is being carried out.

At present there is no standard to which laminate can be qualified to show suitability for lead-free soldering, and it is possible that for some applications "standard" FR4 may be adequate, although higher soldering temperatures, coupled with possible thermal cycling during use, make it more and more unlikely.

The important characteristics to take into account when choosing a laminate for lead-free soldering are:- the decomposition temperature (Td) and the time to delaminate at 260șC (T₂₆₀). Standard FR4 has a Td of around 300șC and a T₂₆₀ of about 4 minutes. High Tg  does not necessarily mean that the laminate is suitable for lead-free soldering since some high Tg FR4s have the same Td and T₂₆₀ as "standard" Tg FR4s.

Newer laminates, which are still classified as FR4, but which have better thermal characteristics than "standard" FR4 are being introduced for Lead-Free soldering. These laminates typically have a Td of  330șC and a T₂₆₀ of greater than 60 minutes. These laminates can be processed in a similar manner to "standard" laminate but are able to withstand higher process temperatures and are better suited to use in situations where the end product may operate at higher temperatures or may be subject to thermal cycling.

Examples of these products are R1566 from Matsushita and & N4000-11 from Nelco.

Further information concerning WEEE and RoHS can be found at the following links:-

http://www.environment-agency.gov.uk/netregs/legislation/

http://www.npl.co.uk/ei/research/leadfree.html

http://www.npl.co.uk/ei/news/faqs.html

http://www.envirowise.gov.uk