RoHS Directive switches materials

This article looks at the implications of the RoHS Directive on the switch industry.

RoHS, the European Parliament directive 2002/95/EC titled Directive on the Restriction of the Use of Certain Hazardous Substances in Electrical and Electronic Equipment, provides for the elimination of specific substances used in electrical and electronic equipment that are deemed to pose health and environment risks.

The directive has restricted the use of six materials; lead (Pb), mercury (Hg), cadmium (Cd), hexavalent chromium (Cr VI), polybrominated biphenals (PBB) and polybrominated diphenylethers (PBDE).

As of 1st July 2006, these materials will not be permitted in electrical and electronic equipment sold in the European Community.

Some of the soon-to-be-banned materials listed in the RoHS Directive have minimal effect on switch products.

Hexavalent chromium (Cr VI) is rarely used in the chrome plating process for switch components.

Polybrominated biphenals (PBB) and polybrominated diphenylethers (PBDE), once used as heat stabilisers in plastic components have been replaced in most cases.

Mercury is still used in tilt switches, but this application is quickly being phased out.

This leaves two substances, used extensively by the switch industry over the past six decades, cadmium and lead.

Cadmium was used for years as a colour (red) pigment in plastic components.

This practice began being phased out in the mid 1990s, and most switch manufacturers have completely phased out this use of cadmium.

Cadmium remains the material of choice for high current electrical contacts in switches and relays in the form of silver cadmium oxide (AgCdO).

Silver-cad-oxide (as its known in the industry) exhibits high electrical and thermal conductivity, excellent resistance to erosion and resists contact welding under arcing conditions.

AgCdO contacts are typically produced through the mixing of silver and cadmium oxide using powder metallurgy technology.

The high conductivity and low contact resistance is actually close to that of silver (silver has the highest electrical and thermal conductivity of any metal) yet it exhibits superior erosion and welding resistance compared with silver, due to the inherent arc-quenching characteristics of cadmium oxide.

Silver-cad-oxide contact materials contain up to 15% cadmium oxide.

Unfortunately, alternatives to silver-cad-oxide do not provide the same benefits.

One material being considered as a replacement by many switch companies including Apem, is silver tin oxide (AgSnO).

Silver tin oxide contacts are harder than AgCdO and provide superior welding resistance but unfortunately provide lower electrical conductivity performance.

An exemption from the RoHS Directive was granted for the use of cadmium and its compounds in electrical contacts on 21st October 2005 (via an amendment to the Annex to Directive 2002/95/EC).

Apem has begun research on alternatives, but continues to offer silver-cad-oxide contacts for high-inrush-current applications of its 2600 series industrial rocker switches.

The second material used extensively by the switch industry over the past 60 years, and the material most people relate to the RoHS Directive, is lead, or more specifically tin/lead solder and tin/lead plating.

Tin/lead has generally been used on all switch surface mount terminations and some through-hole terminals and mounting brackets.

The RoHS Directive has forced PCB and component manufacturers towards "lead free" processing, producing two challenges for the switch industry; the elimination of lead and the modification of product designs to ensure switches can withstand the higher temperatures associated with new lead-free solder processing.

Switch manufacturers have been slowly eliminating tin/lead plating over the past 12 to 18 months in anticipation of the pending deadline and have been attempting to convert plastic components to higher performance alternatives.

Apem has developed alternatives to tin/lead, offering silver, gold and matte tin plating options on its 125 families of switch products.

Apem chose matte tin over bright tin for its reduced risk of tin whiskering.

Apem had a few key advantages in the race towards RoHS compliance.

Apem is vertically integrated and its lean manufacturing allowed for minimum nonRoHS component inventory when the transition began.

And vertical integration meant a close proximity to raw material suppliers providing for instant feedback when RoHS materials became available.

Another advantage, Apem is recognised as one of the premier switch brands in Europe.

Apem sells over 30 million switches each year into the EU marketplace.

Apem's connection to the EU forced it to begin work towards RoHS compliance in the early days, before most manufacturers contemplated the July 2006 deadline.

Apem converted to high temperature materials over five years ago.

Most power toggles and rockers are made from high-temperature thermoset plastics, capable of withstanding extreme solder temperatures.

Miniature switch products, available in both through-hole and surface mount configurations were converted to high-performance thermoplastics in 2001, in anticipation of hybrid PCBs and higher solder temperatures.

Many of Apem switch products are designed for panel mounting rather than PCB mounting.

These products were originally designed with gold or silver plated contacts and met the requirements of the RoHS Directive from the start.

Almost 80% of Apem switches have always been RoHS compliant.

Today, all of Apem's switch production lines are producing RoHS compliant products and 95% of Apem's finished goods inventory is RoHS compliant.

If a customer requests a RoHS compliant switch Apem and its distribution partners can deliver it, in many cases from stock.

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