Lead-free solder toxicity

KEMI (2000). Non-toxic Environment. See www.kemi.se Aerojet Propulsion Division (1991) speaking at a conference on Alternatives to I ncinerable Waste Streams, California Richards, B (2002). Lead-free Soldering. National Physical Labs. See www.npl.co.uk/npl/ei/news/epparticle. html... 

Over the last decade, the industry has studied a wide range of alloys to replace the tin-lead alloy. The alloy selection has been based on the following considerations (Ref 12-15) toxicity, physical properties (melting temperature, surface tension and wettability, thermal and electrical conductivity), mechaiucal properties, mi-crostructural characteristics, electrochemical properties (corrosion, oxidation and dross formation, and compatibility with no-clean fluxes), manufacturability, cost, and availability. Yet another important consideration for selecting the lead-free solder alloy for commercial use is whether or not the alloy may be covered by any patents. Lead-free alloy selection, as weU as associated patent issues, have been described in detail in toe literature in Ref 16-20. 

Lead-Free Solder Alloys. Because of the toxicity of lead and the concern that the lead in electronic products may end up in landfills, and ultimately in the water supply, the electronic industry is exploring alternative solder alloys that do not contain lead. These alternative solder alloys are typically composed of tin (Sn), with one, two, or three additives such as copper (Cu), silver (Ag), bismuth (Bi), antimony (Sb), zinc (Zn), or indium (In). Typical tin lead-free candidate solder alloys include Sn-Cu, Sn-Ag, Sn-Ag-Cu, Sn-Ag-Cu-Sb, Sn-In, and Sn-Cu-Bi-Sb. Some of these are more suitable for wave solder... 

Directive 2002/95/EC Restriction of the Use of Certain Hazardous Substances in Electrical and Electronic Equipment (RoHS) requires the components to be free of toxic substances, with only a few exceptions. Only lead-free solder can be used. Lead-free solders generally have higher melting points, so soldering operations have to be hotter and the components correspondingly temperature-resistant. 

The study of the relative toxicity of various metal elements used in electronics is important as the industry evaluates new solder alloys and new component materials. The Surface Mount Council reported various elements comprising lead-free solder alternatives [27] (Table 7). Based on this and other data cited in the report, toxicity ranking assigned to the common lead-free solders alloying elements are as follows ... 

Smith, Edwin B. III. Environmental Impacts and Toxicity of Lead Free Solders, Including Japanese and European Union Regulations,. Proc. IPC Works 99 Minneapolis, MN, Oct. 1999. 

The RoHS Directive was a major catalyst for research and adoption of lead-free solutions in electronic equipment. Alternatives to lead in soldering range from tin (Sn), silver (Ag) and copper (Cu) to bismuth (Bi) and zinc (Zn). These heavy metals do not have the same toxicity and bioaccumulation potential of lead (Pb). ... 

The classical electronics solder alloy (Sn + 37 wt% Pb) contains the inhalation-toxic element lead and is being replaced in electronics for health reasons. A Pb-free solder is Sn-3.5wt% Ag indium and bismuth alloys are other eutectic-forming alloying additives to Sn. The classical brazing alloy is at the Cu-Ag eutectic (Ag-F 28.1 w% Cu) and is well suited for mechanically strong contacts with Cu and its alloys. 

---