Requirements for Suitable Lead-Free Alloys

• Relatively Low-cost.
• Relatively non-hazardous
• No Potential Environmental Problems; Ranking in decreasing
  order of safety is: Bi > Zn > In > Sn < Cu > Sb > Ag > Pb.
• Capable of wetting common lead-free component and board finishes.
• Alloys must function with existing flux technologies and desighnations.
• Capable of forming a reliable solder joint, free of oxide inclusions and with minimal solder voids.
• Compatible with relatively low temperature processing.
• Corrosion-resistant and not prone to electrolytic corrosion potential.
• Compatible with copper substrates, immersion gold-over-nickel, and a variety of non-lead substrates, as well as leaded substrates.
• Alloys must be available in bar, wire, performs, spheres and paste forms.
• Metals used in alloying must be available in sufficient quantities.
• Low melting temperatures (< 240°C).
• Good electrical conductivity.
• Good thermal conductivity.
• Easy reparability .
• Adequate strength properties.
• Alloys must be able to be easily recycled.