RoHS (Restriction of Hazardous Substances Directive) is the restriction of the use of certain hazardous substances in electrical and electronic equipment and was adopted in February 2003 by the European Union.

RoHS is often referred to as the lead-free directive, but RoHS restricts the use of six hazardous materials in the manufacture of various types of electronic and electrical equipment. It is closely linked with the Waste Electrical and Electronic Equipment Directive (WEEE), which sets collection, recycling and recovery targets for electrical goods.

Restricted materials

  • Lead (Pb)
  • Hexavalent chromium (Cr 6+)
  • Mercury (Hg)
  • Polybrominated biphenyls (PBB)
  • Cadmium (Cd)
  • Polybrominated diphenyl ether (PBDE)

PFC’s flex circuits are RoHS compliant as long as the surface finish is compliant.

Standard, compliant surface finishes include:

  • ENIG – Immersion gold over electroless nickel
  • Immersion tin
  • Electroplated soft or hard gold over electroplated nickel
  • OSP – Organic Solderability Preservative
  • Immersion silver

RoHS lead – free assembly

The other area where flex circuits may be affected by RoHS is the assembly and solder process. PFC provides both lead and lead-free assembly of flex circuits. PFC urges customers to take care in selection of RoHS solders as some formulations are harder (requiring higher melting temperatures) with less ductility, increasing the likelihood of cracks instead of plastic deformation, which is typical for lead-containing solders.

Higher temperatures can cause via reliability issues, and solder cracking. Cracks can occur due to thermal or mechanical forces acting on components or the flex circuit, the former being more common during manufacturing and the latter in the field.

For SMT assembly, lead-free solder present challenges especially with the varying sizes of components on a single circuit. Care must be taken to choose solder paste, optimum stencil aperture, reflow oven time and temperature. PFC has been providing RoHS assemblies since the inception of RoHS (2006).

Ask your PFC technical resource for lead free assembly recommendations.