The transition to lead-free solder

20 September 2006 Manufacturing / Production Technology, Hardware & Services

The electronics industry has grown up with tin/lead solder. The IEC defines these alloys as Sn60Pb40A, Sn63Pb37A or Sn62Pb36Ag02B. Over four decades the long-term performance of tin/lead alloys has been intensely studied. The IEC and IPC have issued comprehensive documentation, standards and test methodologies that allow manufacturers to ascertain the reliability of their electronics assemblies.

Lead is now banned from electronics assemblies intended for sale in the EU. Legislation of a similar nature is likely to be introduced in Japan, California and China. Both IEC and IPC committees are working hard to try and ensure that revisions to the existing standards are published as quickly as possible, but neither group will have published documents until late 2006. However, both the IEC and IPC are recommending high tin alloys as the best replacements for tin/lead.

Specifically, the IEC states: "The preferred alloy composition should be either Sn96.5Ag3.0Cu0.5 or Sn99.3Cu0.7. An alloy consisting of 3-4% Ag and 0,5-1% Cu with the remainder made up of Sn may also be used instead of Sn96.5Ag3.0Cu0.5. A solder alloy comprising 0,45-0,9% Cu with the remainder made up of Sn may be used instead of Sn99.3Cu0.7."

IPC states: "The solder composition shall be tin (Sn)96.5 silver (Ag)3.0 copper (Cu)0.5 (SAC305) as defined by J-STD-006". The IPC does allow other lead-free solder alloys if agreed between user and vendor.

High tin alloys have not been as well characterised as traditional tin/lead solders. While the IEC and IPC have been rapidly assimilating data on the long-term performance of lead-free alloys it will be some time before comprehensive information is available. Accordingly, both the IEC and IPC are defining thorough testing regimes - with acceptable Gauge R & R - for manufacturers whose products will be used in safety critical applications.

Defining new test methods is critical because the reliability of electronics hinges on the performance of the solder.

Gen3 Systems manufactures the Must System Solderability Tester for wetting balance force measurement and globule testing. The equipment is ideal for both tin/lead and lead-free alloy testing and has been used by the industry for many years. The company has also produced a lead-free bath and globule set and lead-free accessories kit to allow existing Must Solderability Tester owners continuing use of their equipment.

For more information contact Graham Naisbitt, +44 (0)12 5252 1500, [email protected]

Graham Naisbitt is a member of the IEC’s TC91 WG3, the working group that formulates test standards for the assembly industry. He is also Leader of Solderability Testing Standard IEC 60068-2-69, Co-leader of Solderability Testing Standard IEC 60068-2-54, and Member of IPC-J-STD 002 and IPC-J-STD 003.

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