Lead free soldering electronic interconnect: Current status and future developments

There is world-wide concern about the potential ecological impacts of lead-based solders, present in old electronic equipment buried in landfill sites. This paper reports the results of over nine years R and D at Nortel Networks on identification, evaluation and deployment of lead-free solders for printed circuit board assembly. This work has resulted in the production of the world´s first virtually lead-free telephone-the Nortel Meridian 8009-by using a lead-free, tin-copper solder. To date, this telephone has passed a battery of functional tests and logged over 3.5 years of fault-free operation in normal usage. Other applications include mobile telephones and backplanes for PABXs. The technical and economic criteria used to select the tin-copper alloy are described, together with progress in producing compatible HASL tin-copper PCB finishes and tin-copper plated finishes on components. Reliability aspects of this alloy are also discussed. The challenges remaining to implement this lead-free technology into more complex telecommunications components including array packages and chip scale semiconductors via the jetting of lead free alloy spheres are discussed. The replacement of high lead, high melting point circa. 280°C solder alloys is another topic that will be addressed