A structured approach to lead-free IC assembly transitioning

Market forces, trade restrictions, and customer perceptions rather than environmental realities have driven the lead-free movement. However, it cannot be turned around. Consequently, manufacturers, suppliers, and industry consortia have all been working towards a common acceptable drop-in replacement for the standard eutectic SnPb. Most U.S. and European groups support the use of SnAgCu alloys for surface mount applications. For instance, NEMI has recommended Sn3.9Ag0.6Cu as an industry standard for lead-free solder paste (with Sn0.7Cu for wave soldering), and is currently assessing its manufacturability and reliability. Similarly, SnAgCu alloys have been recommended for solder balls to be used in array packages. Unfortunately, there has been no recommendation for a lead-free finish for leaded packages, which still constitute the largest portion of the worldwide semiconductor packaging production. IC suppliers had to struggle to evaluate the various lead-free finish options available, and assess the resulting impact of the transition on their manufacturing logistics. This paper will provide the highlights of a structured program, at National Semiconductor Corp. to transition from SnPb to lead-free IC manufacturing.