Lead-free Solder
December 31, 1969 |Estimated reading time: 2 minutes
This column is the first of a three-part series on lead-free solder.
Ray P. Prasad
Tin/lead solder is the most commonly used solder for electronics assembly. How-ever, in the last year, there has been an industry-wide push to convert to lead-free solders. The reason behind the push is the increased awareness concerning lead use and its adverse effects on human health.
Lead is linked to health hazards such as disorders of the nervous and reproductive systems, and delayed neurological and phys-ical development. Lead poisoning is particularly damaging to the neurological development of young children.
There are laws that control lead use. For example, lead usage in plumbing, gasoline and paint is heavily regulated. Lead use in consumer paint has been banned since 1978 in the United States, and additional regulations are under consideration in the United States, Europe and Japan.
Table 1 shows the amount of lead used in various products.1 Storage batteries account for 80 percent of the lead in use. Electronic solder accounts for approximately 0.5 percent of all lead usage. Even if lead use in electronic solder were to be banned, it would not solve the overall lead poisoning problem. However, the 0.5 percent lead used in electronics soldering still amounts to significant lead use.
Lead Replacement Elements
The electronics industry is looking into lead-free solders that can replace the universally accepted, and widely used, tin/lead solder. Research and development efforts are focused on the study of potential alloys that provide physical, mechanical, thermal and electri-cal properties similar to those of tin/lead eutectic solder. The metals that can replace lead and their relative costs are shown in Table 2.
In addition to cost, it is also important to understand the supply and demand of the elements that are being considered as lead replacements. For example, as shown in Table 3, an alloy containing bismuth (Bi) may not be desirable from an availability standpoint: The current available supply of Bi could be used up completely if this alloy were to be used extensively by the expanding electronics industry.
As is obvious from the relative costs of potential replacement metals for lead shown in Table 2, many lead-free solders will be much more expensive than the tin/lead solders they are replacing. For example, In is one of the leading elements used to replace lead. But it is a semiprecious metal and is almost as expensive as silver. It should be noted, however, that the high cost of a proposed solder alloy is not as significant in determining the final product cost as it may first appear. Because of the small quantity needed, solder cost in an assembly is almost insignificant in comparison to other cost factors such as components, bare board and assembly. The properties of the selected alloys are very important - I will discuss them in my next column.
REFERENCES
1 Lead and the Electronics Industry: A Proactive Approach, May 1995 report available from National Center for Manufacturing Sciences, 3025 Boardwalk, Ann Arbor, MI 48108; (313) 995-0300.
2 Duane Napp, "NCMS Lead-free Electronic Interconnect Program," Proceedings of Surface Mount International, 1994, p. 425-31.
3 Jennie S. Hwang, "Overview of Lead-free Solders for Electronics and Microelectronics," Proceedings of Surface Mount International, 1994, p. 403-21.
RAY P. PRASAD is an SMT Editorial Advisory Board member and author of the text book Surface Mount Technology: Principles and Practice. He is also founder of the Ray Prasad Consultancy Group which specializes in helping companies establish strong internal SMT infrastructure. Contact him at P.O. Box 219179, Portland, OR 97225; (503) 297-5898; Fax: (503) 297-0330; Web site: www.rayprasad.com.