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New Materials and Processes Enable Lead-free Solder
December 31, 1969 |Estimated reading time: 2 minutes
Joining components to circuit boards or microelectronic packages using lead-based solders is common practice in today's industry, but lead has obvious health and environmental drawbacks.
By Tim Weihs
With these realities becoming issues that no longer can be ignored, the microelectronics industry, as well as governmental bodies have developed a keen interest in lead-free solders and joining processes. Such interest is shown through the current well-known legislation requiring any electronic product sold in the European market to use lead-free solder beginning in 2006. Other regions are expected to follow suit. Realizing the changing tides, many electronics companies have already begun to promote lead-free-produced goods to their competitive advantage.
One of the main reasons for using lead-based solders is their relatively low melting temperature compared to other solder materials, which reduce thermal exposure during a reflow furnace cycle. If an assembly needs to reflow four times, for instance, four different solders are required to ensure bonds made in the first reflow cycle are not damaged in subsequent cycles. The first reflow cycle uses a solder with the highest melting temperature, the second reflow uses the next highest melting temperature, and so on. As a result, lead-based solders are extremely useful in limiting device exposure to high temperatures.
Manufacturers are exploring new materials and processes to bond components to circuit boards using lead-free solders.
Efforts within the industry currently focus on removing lead from electronic assembly processes without sacrificing capabilities enabled by lead-based solders. Primary areas of innovation include:
- New Joining Materials. Materials manufacturers are developing and testing alternate lead-free solders with both low melting temperatures and high reliability. These manufacturers also are developing electrically conductive adhesives with low curing temperatures and moderate conductivities.
- New Joining Processes. New joining processes eliminating the need for lead-based solders also are under development. Mounting more components in each reflow cycle promises to reduce the number of reflow cycles. This would help minimize dependence on solders with low melting temperatures. One company* has a rapid, localized heat source, reportedly eliminating the need for a furnace. The heat source product** is placed at the interface to be bonded. Through a chemical reaction, it provides heat to melt the surrounding solder. Localizing heat to the bonded interface melts any solder while the components themselves remain at or near room temperature. This process not only eliminates the need for lead-based solders with low melting temperatures, but also reduces thermal damage to heat-sensitive components and creates electrically conductive interfaces.
Conclusion
Technologies that help to overcome dependence on lead-based solders continue to generate interest. Lead-free materials are being researched while new processes are being developed to eliminate the need for low melting temperature, lead-based solders. Researchers are discovering that changes in the current joining processes not only support this progression away from lead, but also reduce thermal damage in resulting microelectronic products.
*Reactive NanoTechnologies Inc. (RNT)** Nano-structured NanoFoil.
Tim Weihs, Ph.D., co-founder, president and CEO, may be contacted at Reactive NanoTechnologies Inc. (RNT), 111 Lake Front Drive, Hunt Valley, MD 21030; (410) 771-9801; Web site: http://www.rntfoil.com