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Lead Free Series: Changing the Factory to Lead-free
December 31, 1969 |Estimated reading time: 3 minutes
With all preparation work accomplished, it becomes time to implement lead-free in the factory. This article is intended to point out the most important practices and issues critical to the success of lead-free implementation.
By Jennie S. Hwang
Changing the factory to lead-free may be taken as an extraordinarily complex endeavor. In addition to usual logistics, there are three main steps to accomplish the task: understanding some basics of lead-free technology, making the "right" selection of process and materials while recognizing respective merits and constraints, and then installing these selections into the existing infrastructure systematically. Many production lines around the world have demonstrated a smooth transition in changing the factory over to lead-free.
Two parallel approaches (drop-in and modification), and thus two methodologies can be taken to pursue the implementation. Simply put, the key distinction between them is process temperature. At the board assembly level, the process temperature refers to reflow and wave soldering temperature; that is, whether the commitment of a production operation is to an elevated process temperature or to the same process temperature as the existing setup.
Regardless of the approach, a critical point is that the process committed to must be "synchronized" with the materials and components selected. Materials include printed circuit board (PCB) and component ones, as well as solder alloys. The properties and behavior of lead-free solder materials have been thoroughly researched and tested for more than 15 years.1 The performance coincides with the teachings of materials science and engineering, and test results were verified on the production floor as well.2
Overall, in implementation of lead-free, the industry will continue to work within the existing SMT manufacturing infrastructure. Today's SMT manufacturing evolved over more than two decades. During this period, many production-level defects, problems and issues have surfaced, and thus far, all have been alleviated and resolved. As new designs and products continuously are introduced, new and different issues surface. It is crucial to identify clearly and separate SMT production issues per se from lead-free-related ones.
Another important point is that established and proven SMT manufacturing practices should be diligently observed for lead-free production. What has been learned is immensely valuable, resulting in today's best practices. These best practices determine production yield and the long-term reliability of the assemblies produced.
What constitutes best practices in SMT assembly to crank out high-throughput production? The materials used in the production system must be capable of delivering performance latitude, and the process established is able to provide an operating window. With the material performance latitude and process operating window in place, demands from diverse and versatile circuit boards then can be accommodated, and variations inherent in an SMT production operation can be absorbed without impairing production yield and product quality.
Conclusion
In real-world performance, material properties and behavior (such as in solder joint formation) cannot be forced by a process, nor unduly embellished from its true performance by any means. In the long run, only the true performer prevails. With the right choices and clarity about the reasons behind these choices, you are in control in converting your factory to lead-free.
References
- Jennie S. Hwang, "Environment Friendly Electronics: Lead-free Technology," Electrochemical Publications, Great Britain, 900 pages (ISBN: 0 901 150 401)
- Jennie S. Hwang, "Lead-free Implementation and Production," McGraw-Hill, to be released winter 2004.
Dr. Jennie Hwang, an SMT Advisory Board member, has been elected to the National Academy of Engineering, inducted into the WIT International Hall of Fame and named an R&D-Stars-to-Watch. During 23 years of SMT manufacturing, she has helped improve SMT production yield and solved various field failure and reliability issues. She has also shared her experiences and knowledge in authoring more than 200 publications, including the sole authorship of several textbooks and in lecturing to more than 10,000 professionals worldwide. She holds two M.S. degrees in organic and physical chemistry and a Ph.D. in materials science and engineering. Contact her at (216) 839-1000; E-mail: JSLHWANG@aol.com