A Leaded Engineer in a Lead-Free World

By Terry Costlow, IPC online editor
Re-posted with kind permission of IPC - www.ipc.org

Leaded, unleaded technologies continue to challenge high reliability fields.
Many engineers have already converted to lead-free solder, but the transition is still a relatively new trend for engineers in high reliability fields.

Though migrating from decades-old manufacturing processes is not simple, specialists say that it's yet another step in the ongoing evolution of electronics. Though the military, aerospace and other industries can still use lead solder, it's disappearing. That's forcing them to learn how to intermix the remaining lead solder parts and processes with lead-free technologies and techniques. That is a major change.

"We're moving from a system that was simple to one that's more complex," said Dave Hillman, principal materials and process engineer at Rockwell Collins. "We're dealing with new failure modes, things like tin whiskers that cause failure types we haven't seen before."

To Hillman, this is simply another in a series of changes. The electronics field is continuously undergoing an evolution, and the shift from leaded to unleaded solders is yet another step. However, the timeframe makes it an especially challenging transition.

"Tin-lead solder has been the basis of all electronics for 60 years. Changing all that in three or four years is not optimal," Hillman said. "Lead free is doable, but we need more understanding." He's far from the only one who feels that the transition is a challenge like many others that can be met by paying close attention to detail. Many people are placing too much blame on solder. When problems with solder joints arise, there are often many other factors that come into play. "You can't blame everything on solder," said Carol Handwerker, professor of Materials Engineering at Purdue University. "That's just a band aid for covering up other errors in the overall process. Things like design layout and tests that weren't done correctly are also major factors."

They'll be discussing this change during the opening session at IPC Midwest in Schaumburg, Ill., on Sept. 23. The Wednesday morning session, "A Leaded Engineer in a Lead-Free World," will explore the challenges facing engineers who work in fields that are exempt from lead-elimination regulations.

Hillman hopes to convince attendees that the processes don't require design and manufacturing engineers to do things they've never touched on. Aspects like the high melting temperature of some alloys are similar to challenges posed by some longstanding high reliability materials and processes.

"We've used gold, which melts at 2,000 degrees F. It doesn't melt at normal soldering temperatures, but it diffuses into the surrounding metals," he said.

Similarly, lead-free materials that melt at higher temperatures can be meshed with lower-temperature lead processes, he explained. Perhaps one of the biggest challenges is to understand what went wrong after boards with lead-free solder fail.

Several working groups have spent thousands of man hours of research trying to build this knowledge base. The Aerospace Industries Association has shepherded efforts that include its Lead-free Electronics in Aerospace Project Working Group, augmenting tons of ongoing projects by iNEMI and IPC.

"A lot of people in industry, academia and research are working to make sure we have the most reliable assembly processes for the military and other high-reliability fields," Handwerker said. "We need to understand how to track everything as we go from design through to rework."

That level of understanding is growing as more commercial products provide long-term reliability information in real world conditions. The European regulations began in 2006, and many products made the transition to lead-free technologies before that change. That means many products have been in the field for five or six years.

Though that's a fair amount of time, it's still short compared to the lifetimes of airplanes and most ground vehicles. Ten years is a disappointing lifetime for trucks and off-highway equipment, for example, while five years is probably beyond most cell phone lifetimes.

Attendees at the IPC Midwest session will get knowledge from a number of engineers who have worked in the high reliability field for years. Hillman and Handwerker will be joined by three more representatives from the aerospace and automotive fields.

Linda Woody of Lockheed Martin Missile & Fire Control, Stephan Meschter of BAE Systems Platform Solutions and Mark Fulcher of Continental AG will also present views and data that will help those who attend understand the many nuances of combining leaded and unleaded solder in high reliability applications.

With kind permission of IPC - www.ipc.org