Will lead-free mean unreliable?

 - September 12, 2006, 12:59 PM

New environmental laws enacted by the European Union over the summer could mean that the avionics of tomorrow will be less reliable than radios built before Charles Lindbergh’s solo Atlantic crossing. But before anybody vows never to buy another new piece of aircraft electronics, here’s the full story.

Chip makers began transitioning to lead-free components several years ago after the EU announced a clamp-down on a number of environmentally harmful substances–including lead–in electronics. The ban and an ensuing global switch to lead-free devices have resulted in the use of mainly tin for electronic solders in everything from PCs to cellphones. So far these solders have demonstrated some serious reliability shortcomings.

For this reason, aerospace and defense industries are exempt from the EU rules. But avionics manufacturers eventually will be swept along in the shift to lead-free electronics because the global electronics industry serves as aerospace’s basic supply source.

“Whether the avionics industry makes a conscious decision to change or not, our suppliers are switching to lead-free electronics, and that means to a degree we will have to switch as well,” said David Hillman, a material and process engineer at Rockwell Collins. “We as an industry need to pay a lot of attention to this issue and act accordingly.”

‘Tin Whiskers’ a Concern

The environmental restrictions necessitating the transition to lead-free electronics became law in Europe on July 6. Avionics manufacturers by and large have not incorporated the lead-free tin solders into their products and are unlikely to do so until the reliability of these alloys improves. A key issue with the new finishes is the formation of so-called “tin whiskers” on the solders themselves. If these whiskers (a metallurgical phenomenon whereby the metal grows tiny crystalline hairs) touch whiskers from another solder, or grow long enough to reach a nearby solder, they can cause shorts, leading to component failure.

The tin-whisker phenomenon is not well understood by scientists, but what is recognized is that rugged, high-performance operating environments (such as exist in the avionics bays of airplanes) only amplify the negative effects of whiskering. In response to the problem, Boeing, Airbus, the Aerospace Industries Association (AIA) and others have formed a working group to study the impact of the lead-free transition in aviation and develop uniform manufacturing processes. The group, led by Boeing Phantom Works technical fellow Lloyd Condra, recently published a number of documents to help the aerospace and defense industries deal with the transition.

Before anybody gets the idea that the avionics of tomorrow will be no more reliable than, say, the infamous Lucas electrics in British cars of the 1960s, it’s only fair to share an important, if little-known, fact about electronic component reliability: many of the radios that were manufactured before Lindbergh’s heyday still work today.

In fact, solders made from alloys of lead and tin have been used for more than 100 years with excellent reliability, far beyond the typical lifecycle of modern avionics. While tin whiskering and other technical concerns about lead-free avionics certainly need to be studied and addressed, engineers say there is no reason to think that the avionics built four or five years from now won’t easily meet accepted reliability standards.

“The processes in the aerospace industry that were developed by the AIA are designed to ensure that none of the products we design and field have any of those kinds of reliability problems,” said David Humphrey, a principal engineer at Honeywell. “It’s not allowable, it’s not good business and we would not do it.”

Industry-wide Collaboration

Engineers from around the world have been involved for the last five years in research projects aimed at studying new materials to replace lead in electronics. Combining tin with small amounts of silver and copper has shown promise for improving reliability to levels equal to the old tin-lead solders, researchers say. Zinc-nickel, aluminum-manganese and a number of other alloys are also being studied with the goal of finding a better blend before the wide-scale transition to lead-free avionics.

“There is a significant effort out there to determine all of the characteristics of those solders as they would behave in our environment,” Humphrey said. “In addition, on the AIA working group there are 50 to maybe 100 people, all experts in their fields, who are collaboratively working on the process documents,” which are intended to serve as a uniform approach to avionics production for the entire industry. A key element of that approach, he said, will be to closely monitor component reliability, ensuring that future avionics will be every bit as dependable as current-day equipment.