Dr. Matt O’Keefe, associate professor of materials science and engineering at UMR, is testing solder joints to find out how lead (tin-lead) and lead-free (tin-silver-copper) solders compare. His work is in collaboration with Boeing-Phantom Works, Northrop Grumman, Air Force Research Laboratory and the Center for Aerospace Manufacturing Technologies (CAMT), which is housed at UMR.
Consumer electronic equipment, like cell phones and toys, often use lead solder. Because they have a short life span, within a few months or years the products end up in landfills, where the disposed lead can leach into the water supply, risking human health and the environment.
Starting July 1, 2006, the EU’s Restriction on Hazardous Substances Directive will make “lead free” a requirement for EU member countries and for those wanting to sell electrical and electronic equipment in the EU. Although the aerospace industry is specifically excluded from the new requirements, the industry “will feel deleterious effects,” O’Keefe says.
“Many aerospace products are designed and produced by suppliers who supply to commercial customers worldwide,” O’Keefe writes in this month’s issue of Assembly magazine. “For economic reasons, these suppliers may deliver lead-free products to all of their customers.”
Unlike consumer electronics, military electronics are often repaired in the field, sometimes aboard a ship or at a distant base where space, materials and repair equipment are limited.
“If a solder joint breaks in your cell phone, it’s not as big of a concern because people buy a new one each year,” O’Keefe explains. “It’s a little different if the joint cracks in an F-15’s radar. These components need to have higher reliability.”
As the lead free requirement becomes increasingly widespread, aerospace contractors will have to repair conventional tin-lead solder assemblies using lead-free solder or replace them with lead-free components.
Solder joint performance following field repairs is especially critical, because the operating conditions are “harsher from an environmental and mechanical standpoint” than in most commercial or consumer sectors, O’Keefe adds.
In O’Keefe’s initial tests, shear strength was generally higher for lead-tin solders and lower for lead-free solders. Mixing the two alloys demonstrated shear strengths in between the two individual alloys.
“The preliminary data indicates that incomplete removal of the lead solder during repair with a lead-free solder may actually be beneficial to the reliability of the joint,” O’Keefe says.
More study is needed to understand how lead-free solder behaves, but time isn’t on the aerospace industry’s side. Suppliers have already started sending companies like Boeing some components that are lead-free.
“We have roughly 50 years of knowledge about lead-tin solder so we know how it behaves,” O’Keefe says. “How will lead-free components hold up? That’s the question everyone wants to answer.”