When the electronics industry shifted to lead-free solder in the wake of the European Union passing the Restriction on Hazardous Substances (RoHS) directive, naysayers predicted a wave of product failures. Well, where are the failures?
Dr. Ronald Lasky, Dartmouth professor of engineering and a frequent blogger on solder, claims the transition to lead-free was a grand success. “A lot of people claim that lead-free solder is not as reliable as lead-based solder,” Lasky told me. “We’re now five years into the implementation of RoHS, and we’ve made $3 trillion work of electronic. We haven’t really noticed any big change in reliability.”
He says long-term reliability is still a mystery, since most of the products with lead-free solder have not been deployed that long. Yet he points to benefits of today’s solders, noting they are easier to mass-produce when pitches are tight. When high-density semiconductors are packaged in small form factors, using lead-free solder can result in boards with fewer problems. “Lead-free solder doesn’t wet well, so you can get better lead spacing,” Lasky says.
He notes a study by Motorola where design engineers built identical boards with lead-based and lead-free solder. The results showed that leads printed close together shorted out when lead solder flowed during melting.
Lasky concedes that high temperatures needed to melt lead-free solder have created some problems. “Moisture sensitivity is a big issue that’s often overlooked,” he says. “Much of the moisture research was done for lead-based temperatures, not the higher temperatures of lead-free processes.”
He explains that if you have a moisture rating of four for lead, it might be five or six at lead-free temperatures. “This new situation can cause problems such as popcorning, as well as board warpage.”
Lasky will discuss many of the facets of designing and processing boards using lead-free technologies during the IPC Midwest conference on September 21 and 22 in Shaumburg, Ill.