NEMI has selected what's called Sn3.9Ag0.6Cu, a tin-based alloy that replaces lead with 3.9 percent silver and 0.6 percent copper. That material is suggested for the solder reflow applications used in about 70 percent of the pc boards produced today.

For wave soldering, which uses more solder at higher temperatures, NEMI is suggesting two alloys: Sn0.7Cu, a tin-copper alloy with 0.7 percent copper, and Sn3.5Ag, which has 3.5 percent silver.

The alloys were chosen by a task force whose work began when it appeared that governments around the world had become intent on eliminating lead in the growing number of electronic products that made it to the global scrap heap. Among NEMI's goals is to avoid splintering the efforts to advance this movement.

"One of the things we're pushing for is a standard replacement," said Jim McElroy, executive director of NEMI. "Think of an electronic manufacturing services company. Imagine the havoc if each customer has a different solution, and they need to change lines for each solder. In reality, that would stop the implementation of lead-free solder. We want to get everyone on the same sheet of music. That will also mean the cost issues will be resolved."

Now that NEMI has made its recommendation, other organizations will go over it with a fine-tooth comb.

A spokesman said the Institute for Interconnecting and Packaging Electronic Circuits (IPC; Northbrook, Ill.), the trade association for the circuit board assembly and manufacturing industries, would be examining NEMI's findings and methodology before deciding whether IPC will also endorse the alloy. "We're in favor of a single global solution," the spokesman said.

Questions remain

By focusing future research on these alternatives, NEMI hopes to quickly answer the two main questions — cost and reliability — surrounding lead-free solders. Though several companies are already using lead-free solders in a variety of products, they represent only a tiny fraction of the circuit boards produced annually.

New solders will cost more than the ubiquitous eutectic tin-lead solder, but that may not be a big issue.

"The materials themselves, the solder pastes, represent a small amount of the total system cost, though we might see some added cost of the paste itself," McElroy said. "There may be other cost issues driven by the fact that these solders require higher temperatures. But I believe that at the end of the day we'll be talking about numbers smaller than 1 percent."

The changes in material will likely create questions about reliability. However, proponents of lead-free solder note that companies that have used lead-free materials for years report no major changes in reliability.

What remains to be seen is how quickly lead-free materials will be adopted. Interest has spiked in the past 18 months, driven in part by the belief that consumers will pick lead-free products if there is little or no cost premium over those with lead.

"I believe people will make the change for marketing reasons," McElroy said. "People have found that when they tout a product as lead-free, especially a consumer product, it can provide marketing clout. We've already seen companies starting to change for that reason."

McElroy noted that the early adopters could make the switch relatively fast.

"The actual conversion process could be done in a year or so," he said. "What will take longer is to alter everything in components. There are thousands and thousands of components used worldwide, and converting all of them may take time. Until that's done, companies could change their solder processes but still use components with tin-lead solder on their leads. There are some logistics issues for this type of intermixing, but things are fairly robust, so the processes will allow this hybrid phase."

For the designer, he said, "there may not be much difference other than the temperature the components have to survive. They may have to specify parts that meet new requirements."