The end is nigh for lead in solder, as our columnist Tim O’Neill wrote in July in CIRCUITS ASSEMBLY.
Rules governing use of the materials – Directive 2015/863, aka RoHS 3 – are coming online and will be in full force by 2019.
Suppliers have until July 22, 2019, to meet the stricter provisions, which include no more than 0.1% lead in medical devices, which are joining consumer, industrial and other electronics products on the effectively banned list.
In “Life After SAC 305,” Tim poses the question, What comes next? Already, the future of commonplace unleaded alloys such as SAC is being questioned. As Tim writes, “It is even feasible SAC 305 will be dislodged by a new de facto alloy that better serves the needs of the market.”
Poor SAC. It entered this world under duress – a much-debated compromise that standards bodies and major OEMs agreed on only after reviewing nearly 80 other alloys.
Indeed, iNEMI, the consortium driving the key industry research in the mid 1990s, had settled on SAC 396. Users blanched at the prospect of paying for all that silver, however. Then Iver Anderson at Ames Labs revealed melting temperature results of a lower-silver alloy, and industry made the jump to SAC 305. The grumbling has never really stopped.
A Norwegian scientist believes he may have a solution. As noted in Phys.org in July, Dr. Henrik Soensteby of the University of Oslo is working on an alternative alloy for optoelectronic devices that contains nothing but common – and essentially benign – elements. In conjuring up his alloy, Soensteby is mixing sodium, potassium and oxygen with niobium, a very strong metal typically used in steel. While niobium dust is reported to cause eye and skin irritation, it reportedly is nontoxic, at least in the volumes used.
It’s not so clear yet how much niobium would be needed. Brazil is the biggest supplier of niobium, producing more than 85% of it each year. Other sources include Zaire, Russia, Nigeria and Canada. World production is relatively light: around 25,000 tonnes per year. Some scientists believe ample supplies are still in the ground. There’d better be. Some 5 million tonnes a year of lead ores are mined each year, although obviously not all that goes into electronics.
Insofar as application goes, Soensteby is optimistic he can use atomic layer deposition (ALD), a vapor-phase method that uses gas at controlled temperatures to stimulate a reaction with the substrate; the output is thin films. It is an emerging technology in semiconductor manufacturing. There are many, many questions, of course. First and foremost, does the alloy actually, you know, work? Also, ALD typically involves higher temperatures than are used in electronics assembly. Is it compatible with today’s packaging, especially given the trend toward lower-temperature processing?
On that point, metallurgists I contacted aren’t so sure. As one 40-year veteran of soldering materials noted, “The fundamental challenge is that it not only requires a change to the materials but also one to the process.” An applications engineer at a solder supplier added that while silver’s toxicity profile leaves it open to elimination, the periodic table doesn’t offer many superior alternatives that haven’t already been tested and discarded.
Another industry metallurgist commented, “Good academic/material research, but years away from prime-time use. And note that the use of lead in electronics as cited in the article was very one-sided, with omission of the full story on the use of lead in electronics in the industry. More lead is used in automotive batteries than in electronics.”
It won’t stop the blue sky work, nor should it. Meanwhile, other potential game-changing technologies, such as 3D printing (see Simon Fried’s article on pg. 36) or Joe Fjelstad’s solderless Occam process, remain in the periphery, waiting for their moment.
Materials science is the most exciting area of electronics today. We may make fun of folks who walk around with smartphones seemingly permanently tethered to their ears, but we also have them to thank for demanding the technology advancements that make it so.
P.S. I hope to see you this month at PCB West in Santa Clara, the largest trade show for electronics design, fabrication and assembly in the Silicon Valley. There are more than 75 presentations, including three full days' worth of free talks, plus more than 100 exhibitors.