Component termination finishes containing lead have virtually been discontinued. Well over 90% are now Pb-free, and many suppliers consider SnPb terminations to be special orders. Pure Sn is the usual choice for component termination finishes today. Nickel/Palladium/Gold is a common Pb-free alternative to Sn, but at an additional cost.
So why all the fuss? Solderability for starters, as Pb-free solders have decreased wetting ability. Pb-free component finishes and solders typically require higher soldering temperatures which will affect cost, reliability, and rework. Then there’s Pb-free solder durability, as Pb-free interconnects are less reliable at higher temperatures, vibration, and shock. This is not a big issue for consumer products because of low stress levels, but not so for aerospace applications. For low stress, Pb-free is better, and for high stress, SnPb is better.
That’s not so bad you say? Well, the biggest bug-a-boo of all is Pb-free Tin reliability–a.k.a. Tin Whiskers! That single issue which has plagued the Aerospace and Military community for decades is now compounded by the RoHS directive.
The prevention of Tin Whiskers continues to challenge Aerospace engineers today. In-depth studies continue to show that this phenomenon can be a deal killer, particularly for space-bound electronic products. How are engineers working with component suppliers to combat this menace? Check back for an upcoming Part 2 of this blog series about Tin Whiskers as we discuss some avenues to attack this issue, and the levels of success for each.