A reader writes:
I attended your seminars last year at the SMTAI Technical Conference in Chicago and Boston and discussed with you LF implementation and manufacturing. I must say that both of your presentations were very beneficial to me.
Recently, we received a BOM from our CM which has attached all the materials that they use to manufacture our boards. Certificates/test results of alloys were also attached. The SAC Alloy analysis showed that Lead (Pb) in all three types of SAC alloys found to be 467, 527, 254 ppm respectively. We were under the impression that any SAC alloy would not contain any lead even though up to 1000ppm is acceptable by the EU directive.
Could you please comment on this, should SAC alloy have any lead in it?
Thank you for your kind comments about my workshops. I'm glad they were helpful.
As I write a response, I am looking at my left thumb nail. It is composed mostly of thumb nail material (H, C, Ca, O, etc), however about 0.1% or so will be a wide variety of trace elements, almost certainly among them will be Pb. The quantity of Pb is likely very small, maybe in the ppB range but it is not 0. (As far as I know I am healthy, trace elements are ubiquitous even in the healthiest of people.)
The same is true of metals, there will always be traces of other elements even in very pure metals. Canadian Gold Maple Leafs boast that they are 99.99% pure gold (i.e 100ppm impurities). These types of purity come with a cost.
Hence, it would be expensive to get SAC with Pb < 100ppm. Since the limit in the EU is 1000ppm, most companies supply at < 500 ppm Pb or so. It is my understanding that even the 1000ppm limit on Pb is a disappointment to solder recyclers. It appears that it is hard (read: expensive) to take scrap tin-lead solder and reclaim the tin at <1000 ppm Pb levels.
Bottom line: Expect Pb at < 1000ppm in SAC so that the price is affordable.