An obvious disadvantage of lead-free assembly is that the oven must be hotter and therefore will use more electricity. But is the extra amount of electricity significant? Bill O’’Leary claims that a typical SMT oven uses $7K of electricity a year at $0.072/Kilowatt hour (Kwh) or about 100,000 Kwh for a typical SMT line per year. That number strikes me as about right, as a household uses about 5-20,000 Kwh per year.
In the late 1990s there were 35,000 SMT lines in the world, at a 3% growth rate that would be about 50,000 lines now. So worldwide SMT reflow oven electricity use would be about 5E9 KWhr (50,000 ovens x 100,000 Kwh/per year) world wide. World Electrical use is about 150,000E9 Kwhr
With most heat loss be due to convection the increase in energy use will be approximately proportional to the difference between the oven temperature and the room temperature (25C). An oven processing tin-lead solder would run at about 210C versus lead-free’s 250C. So the added energy for a lead-free oven would be about (250-25)/(210-25) or about 22% more. So if all assembly lines in the world are SMT the added energy use would be about 0.22x 5E9 Kwh = 1E9 Kwh. The cost of this extra electricity would be about $100 million (US) at $0.10/ Kwh. The electronics industry generates about $1.5 trillion in sales. So this added cost would be about 0.0067% of sales. Since world electrical use is about 150,000 E9 Kwhr per year, this increase is about 1/150,000 of all of the electrical use or 0.00067%.
So although more electricity is used, the increase is not significant to the value of the electronics sold or the total world use of electricity.
Thinking about higher temperatures reminds me that my Indium Corporation colleague Dr. Ning-Cheng Lee has authored a paper on a high melting temperature lead-free solder based on a BiAgX® alloy system. Higher melting temperature solders are often needed in what is referred to as a solder hierarchy. Solder hierarchies have solders that melt at decreasing temperatures in multiple soldering steps, starting with the highest melting solder.