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The continued devaluation of the U.S. dollar and the industrial supply-demand balance between silver has increased the price of silver used in solder alloys. MacDermid Alpha Electronics Solutions has developed a number of low- and no-silver solder alloys to offset this continued trend in the increase in global silver cost. These alloys are appropriate for most applications, but not all. This article will describe the reliability, soldering performance potential of low- and no-solder alloys on different assemblies, and quantify the cost savings associated with using lower silver-bearing alloys.
As Figure 1 shows, the price of silver has doubled over the past year. MacDermid Alpha Electronics Solutions has a strict policy to never speculate on the future prices of tin, silver, or copper used to make lead-free alloys, but the current trend of the U.S. government to stimulate the economy by using deficit spending has caused economists to predict increased inflation and a reduction in the value of the U.S. dollar.
Silver traded on the London Metals Exchange (LME) and the New York Commodities Exchange (COMEX) is denominated in U.S. dollars. Any reduction in the value of the U.S. dollar generally increases the cost of metals trading on these exchanges.
However, using lower silver-bearing lead-free alloys should continue to be a lower cost alternative for circuit board assemblers who require a lead-free process. Silver constitutes 44% of the cost of metals used to create the most common lead-free alloy, SAC 305, as of June. That cost can be eliminated by using a silver-free SnCX Plus alloy (an advanced SnCu0.7 alloy) or reduced by 26% using a SACX Plus 0807 alloy.
Silver in lead-free solder has proven to enhance thermal cycling performance in demanding applications such as under-the-hood automotive assemblies (-40°C to 140°C THC), but typical consumer assemblies used in white goods, hand-held, remote control, and in-home audio-visual devices do not require the same thermal cycling resistance (0°C to 100°C). Low/no-silver soldering alloys are perfectly acceptable in these applications. In fact, data shows that reduced silver content increases the drop shock resistance of these devices.
Additional value from the low/no-silver alloys includes lower dross generation, particularly in wave soldering processing (scrap required to be recycled), and longer process life through reduced copper dissolution from OSP-finished substrates.
To read this entire article, which appeared in the September 2021 issue of SMT007 Magazine, click here.