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94 DESIGN007 MAGAZINE I JUNE 2020 Reason 4 Most lead-free solders contain substantial percentages of silver (~3–4%), and silver is toxic to microbial life and fish larva. This has often been ignored perhaps because it was felt that it would be recaptured and recycled. Reason 5 The global conversion cost to lead-free ran to perhaps $100 billion or more with no real benefit [2] . The conversion cost continues to this day. Reason 6 Lead-free solders typically require signifi- cantly higher temperatures to solder, meaning that more energy is required and will be re- quired on an ongoing basis. The higher tem- peratures required also negatively impact and influence the PCB material choice, as well as PCB and semiconductor devices and other component reliability. Reason 7 The definitive reliability of lead-free sol- ders remains elusive to this day. Alloy after alloy is trotted out to run the assembly gaunt- let with varying degrees of success and it re- mains an uncertainty how well they will per- form over time, as there are numerous effects (cracking, voiding, tin whiskers [3] , etc.)—all of which have causes that remain, in many cases, and are neither well understood nor predictable. Reason 8 Several early studies from both universities [4] and the U.S. EPA [5] (and which were large- ly ignored) indicated at the time that, on-the- whole, lead-free electronics appeared to be much less environmentally friendly than those using tin-lead solder. Again, the primary case against lead was its toxicity, which for lead— as metal or in an alloy—was and remains un- likely to cause harm unless directly ingested. (Most common lead salts, hydroxides, chlo- rides, and sulfates are insoluble in water and many acids.) Reason 9 Traditional tin-lead solders continue to be used by military and aerospace manufactur- ers that are exempt because they must have the highest levels of reliability, resulting in a dual path that has created an ongoing logisti- cal headache; this is becoming ever more chal- lenging as sources of tin-lead finished compo- nents continue to dry up. Reason 10 Interconnection innovation remains hob- bled as engineers are diverted from solving real technological problems to solving a "lead problem" that never existed in the opinion of most scientists. Reason 11 Tin resources have always been significantly lower than those of lead; as a result, new tin mines were opened often in areas where rival factions fight to the death for control of the mines. It is also highly unfortunate that some of the richest tin mines are found in rain for- ests, which must be clear-cut to get to the tin deposits, contributing to global warming [6] . Reason 12 The provisions of the Waste Electrical and Electronic Equipment (WEEE) regulations mandate the recycling of electronic products, making all the concerns of lead in electronics completely moot. Conclusion As the timeless adage goes, "The road to hell is paved with good intentions." If you can feel the heat as you are trying to make your prod- ucts better and more reliable, you may well get the impression you have already arrived there. Then again, as Winston Churchill sage- ly said, "When you are going through hell, keep going." Keep up your spirits, and stay well. FLEX007 Editor's Note: Read the Solderless Assembly for Electronics: The SAFE Approach e-book writ- ten by Joe Fjelstad to consider an alternative

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