Lead has, for years, been a key ingredient in solder used in commercial applications. Despite the risk it poses to the environment, and to the health of the people doing the soldering, lead makes it relatively easy to lower the melting point of the solder, and thus the material has remained a common one, found widely in traditional soldering equipment. It is most often paired with tin in proportions ranging from around 50:50 to 60:40 in favour of tin.
Alternatives come in the form of solders which incorporate things like bismuth, silver, copper and zinc.
Why is Lead Used?
Given the environmental cost of lead, you may be forgiven for wondering why it’s still in the supply chain at all. The fact is that, as well as altering the melting point, lead is cheaper than the available alternatives. Given the quantity of solder needed for the manufacture of even small electronics, the use of leaded solder allows for significant savings for manufacturers. Until the alternatives can be made more affordable, it is likely that lead will persist.
German manufacturer Opes are among a string of German businesses looking to reverse this trend, with their development of an off-grid photovoltaic solar module which uses lead-free solder. The company which commissioned the project, Biolite, are heavily involved in home-solar solutions in African countries, where the electrical infrastructure is unreliable, and the need for energy independence greater. In this part of the world, lead pollution has not been properly managed, and the lead contained in fly-tipped car batteries is often the cause of groundwater pollution and widespread lead-pollution.
Among the challenges for the company was the tolerance of the photovoltaic cells to higher temperatures. This is a problem that is to be found on many sensitive components, and a major reason that lead is still used in commercial manufacture at all. The higher the melting point, the more extremes of temperature the more sensitive components are forced to endure, and the greater the rate of failure.
When temperatures are lower than they might otherwise be, the connection between the solder, board and component can be less than optimal. This, over time, can lead to more frequent and premature failures, especially in outdoor equipment like photovoltaic solar panels.
What does the law say?
The European Union’s Waste Electrical and Electronic Equipment (WEEE) Directive came into force in early 2003, and the Restriction of Hazardous Substances (RoHS) Directive followed a few years later. These limit the viability of lead-based solder in cheaper products.
With that said, the long-term viability of the alternatives is not fully understood, and so it remains likely that lead will remain a key ingredient in certain safety-critical applications, like in aerospace and medicine.