Getting the Lead Out

Most people have heard the expression “Get the Lead Out” to refer to someone who is moving too slowly; implying that they can move faster if they get rid of weight that is slowing them down. A different and fascinating way to hear this expression is to take it literally, to see what it means, why this is important, and how long it has taken.

The ancient Romans not only used lead pipes for water, they preferred it for vessels to hold wine, saying it made for a sweeter taste than copper vessels. There has been a lot of speculation, with scientific basis, to show that lead poisoning, especially of the elite, may have been a major contributor to the fall of the Roman Empire. Lead was causing us problems over two thousand years ago!

Lead has been shown to be such a major contributor to health problems that lead is banned from paints currently used in most countries. The problem of young children getting lead poisoning from eating old paint chips in dilapidated inner city homes is still a problem today. Retardation in toddlers has been traced to the acid in orange juice leaching lead from the glaze on drinking cups.

Why are we using lead in the first place? Simply said, it has very desirable features, if one can ignore the fact that it is killing us. The Romans found the lead to be easy to work with for pipes and containers. Lead can help make paint more elastic so that it does not crack as easily with some expansion and contraction with temperature. It also can contribute to a nice glaze on ceramic cookware, if you do not mind poisoning your family or blowing out your microwave due to its conductive properties.

The EU directive, Restriction on Hazardous Substances, RoHS, came into effect on July 1, 2006, prohibiting the inclusion of significant quantities of lead in most consumer electronics produced in the EU. This has become the de facto standard that we follow. While the elimination of lead affects many industries, the effect on the electronics industry is especially large. The major questions are: what do we use in place of lead and what new problems will be introduced?

In electronics, lead, especially when combined with tin, makes a great “glue” to hold wires together and components onto printed circuit boards. In combination with tin, the melting point of the compound can be lower than for either lead or tin separately (the eutectic point). Not only is it a good conductive glue, its melting point is nearly ideal. At about 185C (355F), it does not melt until well above commercial, industrial and military operating temperatures. And it melts at a temperature much below the point where plastic packaging melts or other damage is done to sensitive components.

Tin, combined with other metals such as silver and copper, show much promise for lead free solder, but there are many metallurgical issues such as tin whiskers and joints becoming brittle. Each combination has a higher melting point than the lead-tin alloy. With the same maximum processing temperatures for the components, this is a significant narrowing of the window of acceptable processing temperatures. These, and many related problems are being solved, but there is much more work to be done.

The next time you hear “Get the Lead Out” remember this has been a problem for humanity for over two thousand years and we are still working on the problem.

Date

2014-08-09