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Musings on Electronics Assembly Metals: Gold Unified a Country


In Ken Burn’s  excellent miniseries The Civil War, Shelby Foote states that the Civil War  made us a country by uniting North and South.  He argues that before the War, its citizens might say the United States are a good place to live, noting the feeling of separation. He points out that before the Civil War, most people had never traveled more than 30 miles from where they were born and therefore had only a theoretical notion of the US as a country. During the War, millions of men and women had walked its fields and hills and cast their eyes on her valleys. They came home with a solid feeling for what this great land is. So, today, everyone, North and South, would say the United States is a good place to live.    

If the Civil War united us North and South, gold united us East and West. Shortly after the Louisiana Purchase  in 1803, President Thomas Jefferson commented that it would take 25 generations (a little more than 500 years) to settle the West.  Most of us today would balk at this estimate, yet in 1803 it was very reasonable.  Consider that by 1803, the US had been settled for 200 years and the vast majority of people lived with a few hundred miles of the Eastern seacoast.   Yet by 1850 California had become a state and twenty years later the country was united East and West by the transcontinental railroad .  The sole driving force for these amazing events was gold. Gold was discovered in 1848 at Sutter’s Mill and within months the California gold rush  had begun.  By 1855 more than 300,000 people had come to California from all over the world.  It was the biggest gold find in the world up to that date, but, to put it in perspective, only 750 metric tons (MT) of gold were mined in 10 years of this Gold rush.  All of this gold would only be a cube only 3.4 meters (11.1 feet) on a side. This fascinating story is documented in The West, another documentary produced by the prolific Ken Burns.  

Today over 2,000 MT of gold are mined each year, worldwide.  Modern mechanized and automated mining techniques enable this tremendous increase.  About 75 percent of all of the gold mined in the world has been mined in the last 100 years or so.

Today, about 50% of gold is used for jewelry, 40% for investments, and 10 % for industrial uses.  Gold has one of the best surface electrical conductivities of any metal, making it a top choice for high-performance electrical contacts.  Its resistance to corrosion enables gold solders to be very robust in harsh environments.  Gold’s malleability and ductility also make it ideal for bonding wires  in semiconductor packages.  Gold is so ductile that a 0.5mm diameter ball can be pounded out into 0.5 square meters of gold leaf (see the image).  In electronics assembly, gold is used in Electroless Nickel Gold (ENIG) surface finishes for PWB pads and some corrosion resistant, mechanically-strong solders.  Some gold solders have tensile strengths seven times greater than SAC305.  With their 280C liquidus temperature, these robust solders can also be used in high temperature applications.

But remember, without the California Gold Rush of 1849, and the Alaskan Gold Rush of 1897, the United States would be a dramatically different country today  indeed.


Dr. Ron


Image source.