Silver News
New Silver Alloy Solder Safer Than Conventional
Metal Bonds - Prevents Bacterial Buildup in Drinking Water
Pipes
By Samuel Etris, Senior Technical Consultant to The Silver
Institute
Silver-tin alloys have established a superior record of performance
for strong, ductile bonds that stand up to unlimited thermal
and physical shocks, as well as prohibiting the build up of
bacteria. Now a new silver-tin alloy with improved properties
is entering the market.
Their drawback is that they have a fairly wide melting/solidification
range of about 20 degrees. However, placing these solders
in drinking water service brought a new level of attention
to the important sanitation value of silver. The silver-containing
solders found immediate acceptance in the plumbing trade,
because they required little change in plumbing practice.
Now a new silver soldering alloy has been patented by the
U.S. Department of Energy's Ames Laboratory in Ames, Iowa.
The alloy is a mixture of silver with a small addition of
copper, and is intended for electronic, electrical and mechanical
connections. The silver content is 4.7 percent and the copper
content is 1.7 percent. The Ames tin-silver-copper alloy is
a true 'eutectic' alloy (the lowest possible solidification
temperature) providing the solder user with a single melting
point at 217 degrees C. The single melting/solidification
point is a great advantage for electronic technicians, reducing
the time spent holding the parts together during solidification.
Silver makes a substantial contribution to these soldering
materials. Having an atomic size within about l5 percent of
the size of some 16 metals, molten silver will wet all of
them and provide a tenacious bond. Further, its properties
combine to produce a bond of strength and ductility essential
to a rnanufacturer in providing reliable, long-term performance
of the product.
The Ames Laboratory began with the binary silver-tin alloy
(96.2 percent tin and 3.8 percent silver3.8 percent silver)
with it superior thermal-mechanical fatigue properties, but
with a melting point slightly too high for most commercial
solder processes. By adding 1.7 percent copper, the melting
temperature was dropped by 4 degrees C, a better working temperature
for the printed circuit assembler.
Silver News - February/March 1999
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