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Clean Connections
| Article
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20711 |
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Section : |
NATURAL SCIENCE
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| Issue
Date : |
9 / 1992 |
3,257 Words |
| Author
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Ronald L. Iman And Larry R. Lichtenberg
Ronald L. Iman is a distinguished member of the technical
staff with the systems reliability modeling group of Sandia
National Laboratories. He is also president-elect of the
American Statistical Association. Larry R. Lichtenberg
is a member of the technical staff in the Government
Electronics Group of Motorola, Inc., in Scottsdale, Arizona |
The electronics industry is huge, and growing, because electronics technology conveniently meets so many needs of modern society. The communications industry--from telephones to television--relies on electronics technology. Computers as we know them today could not exist without electronics technology. Not could airplanes fly, nor cars drive, nor subways run. Libraries, offices, kitchens, living rooms, machine shops, and video arcades all contain a surprising number of devices relying on electronic circuitry.
Inside almost every electronic device is a circuit board to which are attached such electronic components as capacitors, resistors, transistors, and integrated circuit chips. Each year hundred of millions or electronic components are attached to millions of circuit boards. Through this attachment process, diverse components are converted to a complex, seamless system of electrically interconnected parts. The components must be attached well so that electrical current can flow readily between the circuit board and each component. The components also must be securely attached so the connection is not broken through handling, and the connection must maintain constant electrical properties over time.
Solder, a tin and lead alloy that melts at about 180 C, is the key material used in connecting components to circuit boards. The soldering process requires heat to melt the solder and heat up the two metal surfaces being connected, plus a cleaning agent (flux) to remove the oxide layer that naturally builds up on most metal surfaces. The two surfaces must be clean metal so the molten solder can form a direct metallurgical bond with each. When the molten solder cools, it acts as conductive glue, uniting the combined elements into a single, continuous electrical circuit.
The environmental problems with soldering arise because the fluxes in common use until recently leave a residue that must be cleaned off, lest the residues later become conducting and degrade the performance of the circuit. In looking for an efficient cleaning solvent, electronics manufacturers were readily drawn to chlorofluorocarbons (CFCs), which are very stable under working conditions and effective at cleaning flux residues.
Each year the electronics industry uses millions of gallons of chemical solvents, including hundreds of thousands of gallons of ozone-depleting chemicals, to clean flux residues from electronic equipment. This use accounts for as much as 20-24 percent of the worldwide consumption of CFCs. With the United States committed
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