Pb-free solder applications and requirements in automotive industry
Ford Research Laboratory
Ford Motor Company
Dearborn, MI 48121-2053
The automotive electric and electronic components encounter a harsh environment: extremes in hot and cold temperature cycling, vibration, and corrosive atmosphere, coupled with additional component self-heating. The Key Life Test of Ford Corporate Engineering Test Procedure states that the reliability of electronic modules and sensors has to meet or exceed the wear out requirements based on the real world customer usage profiles with regard to 10 years/150,000 miles in service. The test is accelerated and uses combinations of the environmental stresses of temperature, humidity, vibration, mechanical cycling/shock/drop, actual electrical loads, dust, salt, and thermal soak/cycle/shock.
One example of using Pb-free solder in automotive applications is alternator. The ambient service temperature of the alternator can get to 175oC. Ford has produced alternators with Sn-3.5Ag eutectic solder since 1988, and constitutes one of the very first Pb-free solder assemblies in mass production (5 million parts a year) in the industry. The wave soldering process has been carefully designed, due to the higher melting temperature of the Sn-Ag solder, larger thermal mass of the alternator stator, and the bare copper of the stator wires. A special no-clean, VOC-free, water-based flux was also implemented recently for further improving the environment. The flux is compatible with the Sn-Ag solder and the bare copper wires, is capable of either foaming of spraying, and with excellent solder joint quality.