ABSTRACT
The metallurgical “life cycle” of a solder joint, whether lead-free or containing Pb, has multiple stages. First, for surface mount technology, the solder alloy is atomized into powder and fabricated into a paste. For through-hole technology, the solder alloy is melted in the wave soldering pot. Second, the temperature of the solder must be sufficiently low during reflow or wave soldering to avoid damage to the board and components but high enough to melt and wet the components and the board in a reasonable processing time. Third, the solder joint must solidify without forming defects that affect the joint’s integrity, during and immediately after solidification, and during use. Next, the solder joint must be able to withstand the stresses imposed by use, including thermomechanical fatigue, thermal shock, vibration, and impact. Last, when the product is removed from service, the circuit boards with their solder joints become waste and are burned, buried, or recycled.
