Lead‐Free Surface Mount Technology

Surface mount technology (SMT) involves the assembly or attachment of surface mount devices onto the printed circuit board. This chapter reviews the surface mount process for lead-free soldering, including printing, component placement, reflow, inspection, and test. It discusses some advanced miniaturization technologies used in the SMT process. SnAgCu materials with 3.0-4.0% Ag and 0.5-0.9% Cu and remainder Sn are widely accepted as lead-free solder paste alloys within the industry. The solder paste process must accurately deposit the correct amount of solder paste onto each of the pads to be soldered. Screen-printing the solder paste through a foil or stencil is the most commonly used technique. Vacuum soldering helps to eliminate or minimize voiding to a few percent. Hydrogen atmosphere is also used. Robotic soldering is a soldering method which uses robots to solder surface mount or pin through hole components onto the printed circuit board.