Printed Wiring Board Solder Thickness Capabilities and Assembly Performance

The study first examines the solder thickness requirements for several surface mount assembly operations. Bottom side, wave solder, surface mount assembly is of special interest. Chip carrier assembly is discussed as well. Attention is paid to both placement and soldering issues. These requirements are then compared to the present capabilities of several of the PWB solder coating technologies presently available, of special interest is the Hot Air Solder Leveling (HASL) process presently being used in the PWB industry. A comparison is made of the solder coatings applied by several HASL processes. In most cases, it has been found that the thickness distributions include a statistical tail in which the solder thickness is at least marginal. Finally, thickness data is discussed of a novel solder coating process recently developed by AT&T which minimizes this effect.