Author: DONALD C. BURR Company: GENERAL DYNAMICS INFO SYS Date Published: 8/23/1998
Surface Mount International
Abstract: Solder paste printing has always been considered more of an art than a science, probably because there are so many variables which must be controlled to maintain a uniform, consistent process. Of all the SMT process factors involved in creating a defect-free reflowed solder joint, paste printing is undoubtedly the single most important factor. As someone once said, “The solder joint was formed before you ever got to the reflow oven”. To ensure reliable solder joints, paste printing parameters must be measured and tightly monitored. Solder paste printing is now commonly accepted as the critical process step in surface mount assembly for controlling the quality of finished solder joints. But despite our technical advances, solder paste printing is still considered a “black art”. Richard Clothier from AMTX once noted that there are 39 variables in the solder paste printing process’ . We are still trying to understand the innerrelationships among all of these variables. The focus of this paper is to provide the user with some guidelines to use as a starting point for developing their Ball Grid Array and Chip Scale Package assembly processes.