Solder Paste Printability Tester and Method

Solder paste print property is critical to product yield in a SMT (surface mount technology) line. Investigation has shown that poor solder paste printability results in a large amount of defects. In this letter, basing on the rolling phenomenon during solder paste printing process, a novel tester was developed to measure the solder paste printability. This device offers a uniform printing condition, such as squeegee angle, printing pressure and speed, etc. to discern the different printing features among various solder pastes. The characteristic of this device is using a "squeegee-roller" printing mechanism, that is, the stencil is designed like a roller or a drum that makes it possible to perform continuous print action. During printing test, a J-shape probe was employed to pierce into the surface of the solder paste to detect the tangential force induced by the rolling of solder paste. Using this machine, two brands of SnPb and SnAgCu solder pastes were tested. It was found that the printing life of Brand A excelled that of Brand B, and the evolutions of the rolling tangential forces exhibited different characteristics between SnPb and SnAgCu solder paste, where the tangential force of SnPb solder paste rose to a maximum and then quickly it ceased to roll at a high rolling rate, but the tangential force of SnAgCu solder paste declined slowly all along. In a word, this tester has the potential to offer a quantitative and low cost evaluation on the printability of solder paste