Research Of Electronics Components Surface Mounted Technology Quality Improvement

The most important technology in modern electronics components assembly is SMT, Surface Mounted Technology, which is developed rapidly, components become more and more smaller, integration become more and more higher, equipments become more and more advanced. Zero defects are expected from printing to reflow during the whole SMT process. But it is difficult due to many factors being impact quality, like operators handling, machine performance, raw material quality issue, technology, even production line temperature and humidity. Kinds of defects would happen in SMT, especially solder ball.Fish bone diagram analyzing tool is used to dig out the root cause, covering man, machine, material, method and environment. To achieve quality expectation, following items are improved after detailed study. Modify stencil opening and reduce stencil thickness to avoid solder paste slump after printing. Design workstation to prevent cross pollution between printed circuit boards and solder paste by squeegee. Eliminate contamination caused by solder paste residue, which should be cleaned by automated stencil cleaning system. Study components physical scale, adjust part data at placement station, solve the problem that solder paste is squeezed from pad. For reflow process, recommend the profile avoiding solder ball. Monitoring on-line humidity, control it within specification under 60%. After experiments and qualification run, it is proved that all above changes and improvements are effective, the defects of solder ball are reduced 85%, from 11714DPMO to 1803DPMO. Meanwhile, to guarantee the process quality stable, X bar R chart and C chart are implemented at printing and after-reflow inspection stations as real-time monitoring.