Reduction of residue using various nitrogen atmospheres

摘要

Surface mount technology (SMT) demands the optimization of all resources to minimize defects and likewise maximize yields. In today's no-clean marketplace, concerns for reliability, testability, and aesthetics are key among both contract and original equipment manufacturers alike. While there may exist no-clean materials that meet the more rigorous demands of a reduced residue, these materials often require inert atmospheres during reflow to accomplish such. Often times, the oxygen levels demanded therein are difficult and/or too costly to maintain. Additionally, only a fraction of SMT product lines in a particular facility may require tighter residue controls, while the remaining do not. As a result, at least two different solder paste products are necessary to supply the full needs of the production area - one that requires nitrogen and one that does not This, of course, serves only to complicate purchasing, storage, and manufacturing. Results herein indicate that a single no-clean or RMA product exists that can be used at any oxygen level between ambient (200,000 ppm O_2) and nearly inert (2 ppm O_2), to meet specific residue level demands. The products examined here yield residue volumes proportional to the oxygen level used in convectionreflow. Additionally, it has been reported in other sources that residue levels for certain no-clean or RMA solder pastes are not significantly reduced by nitrogen reflow methods. Therefore, the benefit is, most likely, formulation specific.