An experimental study on organic solderability preservative

Organic solderability preservatives (OSP) are regarded as an excellent pad finish for fine pitch SMT because they can produce a very thin and even coating. However, OSP coatings are more vulnerable to the thermal, humidity and physical effects compared to the HASL coating. In this study, a designed experiment was carried out to systematically study the effects of seven factors on solderability of OSP coated PCBs. These factors included PCB handling, shelf life, prebake atmosphere, dry temperature during cleaning, time delay between cleaning of the first-side misprint and re-print, and hold time between soldering operations. The results of analyzing the experiment data have shown that hold time between soldering operations is the most significant factor; prebake atmosphere when prebake is necessary, bare PCB handling, and dry temperature during cleaning of the first-side misprint are also significant; and within their selected ranges used in the experiment, shelf life, time delay between cleaning of the first-side misprint and re-print, and dry temperature during cleaning after one reflow are not significant. The effect of the water solvent used in the aqueous cleaner on the removal of the OSP coating was also quantified by an additional experiment.