Advanced electronics has caused PCBs and manufacturing methods to evolve. One important requirement is high-density mounting. HASL exhibits poor thickness distribution and cannot meet the demands of high-density mounting.
The emphasis on environmentally favored products has also advanced the elimination of lead. OSP formulations are not able to prevent copper oxidation under high temperature, lead-free assembly conditions Uyemura's RGA Immersion Silver was developed to meet those challenges.
Presa RGA-14 Immersion silver directly displaces copper in an immersion reaction. RGA-14 is a high-productivity process, compatible with horizontal conveyorized equipment.
The RGA Immersion Silver deposit is uniform and meets thickness distribution criteria. It provides an ideal soldering surface under eutectic and lead-free assembly temperatures, and, with proper packaging and storage conditions, has an excellent shelf life.
The Immersion Silver plating bath is very stable because the reaction is displacement-type. It does not decompose with UV light, and, because it is a low temperature process, will not attack the substrate or soldermask. The immersion silver deposits only on copper, and not on other areas (such as can be seen with autocatalytic baths).
Anti-tarnish for Immersion Silver
Presa MGA-29 is an anti-tarnish used on printed circuit boards following immersion silver plating. The organic coating minimizes the possibility of silver discoloration and prevents degradation caused by surface tarnishing. MGA-29 provides excellent water repellency which promotes complete drying.