High Phosphorous Electroless Nickel Process for Mobile Phone PWBs

摘要

An Electroless Nickel and Immersion Gold (ENIG) plating process with a middle phosphorous content nickel layer isrncurrently a mainstream final finishing application for mobile phone Printed Wiring Boards (PWB). As a trend according tornthe worldwide market growth of mobile phones, the demand for higher resistance characteristics in corrosive environmentsrnfor ENIG finished boards has increased. Although various methods have been introduced as an evaluation method for higherrncorrosion resistance, sulfurous acid gas (SO_2 gas) testing is a recent area of industry focus. However, because of thernsignificant corrosive characteristic of SO_2 gas, the conventional ENIG layer cannot tolerate this testing method, and thus hasrnbecome an area of major concern. As a result, a high phosphorous nickel ENIG plating process, which inhibits higherrnresistance in a corrosive environment compared to a middle phosphorous process, is being adopted as a final finishingrnmethod. However, several other factors of the total plating process that may influence corrosion resistance have not beenrnverified or fully investigated. Therefore, in this study we introduce ENIG plating layer characteristics required for higherrnresistance in corrosive environments by investigating corrosion conditions of ENIG layers caused by SO_2 gas testing, andrnfurthermore conduct observations on factors that influence these ENIG characteristics.