ニッケルめっきの皮膜形態におよぼす直接無電解ニッケルめっき法の影響

Abstract

Electroless nickel plating has been extensively applied on copper circuits as an under-layer deposition for solder joints, since it is possible to deposit on the isolated patterns without an outer electrode. A palladium catalyst is generally used for the electroless nickel plating reaction on the copper patterns, because copper has a lack of catalytic activity for initiation of the deposition reaction. The electroless nickel plating is applied on the condensed copper patterns by using the palladium catalyst ; however, nickel deposits tend to occur on the resin surface due to the adsorption of palladium ions on it.Dimethylamine-borane (DMAB) has a feature of catalytic activation power on the copper. Therefore we applied dilute nickel plating solution containing DMAB as an initiator for electroless nickel deposition on the copper surface instead of applying the palladium catalyst. Selective nickel plating on the copper patterns without deposition on the resin substrate was achieved using a dilute nickel plating bath containing DMAB. In addition, the strength of solder joints was improved by introducing this process. In this way, nodules on the nickel surface were greatly suppressed, and strong joints between the solder and deposited nickel were achieved.