Autocatalytic cobalt is proposed as a barrier metallization for copper in lead-free soldering. Results about solder reaction and diffusion of autocatalytic cobalt with Sn-Ag-Cu and Sn-Pb alloys are presented. Bonding and solderability of autocatalytic cobalt are discussed. Solder reaction of autocatalytic cobalt with eutectic tin-lead and tin-silver-copper alloys is characterized by the formation of an homogeneous interface with thin interdiffusion layer. A thick interdiffusion layer is observed between NiP and solder alloy, with formation of brittle intermetallic compounds, mainly Ni{sub}3Sn{sub}4 and Ni{sub}3P. The formation of a very thin interlayer was observed in the case of the cobalt finish, showing a much lower cobalt and tin interdiffusion. The Au layer has a minor role on the soldering behavior of Ni and Co with Sn. Similar results are obtained with BGA balling. The contact angle of Sn-Pb and Sn-Ag-Cu on CoP/Au after soldering was about 5° in the two cases, while those for SnPb and SnAgCu on NiP/Au were about 5° and 15° respectively. Wetting time is lower for CoP than for NiP for both solder alloys.
展开▼
