| 초록 |
While tin-lead (Sn-Pb) alloys for soldering of chips and connectors on printed circuit board (PCB) have been mainly used due to its low soldering temperature, recently, the usage of those in electronic devices is strongly restricted by governments because the heavy elements such as Pb, Cr, Cd, Hg, and Cr6+cause environmental contamination on soil and mankind, etc. Accordingly, Au, pure Sn, and ternary alloys of Sn have been largely studied and to be the major candidates for the replacement of Sn-Pb layers on Cu-alloyed base material. The increased melting temperature from 183℃ to 232℃ by changing coated layers from Pb-Sn ( 73.9 at.%) to pure Sn resulted in severe surface oxidation of Sn which degrades solderbility during reflow process at increased temperature. To prevent the oxidation of Sn during high temperature reflow process, the effects of microstructure of Sn, passivation layer on Sn layer, and process conditions of underlayer Ni have been investigated. We suggest that both the addition of light element on underlayer Ni during electroplating and the passive layer formation on Sn surface are the superior method to overcome the surface oxidation of Sn during reflow process at 260℃ for 120 sec. |
