Roughness evolution of Cu6Sn5 intermetallic during soldering

The roughness evolution of the Cu6Sn5 intermetallic compound during the sol dering reaction of 40/60% (by wt %) PbSn solder on Cu and its effects on we ttability were studied due to their importance in the reworking of microele ctronic components. The roughness parameters investigated were R-rms and th e ratio, R-rms/lambda(a), where R-rms is the root mean square roughness and lambda(a) is the average distance between asperities. It was found that R- rms increased with soldering time for the range of soldering times studied. The evolution of R-rms was found to follow a parabolic relation with solde ring time-which is similar to that observed for the intermetallic thickness . However, the ratio R-rms/lambda(a) was found to increase very gradually f or the range of soldering times investigated. From the ratio R-rms/lambda(a ) obtained, the average inclination of the intermetallic morphology was cal culated. The average inclination of the Cu6Sn5 intermetallic morphology was found to be greater than the apparent contact angle observed during the we tting of the 40/60% PbSn solder on Cu substrates. This inconsistency was at tributed to the difference in the roughness of the Cu6Sn5 intermetallic in the inner regions and at the reaction band at the edge of the solder cap. ( C) 1999 American Institute of Physics. [S0021-8979(99)05721-7].