The Effect of Leveler in Cu Electroplating Solution on the Bump Reliability of Flip Chip Packaging

Abstract

From the previous studies [1,2], it was well known that the voids at the interface of copper (Cu) and tin-silver (Sn-Ag) severely affects the bump reliability of flip chip packaging. And it was also suggested that impurity atoms existing in electroplated Cu film accelerate those voids formation [3]. So, in this study, we investigated the impact of leveler of Cu electroplating solution on the non-metallic impurities of electroplated Cu film and the voids at the interface of Cu and Sn-Ag solder was studied. We have found that the non-metallic impurity concentration was dominantly influenced by the adsorption characteristics of leveler. Fig. 1(a) shows the non-metallic impurity concentration in the electroplated Cu films using the electroplating solution containing different leveler. We can lower the total non-metallic impurity concentration to 14.9 ppm by changing the leveler. And we confirmed that 90% of voids at the interface of Cu and Sn-Ag solder can be reduced even after high temperature storage test at 150°C for 1000 hours, as shown in Fig. 1(b). Reference [1] C.Y. Liu, K.N. Tu, T.T. Sheng, C.H. Tung, D.R. Frear, P. Elenius, J. Appl. Phys. 87, 750 (2000)[2] P.S. Teo, Y.-W. Huang, C.H. Tung, M.R. Marks, T.B. Lim, 50th Electronic Components and Technology Conference, Las Vegas, NV, USA, p. 33 (2000)[3] T. Laurila, V. Vuorinen, J.K.Kivilahti, Mater. Sci. Eng. R, 49, 1 (2005) Figure 1