| Title |
Research Papers / Welding & Joining : A Study on the Fabrication of Fluxless Solder Bump Flip Chip Package by using Ar and H2 Gas Mixture Plasma Reflow |
| Authors |
홍순민(Soon Min Hong),강춘식(Choon Sik Kang),정재필(Jae Pil Jung) |
| ISSN |
1738-8228(ISSN), 2288-8241(eISSN) |
| Abstract |
A fluxless reflow process for solder bump flip chip package was attempted to protect environment using Ar+10%H_2 plasma. The 100 ㎛-diameter Sn-3.5 mass%Ag solder balls were bonded to 250 ㎛ pitch Cu/Ni under bump metallurgy (UBM) pads by laser ball bonding method. Then, Sn-3.5Ag solder balls were reflowed in Ar+H_2 plasma. The plasma reflow time and power conditions to show the optimum bump shear strength and shape were 40s at 100 W and 20s at 200 W. During plasma reflow, the solder bump reshaped and the crater on the top of bump disappeared. The bump shear strength increased as the Ni_3Sn_4 intetmetallic compounds formed in the initial reflow stage but began to degrease as coarse Cu-Ni-Sn ternary intermetallic compounds formed at the solder/UBM interface. As the plasma reflow time increased, the fracture mode changed from ductile fracture within the solder to the fracture at the solder/UBM interface. The off-centered bumps self-aligned to patterned UBM pads during plasma reflow. |