Study on Cu-pillar Interconnect for Flip-Chip-on-Module Packages-(PPT)

摘要

Two interconnect systems of Ni/Au- and Sn-capped copper pillar joint with lead-free Sn-Ag-Cu alloys and Cu/Ni/Au electrodes are evaluated for flip-chip-on-module (FCOM) packages. These systems can help increase the packaging density due to the use of fine-pitch Cu-pillar bumps and greatly improve the packaging performance thanks to high thermal and electrical conductivity of copper as interconnect. It may also enhance the FCOM packaging reliability due to improvement of solderability by using lead-free Sn-Ag-Cu (SAC) alloys as the binder for Cu-pillar bumps on a device and Cu/Ni/Au electrode on a PCB module. Sn-capped and Ni/Au-capped Cu-pillar joint with SAC alloys demonstrate different interconnecting mechanism. The tin finish will be dissolved into SAC alloys and result in direct contact between Cu-pillar and SAC alloys while the Ni/Au finish will remain to prevent the copper diffusion from Cu-pillar bumps. The partial Ni finish is involved in the formation of (Cu, Ni){sub}6Sn{sub}5 in Ni/Au-capped system. In Ni/Au-capped FCOM packages, Cu{sub}6Sn{sub}5 IMC is very stable and will not thicken under multiple reflow and all reliability tests and thus more efficiently prevent the copper pillar diffusion.