Wet Cu passivation for high throughput fluxless Thermal Compression Bonding of Cu-Sn μbumps for Die-to-Wafer stacking

In this paper we demonstrate the application of a formulated wet passivation on scaled Cu micro-bumps before Thermal Compression Bonding (TCB)process for 3D stacked-IC (3D-SIC) applications. A formulated developmental prototype chemistry from MEC Co. Ltd is applied to protect the copper (Cu) micro-bumps from oxidation during shelf life and to provide an oxide free surface for TCB and to enable solder wetting. Good solder joint and IMC formation and almost 100% electrical yield for 20μm pitch daisy chains without yield loss in reliability tests could be obtained through the application of this formulated passivating coating on these scaled Cu bumps. Furthermore, the compatible with commercial underfill (UF) material is demonstrated with no voiding and very good UF coverage observed in between 20, 10, 7 and 5um pitch micro-bumps.