Characterization of a novel fluxless surface preparation process for die interconnect bonding

For applications such as 3D integration, flip chip, and other die interconnection processes, a variety of metals is used to form an electrical and mechanical bond between the two components. Native oxides, however, quickly form on many of the common bond materials, hindering the integrity of the joint and adversely affecting long-term reliability. A new method has been developed to reduce these surface oxides and passivate the exposed metal surfaces against re-oxidation. Avoiding the use of acids or the possible exposure to hot electrons, ions and highly energetic atoms of conventional vacuum plasma, the developed and tested processing is carried out in atmospheric ambient to remove native oxides from solders and contact metals, enabling consistent bonding at modest temperatures and bond forces. The processing approach has been applied to a variety of metal and alloy surfaces, with bonding pursued over a range of forces and temperatures. Analysis of treated and untreated surfaces will also be presented, including SEM images and surface analysis techniques such as laser ellipsometry. Finally, physical bonding results will demonstrate the efficacy of the proposed atmospheric surface preparation approach, lowering the temperatures and bond forces required to achieve effective joining between component parts.