Development and commercialization of solder bump fabrication technology with molten solder injection method

Abstract

Fine pitch interconnection using a fip-chip method is a key technology to achieve ultra-high density packaging on 2.1D/2.5D/3D integrated devices. As the solder bump size gets smaller for fne pitch applications, controlling the properties of solder joints becomes more important for chip package interaction (CPI) and electro-migration (EM) performance. The electro-plating method is widely used to fabricate fne pitch bumps; however solder compositions are limited to pure Sn or some binary solders such as Sn-Ag, Sn-Cu, etc. Hence, a bumping technology with fne pitch capability and solder alloy fexibility is needed. Injection Molded Solder (IMS) is an advanced solder bumping technology for use on wafer and laminate. IMS is a very simple technology, and solder bumps can be formed by the injection of molten solder into holes of resist material. Therefore, solder alloys can be fexibly selected, and there is a high capability of fne pitch applications. We fabricated a prototype tool to develop IMS bumping technology on wafers. In parallel, we developed the high thermal durability resist material because the resist material must be stable at high temperatures (around 250 degrees C) during the IMS process and be perfectly stripped after the IMS operation without any residue on the surface of wafers. We successfully demonstrated fne pitch solder bumping down to 40 μm pitch and 20 μm in diameter with Sn-3wt%Ag-0.5wt%Cu using the prototype tool and developed resist material. In this paper, we introduce the IMS technology and development activities toward the commercialization of this technology.