Converting High Volume IC Manufacturing To Cu Wire Packaging

Abstract: Converting integrated circuit (IC) bills of material (BOMs) from gold (Au) to copper (Cu) wire is becoming mainstream in semiconductor manufacturing. With the price of gold skyrocketing, cost is the primary driver for conversion. Although there are other advantages that complement the huge cost savings, few contract manufactures and Original Equipment Manufacturers (OEMs) are excited about these enhanced properties. Instead, they are most concerned with manufacturing controls, interaction with current BOMs, and the long-term reliability of Cu-wire in IC packaging. The benefits and concerns of using copper wire versus traditional gold wire BOMs are explored and various customer concerns are discussed.

A myriad of evaluations were designed to determine the impact of the Cu-wire bonding across various wafer and package technologies. This laid the groundwork for a significant ramp into production. However, market acceptance needed to be considered as well, particularly from the OEM and Electronic Manufacturing Services (EMS) point of view. There are subtle benefits, such as improved electrical and thermal properties as well as slower intermetallic growth as summarized in Figure 1 above, but the primary risks are what customers tend to focus on. These include oxidation and increased hardness of the wire itself, interactions with impurities in various mold compounds, and controlling the manufacturing process over time.

Initially traditional gold-wire bonders were retrofitted with conversions kits to allow the use of copper wire during the IC manufacturing bonding process. As more was learned about Cu-wire bonding, new bonding equipment was specifically designed to accommodate the unique requirements of using copper wire. The introduction of forming gas, capillary design, and other factors will be discussed as key parameters are optimized during the characterization of the copper-wire bond recipe. The definition of a “good bond”, revised process controls, extended reliability studies, and a look into what’s next wrap up the discussion.