The Challenges of Fine Pitch Copper Wire Bonding in BGA packages

Copper wire technology is not new to the semiconductor industry especially for midrange I/O packages such as SOIC and PDIP, which require thicker wire diameter. Today, copper wire bonding has seen increasing demand for higher quality and lower cost packaging. In recent years, a few companies have started development work in high pin count packages especially for BGA packages, which require smaller wire diameter (lmil and below). Freescale is one company that has been aggressively pursuing further developments. Development and optimisation of robust fine pitch copper wire bonding processes for BGA packages requires an assessment of Cu-Al inter-metallic growth after isothermal ageing. This paper specifically discusses the material requirements, capillary selection, and some characteristics of the Cu-Al system, as well as a comparison to Au-Al system. The challenges of copper wire bonding in different bond pad thickness and metallization are also briefly discussed.