Unconventional copper wirebond looping profile approach

In a semiconductor manufacturing process wirebonding is considered to the most key critical process steps. It is where the interconnection between the Silicon (Si) die to external package is made. On top of the first and second bond, wire looping is another challenge to consider specifically using Copper (Cu) wire. In general, Cu wire had a specific characteristic that cannot be directly compared to Au wire such as it natural natures of inherent material hardness. Looping requires a consistent and stable form for the interconnection between silicon die to the external package. Typical loop trajectory used in mass production is normal forward loop bonding due to fast and easy to control, though others may be useful as well such as the reverse bonding or even folded loop depending on the necessity or complexity of the device bonding configuration. In this paper a different approach of looping formation has been explored in order to satisfy the added process step before the package encapsulation or molding to help address some concerns of the device related to its electrical performance. Unconventional looping profile has been developed achieving the desired loop formation we called as ‘hook loop’. The hook loop formation was achieved through some loop parameter manipulation despite for the limited machine software features. The new loop form found out with higher wirepull test response as compared to the normal or conventional looping used in mass production. The break mode of failure during wirepull test observed it breaks way above the ball bond neck area which indicates a less stress incurred on the wire loop formation and robust in terms thermo-mechanical impact with low risk of ball neck cracking during reliability stress. Such loop formation may also help minimize the risk of ball-pad peeling due to a less direct vertical pulling effect on the wire as the bond in motion especially in those sensitive pad structure devices.