Automatic wedge bonding with ribbon wire for high frequency applications

Abstract

Wedge bonded ribbon wire has demonstrated the ability to provide better performance than round wire in many high performance devices. The commercial marketplace for microwave and optical devices that operate at very high frequency has grown to the extent that high quality, high volume ribbon wire bonding processes have become a necessity. When a high frequency electrical signal is carried on a wire, the signal travels along the thin layer near the surface. This is called the skin effect. Due to the skin effect, the same cross section ribbon wire has much higher current carrying capability than round wire. Ribbon wire also has smaller effective inductance and less signal cross talk than round wire. In addition to superior electrical attributes, ribbon wire also provides wire bonding process benefits, such as very low loops and better looping control due its resistance to sway and sagging. The bond force required to bond ribbons is much lower than that for round wire because, in a sense, the ribbon is pre-deformed so the geometry of its contact area more closely matches that of the device surface. This paper reviews the many performance benefits ribbon wire can provide, and examines the market and process requirements of ribbon wire bonding. It shows how optimal bonding results are achieved through process optimization and Design of Experiments (DOE) and reviews typical bonding and assembly challenges for common high-frequency packages. Test methodologies to identify the optimal wedge bonding tool configuration and ribbon composition also are summarized, including DOE and statistical analyses for fine ribbon wires [13 pm x 51 pm (0.5 x 2 mil)] and heavy ribbon wires [25.4 μm x 254 μm (1 x 10 mil)]. Results from these tests are presented as guidelines for determining process capability in production applications.