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Wire bonding is the most common interconnect method for providing the interconnection between an integrated circuit (IC) and a printed circuit board (PCB), IC-to-IC, or PCB-to-PCB. The two main wire-bonding technologies are ball bonding and wedge bonding. Although ball bonding is faster and much more popular, wedge bonding offers advantages that are well suited for optic-electronic and power devices, where reliability and performance outweighs bonding speed. However, ribbon bonding is a form of wedge bonding where flat ribbon wire is used instead of round wire. Ribbon bonding first came into use in the defense electronics sector, where it was the first interconnection level of choice for GaAs MMICs in millimeter-wave radar. Compared with the round wire, the ribbon wire bonding results in higher reliability because of the larger cross-section at the heel of the bond. There is also less cratering with a ribbon wire because the bond force and ultrasonic are distributed over a larger area.¹ In the past few years, several published papers^2-4 have compared the mechanical properties for ball and ribbon bonding, but very few papers discussed their electrical performance.

In this article the electrical characteristics of ball and ribbon bonding (round and ribbon wires, shown in Figure 1) were compared, such as wire self-inductance, self-resonant frequency (ƒ_SR) and insertion loss (IL). In order to objectively compare these parameters, three types of wires were adopted to satisfy the same comparison conditions: 0.5 x 2 mils ribbon wire, 2 mils round wire and 0.8 mils round wire. These wires, made of the same material (gold), loop height and wirelength, were measured up to 20 GHz, to obtain their electrical properties for further comparison.

Test Method
To carry out the high-frequency measurements for round and ribbon wires, all wires were bonded on the designed test board individually and measured from DC to 20 GHz, using an Agilent E8364A network analyzer and G-S-G RF probes. These designed test patterns were fabricated on high-resistive Al₂O₃ substrate. The spacings between the first and second bond pads were chosen as 75, 60, 45 and 25 mils, for different wire length, as shown in Figure 2. Thus, through these measurements, each bonding wire can be characterized for a comprehensive high-frequency comparison.