Microwave Journal's sample issue

A CompArison study
of HigH-frequenCy
CHArACteristiCs for BAll
And riBBon Bonding

In many microwave applications above 10 GHz, ribbon wire bonding is usually used because of its high frequency and high power characteristics. In general, ribbon bonding with a rectangular-shaped wire will provide lower impedance and inductance at higher frequency than a round wire. However, these results were not reached under a fair comparison for ribbon and round wires. In this article, two objective comparisons for these two wires were compared under the same wire cross-section and surface area. Therefore, three types of bonding wires were measured up to 20 GHz individually to analyze their high-frequency characteristics of self-inductance, insertion loss (IL) and self-resonant frequency (ƒSR) with the same cross-section or surface area conditions. Based on the measurements, two wires with the same surface area provide very similar characteristics due to the skin effect. It clearly demonstrates that the surface area of bonding wire determines the current carrying ability instead of the cross-section area, and dominates the high-frequency performance of the wire.

Wire bonding is the most common in- terconnect method for providing the interconnection between an inte-
grated circuit (IC) and a printed circuit board
(PCB), IC-to-IC, or PCB-to-PCB. The two
main wire-bonding technologies are ball bond-
ing and wedge bonding. Although ball bond-
ing 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 sec-
tor, where it was the first interconnection level
of choice for GaAs MMICs in millimeter-wave
radar. Compared with the round wire, the rib-
bon 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 ul-
trasonic are distributed over a larger area.1 In
the past few years, several published papers2-4
have compared the mechanical properties for
ball and ribbon bonding, but very few papers
discussed their electrical performance.