Page 22 - Wire Bonding in Microelectronics

CHAPTER 1

The Technical

Introduction to the

Third Edition

urrently (2008), there are over 8 to 9 billion wires bonded per
year on the planet. Most were used in the 160 billion ICs pro-
Cduced, but many more are in interconnect transistors, LEDs,
etc. The number of wires (with two bonds on each wire) has increased
every year, including recessions to the present, from two or three
bonds in 1947 (see Fig. 1-1). The infrastructure is so extensive that no
other chip-interconnection method can displace wire bonds in the
foreseeable future, although other technologies, particularly flip chip
and its variations, are growing at a faster rate. The industry is driving
wire-bonding technology toward: (1) increased yields (< 25 ppm
defects) (see Chap. 9), (2) decreased pitch (approaching 20 µm for
both wedge and ball bonds), and (3) lowest possible and ever decreas-
ing cost. However, many new specific technical and material issues
will be involved in achieving these goals. Some examples are new
bond-pad metals (e.g., palladium, see Chap. 5; various Ni-based
metallizations, see Chap. 6), higher-frequency ultrasonic energy
(how high, how to optimize and for what materials, see Chap. 2), the
lack of quantitative understanding of the ultrasonic bonding mecha-
nism, the reality of real-time bond monitoring, as well as continuing
new failure modes resulting from wafer fabrication (e.g., bond pad
lift-up), and reliability problems in new plastic molding compounds
(e.g., “green” mold compounds), as well as increasing wire-sweep
problems (potential solution Cu ball bonding?). The above issues
result in an expanding, but technically challenging future for this
method of chip interconnection.
Some of the history and references of early wire bonding develop-
ment are given in Sec. 2.5. Also, the bonding machine components,
such as the transducer and bonding tools, are described in that
section, along with a description of the ultrasonic-bonding mechanism.

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