Page 34 - Wire Bonding in Microelectronics

CHAPTER 2

Ultrasonic Bonding

Systems and

Technologies,

Including a

Description of the

Ultrasonic Wire

Bonding Mechanism

2.1 Introduction
Currently (2008), the interconnections to >90% of integrated circuit
(IC) and other semiconductor chips are ultrasonically welded in some
manner. The exception being the devices that have solder bumps, or
other variations of flip chips (C4), as well as a few thermode-bonded
TAB devices (see Fig. 2-20). Aluminum-to-aluminum cold ultrasonic
(US) welds are usually made with Al, 1% Si wire (25–50 µm in diam-
eter) to various Al alloy (1% Si, 1–2% Cu, etc.) bonding pads on
semiconductor chips, or often Ni-Au, Pd, etc. on the package. Larger
diameter Al wire (up to ~0.75 mm, usually supplied in the fully
annealed condition) is used to interconnect power devices that may
require many amperes of current. Aluminum ribbon wire is gaining
acceptance for very high-current interconnections, and major manu-
facturers of large wire bonders offer ribbon capabilities (see Sec. 2.7.1).
However, Au-ball thermosonic bonding is used for the overwhelming

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