Wire bonding

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Wire bonding
Technology Details
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Technology Technology
Equipment List of Wire bonding equipment
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Wire bonding can connect bond pads on devices to the leads of a package such as DIP or TO-5 cases. It can also be used to interconnect bond pads between two devices, the same device or to a printed circuit board.

Method of operation

Ultrasonic energy, when applied to metal to be bonded, renders it temporarily soft and plastic. This causes the metal to flow under pressure. The acoustic energy frees molecules and dislocates them from their pinned positions which allows the metal to flow under the low compressive forces of the bond.

The friction of the wire breaks up and sweeps aside some contaminants in the weld area exposing clean metallic surfaces which promote the metallurgical bonds. It is important, however, to begin with a clean surface to avoid difficulties or failures in bonding. In some cases the ultrasonic scrubbing may not be able to remove contaminants as in the case of lubricants. [1]

Design considerations

  • Wire material/bond pad material
    • Gold or Aluminum pads provide the most reliable bonds. Platinum and Copper can also be bonded.
  • Bond pad arrangement
    • Bond pads should be at least 75 µm square to make is easier to place the bond. Larger pads are better. Bond size should not exceed 75% of the bond pad size.
  • Bond pad thickness
    • A minimum of 0.76 micron of soft gold on an interface material such as 5 micron nickel works well for bondability and to minimize pad damage. Thicker is better. There has been limited success with thinner layers.
    • For aluminum, .8 micron pad thickness is recommended, 3 micron for higher reliability.
  • Metal adhesion
    • Metal adhesion must be good to prevent lifting of the pad metal at the bond point.
  • Wafer or Package Size
    • A heated workholder is available capable of holding up to approximately 2.25" (57mm) square or 2.25" (57mm) diameter wafers. It can also hold most DIP packages with .1" lead spacing.
    • A heated workholder is available capable holding two TO-5 packages.
  • Wafer thickness
    • The device or package must be thin enough to fit under the workholder clamps.
  • Bond Pads

Figures of merit

Bond strength



The Force, Time, and Power controls are set for the best bond quality.


The amount of additional pressure applied during the bond cycle.
Increasing force generally improves bondability, but too high a bond force may impair the efficiency of ultrasonic energy transfer (power). [2] Excessive bond deformation can occur if either the device being bonded is not properly secured or if the bond force applied to the bonding tool is too light. You may need to increase the force when you increase power. [3]


The duration of the applied ultrasonic energy (Power) and bond force
Increasing the bond time basically increases the effect of the ultrasonic power.


The amount of ultrasonic energy applied during the bond cycle
Increasing the Power setting tends to increase the bond strength, but too much power will weaken the wire at its junction to the bond pad. The width and quality of the bond can be used to set the Power control.

Insufficient power can result in narrow, under formed bonds and tail lifts. Excessive power results in wire bonds with a “squashed’ appearance, heel cracks, cratering damage to the semiconductor die, undesirable build-up of residual bond pad metallization on the bonding tool, and poor mechanical integrity of the wire bonds. [3]

Workholder Temperature

Heat applied to the sample during bonding. This is most useful for Gold and Platinum. Typical temperatures range from 100° to 160° C.
Increasing temperature increases the effects of the force and power parameters.
With gold wire, the ultrasonic power may be eliminated.

Wedge heater Temperature

Heat is applied to the wedge when the workholder is heated. When used, the wedge heater is normally set to 36.


Wire bonding is intended to create electrical interconnections in semiconductor chip packaging.


Wire bonding is best done with Gold and Aluminum pads. Other materials can be use also.


The LNF has one wire bonder.

Wire Bonder

Main article: Wire Bonder

The K&S 4123 Wire Bonder is a wedge bonder that is designed to connect bond pads on devices to the leads of a package such as DIP or TO-5 cases. It can also be used to interconnect bond pads between two devices, the same device or to a printed circuit board.

Complete tool list

Main article: Wire Bonder

See also

Other related wiki pages


  1. HYBOND, Inc. - About Wire Bonding[1]
  2. Effects of bonding force on contact pressure and frictional energy in wire bonding by Yong Ding,Jang-Kyo Kim,Pin Tong [2]

Further reading

  • Other stuff, e.g. technology workshop slides
  • External links (can be in another section below, if appropriate)