Wire bonding
| Wire bonding | |
|---|---|
 | |
| Technology Details | |
| Other Names | %other names and abbreviations, separated by commas% |
| Technology | Technology |
| Equipment | List of Wire bonding equipment |
| Materials | %Optional materials processed% |
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.
Contents
Equipment
The LNF has two wire bonders.
MPP iBond 5000 Wedge Bonder
The MPP iBond 5000 Wedge Bonder is designed to connect bond pads on a device 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. The Wedge Bonder offers control of individual bond parameters and programmable loop formation.
MPP iBond 5000 Ball Bonder
The MPP iBond 5000 Ball Bonder designed to connect bond pads on a device 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. Single point TAB, ball bumping, and coining, together with standard ball bonding, offer process flexibility and versatile capabilities. TAB and coining require a special tool.
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.
- All metal surfaces must be clean. There may not be any contamination such as oils, glue or corrosion.
- 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 or Package Size
- The device or package must be thin enough to fit under the workholder clamps.
- 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.
- The device to be bonded must be mounted on a solid surface using a hard material. For example, mounting with soft tape will reduce the effectiveness of the ultrasonic energy. If the device is large enough to be placed directly on the workholder, no special mounting is necessary.
Figures of merit
Bond strength
Resistivity
Parameters
The Force, Time, and Power controls are set for the best bond quality.
Force
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]
Time
The duration of the applied ultrasonic energy (Power) and bond force
Increasing the bond time basically increases the effect of the ultrasonic power.
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.
Applications
Wire bonding is intended to create electrical interconnections in semiconductor chip packaging.
Materials
Wire bonding is best done with Gold and Aluminum pads. Other materials can be use also.
Complete tool list
See also
Other related wiki pages
References
- ↑ HYBOND, Inc. - About Wire Bonding[1]
- ↑ Effects of bonding force on contact pressure and frictional energy in wire bonding by Yong Ding,Jang-Kyo Kim,Pin Tong [2]
- ↑ 3.0 3.1 EVALUATION OF WIRE BONDING PERFORMANCE, PROCESS CONDITIONS, AND METALLURGICAL INTEGRITY OF CHIP ON BOARD WIRE BONDS Daniel T. Rooney, Ph.D., DeePak Nager, David Geiger, and Dongkai Shanguan, Ph.D. [3]
Further reading
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