Wire Bonding and Ball Bonding

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Wire Bonding- Wire bonding is the method of making interconnections (ATJ) between an integrated circuit (IC) or other semiconductor device and its packaging during semiconductor device fabrication. Although less common, wire bonding can be used to connect an IC to other electronics or to connect from one printed circuit board (PCB) to another. Wire bonding is generally considered the most cost-effective and flexible interconnect technology and is used to assemble the vast majority of semiconductor packages. Wire bonding can be used at frequencies above 100 GHz.

Bond Wires usually consist of one of the following materials

• Gold
• Copper
• Aluminium
• Silver

Copper wire has become one of the preferred materials for wire bonding interconnects in many semiconductor and microelectronic applications. Copper is used for fine wire ball bonding in sizes from 0.0004 inch (10 micrometres) up to 0.004 inch (100 micrometres) Copper wire has the ability of being used at smaller diameters providing the same performance as gold without the high material cost.

The main classes of wire bonding are as follows

• Ball Bonding
• Wedge Bonding
• Compliant Bonding

1. Ball Bonding- Ball bonding is a type of wire bonding, and is the most common way to make the electrical interconnections between a chip and the outside world as part of semiconductor device fabrication. Gold or copper wire can be used, though gold is more common because its oxide is not as problematic in making a weld. Ball bonding usually is restricted to gold and copper wire and usually requires heat. Ball bonding are limited to small diameter wires, suitable for interconnect application. In either type of wire bonding, the wire is attached at both ends using a combination of downward pressure, ultrasonic energy, and in some cases heat, to make a weld. Heat is used to make the metal softer. The correct combination of temperature and ultrasonic energy is used in order to maximize the reliability and strength of a wire bond. If heat and ultrasonic energy is used, the process is called thermo sonic bonding.
2. Wedge Bonding- In wedge bonding, the wire must be drawn in a straight line according to the first bond. This slows down the process due to time needed for tool alignment. Ball bonding, however, creates its first bond in a ball shape with the wire sticking out at the top, having no directional preference. Thus, the wire can be drawn in any direction, making it a faster process. In wedge bonding, the wire must be drawn in a straight line according to the first bond. This slows down the process due to time needed for tool alignment. Ball bonding, however, creates its first bond in a ball shape with the wire sticking out at the top, having no directional preference. Thus, the wire can be drawn in any direction, making it a faster process.
3. Compliant Bonding- Compliant bonding transmits heat and pressure through a compliant or indent able aluminium tape and therefore is applicable in bonding gold wires and the beam leads that have been electroformed to the silicon integrated circuit (known as the beam leaded integrated circuit).