- There are basically two forms of wire bonds, Wedge bonds and Ball bonds. Recent industry survey shows that about 90% of all electronic packages and assemblies are produced using ball bonds and about 10% are produced with wedge bonds. An increase in the use of ball bonding is expected as semiconductor devices increase in functionality and decrease in size causing smaller bond pads and closer bond pad spacing.
- The most widely used wire materials are Gold (Au) and Aluminum (Al) however, Silver (Ag) and Copper (Cu) are also used. Copper wire (ball bonding) has gained considerable attention due to its economic advantage and strong resistance to sweeping. Gold was the original material used when wire bonding technology was developing. Aluminum has become popular due to its good electrical performance and lower cost. Gold wire can be bonded in the shape of a wedge or a ball. Ball bonds can be used in very tight spacing. Aluminum wire can only be wedge bonded and so is limited when spacing is tight.
- There are three main methods of wire bonding: Thermocompression, Ultrsonic, and Thermosonic.
- Thermocompression bonding was extensively used until Ultrasonic bonding technology became more prevalent. Thermocompression bonding requires a high-force on a surface with a high temperature of around 300°C. It provides excellent, reliable Al-Au bonds with flexibility in the bonding direction allowed. The wire material is Au but the pad can be Au or Aluminum.
- Ultrasonic bonding is the most common bonding technology used for Al bond wires and is performed at ambient temperature. Bonding is formed as a wedge bond by pressure and vibrational energy.
- Thermosonic bonding is used for Au wires and currently comprises about 90% of all wire bonding. It is done at temperatures of around 100°C to 240°C. Bonding is formed when the ultrasonic energy combines with the capillary technique of thermocompression bonding. Occasionally, it is used for Au wedge-wedge bonding, but mostly it is best suited for a ball-wedge bond.
- The exact material and method of wire bonding will be specified by our customers. Additionally, the wire specifications are determined by the amount of current to be carried through the device as per the customer's requirements.
At MEM Hitech, this process is automatically executed by 8028 and 1488plus Wire Bonders from K&S. |
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