University Technology    of Malaysia

 WHAT IS WIRE BONDING ?
Microelectronic a§§igment

Name :                    Mohd Fahmi Bin Abdul Hamid              Mohd Fhaizal Bin Radzi

Lecturer :                Prof.Madya.Salwani Bt.Mohd Daud

Course/section :    3DDE/74

Content :               

Wirebonding is an electrical interconnection technique using thin wire and a combination of heat, pressure and/or ultrasonic energy. Wirebonding is a solid phase welding process, where the two metallic materials (wire and pad surface) are brought into intimate contact. Once the surfaces are in intimate contact, electron sharing or interdiffusion of atoms takes place, resulting in the formation of wirebond. In wirebonding process, bonding force can lead to material deformation, breaking up contamination layer and smoothing out surface asperity, which can be enhanced by the application of ultrasonic energy. Heat can accelerate Interatomic diffusion, thus the bond formation.

 History and applications

Wirebonding is the earliest technique of device assembly, whose first result was published by Bell Laboratories in 1957. Sine then, the technique has been extremely developed:

Fully automatic machines have been developed for volume production.

Bonding parameters can be precisely controlled; mechanical properties of wires can be highly reproduced.

Bonding speed can reach 100-125 ms per each wire interconnection (two welds and a wire loop).

Bond pitch of 50 mm and the consistent loop with less than 40 mm have been achieved.

Most reliability problems can be eliminated with properly controlled and much improved tools (capillaries and wedges) and processes.

Specific bonding tools and wires can be selected by packaging engineers to meet the requirements.

Infrastructure of the technique has been comprised by large wirebonding knowledge, manufacturing people, equipment venders and materials.

As a result, a reliable and completely repeatable bond formation process can be produced.

Owing to its potentially low cost, its much improved yields and reliability, wirebonding, as the dominant chip-connection technology, has been used with all styles of microelectronic packages, from small individual chip packages to large, high-density multichip modules. The most popular applications that use wirebonding are:

Single and multitiered cofired ceramic and plastic ball grid arrays (BGAs), single chip and multichip

Ceramic and plastic quad flat packages (CerQuads and PQFPs)

Chip scale packages (CSPs)

Chip on board (COB)

Figure A3. Chip interconnection using wirebonding technology (after Ericsson Microwave System AB).

Virtually all dynamic random access memory (DRAM) chips and most commodity chips in plastic packages are assembled by wirebonding. About 1.2-1.4 trillion wire interconnections are produced annually. Manufacturing losses and test failures are about 40-1000 ppm and trending downward each year. It is believed that wirebonding will continue to dominate memory and commodity packaging requiring relatively small I/O counts (< 500 I/O) in the future. In addition, wirebonding method is used to connect other components, such as resistors or capacitors, to substrate, package terminals to substrate, or one substrate to another.

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