Although wire bonding is an essential process in the development of virtually all semiconductors, specifically with interconnects, it is a relatively new technology. Choosing the right company for the process is critical to ensure that the interconnects are completed accurately and to your desired specifications.
This process first appeared in the 1960s developed by Alexander Coucoulas, an American who was a research engineer and an inventor. He is credited with developing thermosonic bonding, or the use of heat, pressure and ultrasonic vibrations to create bonds on various types of substrates.
Initially, the process was used to attach the lead wire to glass substrates and the silicon integrated circuit chips used in different early computers. It originally used processes used only ultrasonic vibrations and pressure, but this created unacceptably high levels of cracks and damage to the glass and the chips. To correct this issue, heat was added to allow for less pressure and lower levels of ultrasonic vibrations.
Today, using advanced equipment and technology, wire bonding can be completed on a much wider variety of different components and substrates. Different options in bondwires including gold, silver, copper and aluminum allow for various heat levels combined with pressure and ultrasonic vibrations.
The technicians setting up the process still have the challenge of selecting the right configurations based on the substrate, the chip component and the bondwire. Copper is often used in semiconductors as the bondwire because it can be effective as a very fine bondwire and also has an overall lower cost of production than other bondwire options.
While copper bondwire is the lower cost option, there are still many components that require the use of gold bondwire. This is a wire that has a 99.99% purity. There are also gold alloy wires that boost the bondwire strength and increase the durability and longevity of the component.
Issues to Consider
In addition to the specific bondwire used for wire bonding of a microelectronic component or the semiconductor, there are other challenges that have to be carefully considered.
The correct bonding tool, which is used in ball bonding, has to be selected to have the right design and tip shape to suit the specific bonding requirement. A fine-pitch ball bonding process is very flat to the surface, which is often essential in microelectronic components and semiconductors where even a slightly raised surface can be a very serious issue.
Other issues to consider include the length of the bondwire that is affected during the heating process and if the application of the heat changes the wire and creates weak spots or area. This turn can impact the loop height of the wire, which needs to be carefully matched to the component specifications.