Wire bonding has become an important process in the semiconductor industry. It can be used to make difficult connections and wedge bonding is often used in special applications. Let’s look a little closer at the wire bonding process to get a better idea of how things work.
What is a Wire Bond?
In order to connect components in today’s world of miniaturized circuits, one cannot simply solder wires from one area to another. For one thing, there is not enough space and the process of soldering creates a great deal of heat (which may damage some sensitive components). So how are the needed connections made? A special process to bond small wires from one area to another is the most efficient way.
Thermocompression
Back in the 1950s thermocompression wedge bonding was first used. This method employs three elements to bond wires:
* Heat
* Force
* Time
A heated wire is pressed to a heated surface. In some cases, it’s not necessary to heat the wire. A great deal of pressure is applied to the wire for a specified amount of time. Friction is not required for the bond to be completed. For this method, gold wires are the best choice.
Thermosonic
In just a few short years, thermocompression methods gave way to thermosonic technique. This can be done with ball or wedge bonding. As the name implies, thermosonic is a combination of thermocompression and ultrasonic methods. During this process, a wire is pushed against the surface with low force and ultrasound (high frequency sound waves) is used to vibrate the wire very fast. This helps to finish the bonding process. In this way, very little force is required to make the bond. There are three basic types of thermosonic bonding methods:
* Ball – to begin with, a heating device called a “flame off” quickly touches a gold wire and the heat forms a ball on the end of the wire. The wire is then pressed against the first surface and then pulled back to form a loop and then pressed to the second surface.
* Stud – this method is sometimes called a bump bond and a ball is created to form a bond between two conductive materials (usually at right angles). No wire is used in the process.
* Wedge – a wedge type tool presses the wire to be bonded against a surface and it is then looped and attached to another component. Wedge bonding can be done with either aluminum or gold wire. In addition, some bonds are created without heat and utilize ultrasound for the process.
