Gold wire ball-bonded to a gold contact pad

Ball bonding is a type of wire bonding, and is the most common way to make the electrical interconnections between a microchip and the outside world as part of semiconductor device fabrication. Image File history File links Download high resolution version (1024x768, 88 KB) Summary Description: contact pad, ball w:wire bonding Author, date of creation: selfmade by Shaddack, 5 December 2005 Source: self-made Copyright: Public Domain (PD) Comments: From some sort of an intelligent display, gold wire on a gold... Image File history File links Download high resolution version (1024x768, 88 KB) Summary Description: contact pad, ball w:wire bonding Author, date of creation: selfmade by Shaddack, 5 December 2005 Source: self-made Copyright: Public Domain (PD) Comments: From some sort of an intelligent display, gold wire on a gold... Wire bonding is a method of making interconnections between a microchip and the outside world as part of semiconductor device fabrication. ... Nasas Glenn Research Center clean room. ...

Gold or copper wire can be used, though gold is more common because its oxide is not as problematic in making a weld. If copper wire is used, nitrogen must be used as a cover gas to prevent the copper oxides from forming during the wire bonding process. Copper is also harder than gold, which makes damage to the surface of the microchip more likely. However copper is cheaper than gold and has superior electrical properties, and so remains a compelling choice. It has been suggested that Gold Bar be merged into this article or section. ... General Name, Symbol, Number copper, Cu, 29 Chemical series transition metals Group, Period, Block 11, 4, d Appearance metallic brown Atomic mass 63. ... This article does not cite its references or sources. ...

Almost all modern ball bonding processes use a combination of heat, pressure, and ultrasonic energy to make a weld at each end of the wire. The wire used can be as small as 15µm in diameter - such that several welds could fit across the width of a human hair.

A person upon first seeing a ball bonder will usually compare its operation to that of a sewing machine. In fact there is a needle-like disposable tool called the capillary, through which the wire is fed. A high-voltage electric charge is applied to the wire. This melts the wire at the tip of the capillary. The tip of the wire forms into a ball because of the surface tension of the molten metal. A modern machine (Singer Symphonie 300) A sewing machine is a mechanical (or electromechanical) device that joins fabric using thread. ... In physics, surface tension is an effect within the surface layer of a liquid that causes the layer to behave as an elastic sheet. ...

The ball quickly solidifies, and the capillary is lowered to the surface of the microchip, which is typically heated to at least 125°C. The machine then pushes down on the capillary and applies ultrasonic energy with an attached transducer. The combined heat, pressure, and ultrasonic energy create a weld between the copper or gold ball and the surface of the microchip - which is usually copper or aluminum. This is the so-called ball bond that gives the process its name. A transducer is a device, usually electrical or electronic, that converts one type of energy to another. ... Aluminum is a soft and lightweight metal with a dull silvery appearance, due to a thin layer of oxidation that forms quickly when it is exposed to air. ...

Next the wire is passed out through the capillary and the machine moves over a few millimeters to the location that the microchip needs to be wired up to (usually called the substrate). The machine again descends to the surface, this time without making a ball so that the wire is crushed between the substrate and the tip of the capillary. This time the surface is usually gold, palladium, or silver - but the weld is made in the same way. The resulting weld is quite different in appearance from the ball bond, and is referred to as the wedge bond, tail bond, or simply as the second bond. General Name, Symbol, Number palladium, Pd, 46 Chemical series transition metals Group, Period, Block 10, 5, d Appearance silvery white metallic Atomic mass 106. ...

In the final step the machine pays out a small length of wire and tears the wire from the surface using a set of clamps. This leaves a small tail of wire hanging from the end of the capillary. The cycle then starts again with the high-voltage electric charge being applied to this tail.

Process where wire is cut right after ball is formed is called stud bumping. Process leaves usually a small tail that is flattend. Stud bumping is used when stacking chips in system in package(SIP) modules.'

The current state-of-the-art machines (as of 2003) can repeat this cycle about 20 times per second. A modern ball bonder is fully automatic and is essentially a self-sufficient industrial robot, complete with a vision system, sensors, and complex servo systems.