Wire bonding is used to connect electrical contact points of different devices, or different electrical contact points of the same device. When bonding wires made of reactive materials such as copper or aluminum are used for wire bonding, there is a tendency for oxidation of the wire to occur when the heated material reacts with oxygen in the atmosphere. Oxidation of the wire decreases the quality of the subsequent wire bonds that are formed. Therefore, it is necessary to provide a shielding gas comprised of a relatively inert gas such as nitrogen, hydrogen or argon gas to cover and protect the wire during ball formation of a wire ball-bonding process.
The continuing emphasis on better shielding of copper wire during bonding by providing nitrogen and/or hydrogen gas to shield the wire is driving the development of systems that ensure that the gas is captured within the sparking region of the wire, where a molten ball is formed from the wire for copper ball bonding.
An apparatus for containing shielding gas when supplying the inert gas to bonding wire is disclosed in U.S. Pat. No. 6,234,376 entitled “Supplying a Cover Gas for Wire Ball Bonding”. The apparatus includes a gas-containment tube to direct shielding gas to the bonding wire. Transverse in-line orifices are made in the tube to allow the capillary of the bonding tool to enter the gas-containing tube for ball formation, and then to pass through the tube to bond the ball onto a bonding surface.
Another prior art apparatus for containing shield gas is disclosed in U.S. Pat. No. 7,628,307 entitled “Apparatus for Delivering Shielding Gas During Wire Bonding”. Shielding gas is supplied during the bonding of wires to electronic components by way of an apparatus comprising a main body with an elongated slot having a width that extends into the main body from a side of the main body generally in a first direction, and the slot also extends from a top surface to a bottom surface of the main body in a second direction perpendicular to the first direction for the width of the slot. A tip of the capillary is operable to pass through the slot in the second direction while a gas outlet supplies shielding gas into the slot.
A shortcoming of conventional approaches to deliver shielding gas to the capillary is that prior art systems focus on preventing the wire from native oxidation mainly during the sparking of the wire to form a molten ball. There is loss of gas at the openings of the tubes or apparatus such that oxidation protection is not possible outside these openings. Thus, they do not effectively provide gas coverage to prevent oxidation when wire bonding is being performed, or when moving the capillary sideways to various locations unless the capillary is always located inside the gas containment tube during such movement. This limits the versatility of such systems.
It would therefore be desirable to develop an apparatus for supplying shielding gas to a bonding wire that ensures that the wire is protected by shielding gas not only within the sparking range but also along the travelling path of the capillary to the bonding pad, and thus ensuring the quality of the molten ball both before and during bonding of the same is achieved.