Patent Application
20110101073
The invention relates to wire bonders, and in particular to wire-feeding systems for wire bonders.
Automatic wire bonders are used during semiconductor assembly and packaging for making electrical wire connections between electrical contact pads on a die and a substrate, or between electrical contact pads on different dice. Wire is fed from a wire spool containing bonding wire, typically gold or copper wire, to a bonding tool such as a capillary for performing wire bonding at the bonding tool.
Along the feeding route of the wire between the wire spool and the capillary, the wire passes through various devices, which may include a pneumatic device and a wire clamp for controlling feeding of the wire during wire bonding.
A shortcoming of such a conventional wire bonder design is that wire threading has to be conducted manually when the bonding wire is being set up for wire bonding. Due to the small dimensions of the bonding wire and devices it has to be threaded through, a skilled technician is required to perform manual wire threading, and even then, the process itself is a time-consuming one.
Moreover, broken wire may occur during wire bonding due to various reasons, such as short tail arising from premature termination of a tail bond, missing ball leading to incorrect formation of a ball bond, and other reasons. Each time there is a broken wire, the wire bonder needs to be stopped and the bonding wire has to be rethreaded manually again, thereby incurring unnecessarily long downtimes and incurring penalties in terms of productivity.
It is thus an object of the invention to seek to provide a system and method for automatically threading the wire of a wire bonder, such as in cases of broken wire, in order to help to free valuable skilled labour for other tasks, and to reduce machine downtime.
According to a first aspect of the invention, there is provided a method for feeding wire to a bonding tool of a wire bonder, comprising the steps of: locating the wire in a pneumatic device; urging the wire with the pneumatic device to feed through a clamping point of a wire clamp located adjacent to the pneumatic device and a hole of a wire guider located adjacent to the wire clamp between the wire clamp and the bonding tool; and urging the wire with the pneumatic device to feed through the bonding tool.
According to a second aspect of the invention, there is provided a method for feeding wire to a bonding tool of a wire bonder when a broken wire is detected during wire bonding and the wire is separated from the bonding tool, comprising the steps of: clamping the wire with a wire clamp while the wire is located in a pneumatic device; feeding a length of wire from a wire source towards the pneumatic device; opening the wire clamp to unclamp the wire; urging the wire with the pneumatic device to feed through a hole of a wire guider which is located adjacent to the bonding tool between the pneumatic device and the bonding tool; and urging the wire with the pneumatic device to feed through the bonding tool.
According to a third aspect of the invention, there is provided an apparatus for feeding wire to a bonding tool of a wire bonder, comprising: a pneumatic device that is operative to urge the wire to feed through an outlet of the pneumatic device towards the bonding tool; a wire clamp located adjacent to the outlet of the pneumatic device; and a wire guider with a hole which is located adjacent to the wire clamp between the wire clamp and the bonding tool for threading the wire through the hole before being fed to the bonding tool.
It would be convenient hereinafter to describe the invention in greater detail by reference to the accompanying drawings which illustrate one embodiment of the invention. The particularity of the drawings and the related description is not to be understood as superseding the generality of the broad identification of the invention as defined by the claims.
Examples of preferred embodiments of a system and method in accordance with the invention will now be described with reference to the accompanying drawings, in which:
Immediately below the pneumatic device 14 and located adjacent to the outlet of the pneumatic device 14 is a lower wire clamp 16 located along the wire feeding route. The lower wire clamp 16 is operable to clamp onto the bonding wire 10 at a clamping point to restrain its movement during wire bonding. When the pneumatic device 14 is activated, a vacuum suction force is applied on the bonding wire 10 to urge and feed it through the clamping point of the lower wire clamp 16 in a direction towards the bonding tool.
The lower wire clamp 16 should be as close to the pneumatic device 14 as possible. The larger the distance, the greater the risk of bonding wire 10 being fed outside the confines of the lower wire clamp 16, which may then lead to wire bend and failed wire threading. Thus, where the lower wire clamp 16 is rotatable between an upper position and a lower position, then at the upper position of the lower wire clamp 16 when it is swung upwards, the distance between the outlet of the pneumatic device 14 and the lower wire clamp 16 should preferably be between 0.5 mm and 10 mm.
The wire guider 18 is located adjacent to the lower wire clamp 16 between the lower wire clamp 16 and the bonding tool. The wire guider 18 may be mounted onto a base of the lower wire clamp 16 and has a small hole for threading and guiding the bonding wire 10 through the hole along the wire feeding route to the bonding tool. The bonding wire 10 is then fed to the bonding tool, such as a capillary 20 located at one end of a transducer horn 22. The transducer horn 22 may be part of an ultrasonic transducer. Bonding wire 10 protruding from a lower tip of the capillary 20 is used to perform wire bonding at the tip of the capillary 20.
Furthermore, with the assistance of an upper wire clamp 12, bonding wire 10 may also be fed towards the capillary 20 by swinging up the transducer horn 22 together with the capillary 20 towards the wire guider 18 while restraining movement of the bonding wire 10 by clamping the bonding wire 10 with the upper wire clamp 12. This action forces bonding wire 10 to be fed to the capillary 20 and is an alternative to providing a pneumatic downwards force at the pneumatic device 14. Another advantage of this feeding action of swinging up the transducer horn 22 and capillary 20 is that, by ensuring adequate feeding of bonding wire to the tip of the capillary 20, it helps to eliminate or reduce the risk of short tail or missing ball occurring.
For feeding of bonding wire 10 prior to commencing wire bonding, bonding wire 10 is first manually inserted into the pneumatic device 14 by an operator to locate the bonding wire 10 in the pneumatic device 14. Thereafter, the pneumatic device 14 is activated to apply a downwards vacuum suction force onto the bonding wire 10. The downwards vacuum suction force will automatically push the bonding wire 10 through the lower wire clamp 16, wire guider 18 and capillary 20 until the bonding wire 10 protrudes through the tip of the capillary 20. The wire bonder is now ready to perform wire bonding.
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Meanwhile, bond stick detection is continuously performed at short intervals to determine the exact point in time when the bonding wire 10 contacts the conductive surface 26. Bond stick detection is a typical feature in bonding machines and refers to a process during wire bonding wherein the bonding apparatus checks whether an electrical current is passing through the bonding wire 10. If so, this indicates a closed electrical circuit formed by the bonding wire 10. When a closed electrical circuit is detected indicating contact between the bonding wire 10 and the conductive surface 26, further feeding of bonding wire 10 to the bonding tool 20 is stopped so that the correct tail length is automatically obtained.
It should be appreciated that the automatic wire feeding systems according to the preferred embodiments of the invention reduce manual intervention for threading bonding wire in a wire bonding system. This frees up skilled labour to perform other tasks and also improves productivity by shortening the time required for threading bonding wire. Moreover, with the assistance of a upper wire clamp 12 above the pneumatic device 14, a wire bonding process can be speeded up by reducing delay for making a second bond through more reliable feeding of bonding wire 10 to the capillary 20.
The invention described herein is susceptible to variations, modifications and/or additions other than those specifically described and it is to be understood that the invention includes all such variations, modifications and/or additions which fall within the spirit and scope of the above description.
