Copper wire ball bonding has gained considerable attention due to its economic advantage, strong resistance to sweeping and superior electrical performance. In order to have a good first bond, consistent free air-ball formation for copper bonding are even more crucial than they are in the gold wire process.To create a Free Air Ball (FAB), the wire bonder uses an Electronic Flame-Off (EFO) unit, where high voltage is connected. During operation, the EFO gap is breached by a high current, creating a high voltage spark, which melt the tail of the copper wire in a glow discharge to form a spherical ball. Unlike gold wire, copper wire oxidizes readily. Hence, during the formation of the FAB, the copper wire must he enclosed in an inert gas environment in order to prevent oxidisation of the FAB.In this study, an empirical methodology was developed to model a consistent FAB for copper wire diameters ranging from 0.8mil to 2.0mil. Cherry pit bonds were created to study the FAB. Numerous tests were run on an automatic ball bonder in which current and time were varied and the resulting ball size measured. These data points were then used as inputs for the empirical model. This methodology uses the EFO current and time as ' measurable energy inputs and the FAB size as the measurable energy output. It is simple to use and has the advantage of avoiding complex computation of phenomena analysis, which involves the phase change during FAB melting and formation. It is also able to predict copper wire FA6 to provide consistent FAB size. lntroductionWire bonding has been the most popular interconnection method in semiconductor device packaging. Recently, due to the increasing demand for enhancing the reliability of the devices and saving materials costs, attention has been focused on wire bonding using high strength and conductive copper wire.The wire bonding cycle commences with electrical breakdown of the air gap between the wire and wand followed by the discharge which heats and melts the tail of wire. Surface tension causes the melted part to roll up into a ball, in which this ball would then he pressed and formed into first bond by the capillay.In wire bonding, constant ball and wedge dimensions are important for the connection quality. Slight variations in the deformed ball size of the first bond cause yield lossThe key for a reliable ultra fine-pitch copper wire process is the formation of a round, reproducible FAB. To prevent the FAB from oxidising, an inert atmosphere around the tail-EFO wand area during the flame-off phase is created. The shape and size of FAB formation deeply affects the quality of copper wire bonding as it affects the bondability of the first bond as well as the loop height due to its Heat Affected Zone (HAZ).In order to have a consistent FAB formation, precise control of the currentholtage of the EFO has a direct impact on the formation of the FAB (melted ball before actual deformation during the bond process). The EFO generates the spark that melts the end of the copper wire to form the tiny hall.The...
A method has been proposed to model the illumination characteristics of a typical wire bonder vision system. The proposed model can be used to calibrate the illumination of the vision system to ensure the same level of illumination brightness across different machines, given the same lighting level setting. The approach to extract the machine illumination model is semi-empirical and the model provides a closed-form solution.
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