| dc.description.abstract | Taiwan′s semiconductor industry holds a leading position globally, with high-end semiconductors reaching the 5nm technology level. The assembly quality of semiconductors determines their overall quality. Currently, in the gold stud bump process of semiconductors, the procedure involves using gold wire to form gold bumps on semiconductor wafers or individual integrated circuits (ICs). According to the current process requirement for gold stud bump quality, the allowable bump thickness deviation is only ±5 micrometers. However, due to the small size of the gold bumps, it is difficult to measure their height accurately and in real-time. At present, the process conditions are adjusted to maintain yield by controlling the ultrasonic energy and bonding force of the wire bonder and through quality inspection analysis. Nonetheless, this method is not precise enough, representing a common manufacturing bottleneck in the industry.
The experiment in this paper involves attaching a vibration sensor to the spindle of the wire bonding head. The optimal parameters of the wire bonding machine are then fine-tuned. Vibration data corresponding to changes in ultrasonic energy are collected in real-time at a frequency of three times per second, and the mechanical decay rate is calculated every ten seconds. The results are compared with yield rates and photographed. For each experiment, the cross-sectional size and thickness of the gold bump are measured under successful bonding conditions. This experiment will be conducted with five sets of data, which will be analyzed and used to build a database to adjust the optimal production conditions.
Results from the photographs indicate that when only the ultrasonic energy of the optimal parameters is changed, the range of the major and minor axes of the elliptical of the gold stud bump is between 59μm and 83μm, and the bump thickness falls within 13μm to 20μm. During this range, the average vibration intensity measured by the vibration sensor is between 2.285 m/s² and 2.444 m/s², and the average mechanical decay rate during production is between 409 and 610. When the ultrasonic energy is increased to 120mA, the major axis dimension of the gold stud bump′s elliptical cross-sectional exceeds the specification, ranging from 86μm to 91μm. At this time, the average vibration intensity per minute measured by the sensor exceeds 2.483 m/s², and the average mechanical decay rate reaches 611. When the ultrasonic energy is decreased to 50mA, the thickness of the gold stud bump exceeds the specification, falling between 21μm and 23μm. At this time, the average vibration intensity per minute measured by the sensor is less than 2.284 m/s², and the average mechanical decay rate increases to 648.
The results of this paper indicate that changes in the ultrasonic energy of the wire bonder are synchronously reflected in the vibration changes and mechanical decay rate of the spindle, which directly affect the dimensions of the gold stud bumps. The results show that when the average vibration value per minute is within the range of 2.285 m/s² to 2.444 m/s² and the decay rate is below the critical value of 610, the major and minor axis dimensions and the thickness of the gold stud bumps can be controlled within acceptable limits. In other words, by real-time monitoring of the vibration changes in the wire bonder′s spindle, a yield rate of over 99% can be achieved. | en_US |