Tang Liang

Studies on pressure control of bonding process

This paper discusses different algorithms for pressure control within die bonding process, and presents a new pressure control algorithm with improved performance. For high volume manufacturing with die bonder or flip chip bonder, both precise pressure control and high bonding efficiency are critical to bonding process. Traditional position control method can achieve excellent position accuracy but the impact force during contact is unacceptable. The hybrid force-position control algorithm reduces the impact force by slowing down terminal speed, but how to select the terminal speed is a problem. Lower terminal speed results in smaller impact force but lower efficiency; higher terminal speed results in better efficiency but bigger vibrations which disrupts the stability of bonding pressure. A force sensor can be implemented as feedback to maintain stable bonding pressure; nevertheless its limited responsive bandwidth may decrease system stability. Based on above analysis and dynamic modeling simulation by MSC ADAMS for influences of different factors, a new hybrid position-velocity force control mechanism is presented in this paper. By fine-tuning the motion trajectory with position loop and velocity loop, good efficiency is achieved without force overshoot on contact. By fine designed velocity-force control approach with a disturbance observer, stable bonding pressure is preserved without force sensor. Experimental results show advantages of the proposed algorithm, less than 5% bonding pressure fluctuation is achieved.