Apparatus and method for dispensing a viscous adhesive

1. A method of dispensing a viscous adhesive for attaching a semiconductor die onto a substrate during operations for dispensing the viscous adhesive onto different locations on the substrate, the method comprising the steps of:

moving a nozzle towards the substrate for dispensing a volume of viscous adhesive from the nozzle onto a first location on the substrate during a respective dispensing operation;

moving the nozzle away from the substrate such that an adhesive tail is formed between the nozzle and the volume of viscous adhesive;

capturing multiple images of the adhesive tail and of the nozzle moving away from the substrate with an imaging device during the dispensing operation as the nozzle is moving away from the substrate;

detecting with the imaging device an instant when the adhesive tail breaks from the volume of viscous adhesive; and thereafter

moving the nozzle towards the substrate and dispensing another volume of the viscous adhesive onto a second location on the substrate during a subsequent dispensing operation.

2. The method of claim 1 , wherein the imaging device is mounted in a fixed relationship to the nozzle such that the imaging device is movable together with the nozzle so as to keep the nozzle within a field of view of the imaging device.

3. The method of claim 1 , further comprising the step of recording a time period between an instant when the nozzle starts to move away from the substrate, and the instant when the adhesive tail breaks.

4. The method of claim 3 , wherein in response to the time period recorded, further comprising the step of changing a parameter used by the nozzle for dispensing the viscous adhesive.

5. The method of claim 4 , wherein the parameter is selected from the group consisting of: a speed at which the nozzle moves away from the substrate, a distance for which the nozzle moves away from the substrate, and a period of time at which the nozzle is at rest after moving away from the substrate.

6. The method of claim 3 , further comprising the steps of:

recording a respective time period for the instance when the adhesive tail breaks when dispensing each volume of viscous adhesive;

entering a plurality of such time periods into a data set;

statistically analyzing the data set; and

changing a parameter used by the nozzle for dispensing the viscous adhesive based on the statistical analysis of the said data set.

7. The method of claim 1 , wherein a processor and a memory are embedded in the imaging device for processing the images captured.

8. The method of claim 7 , wherein the step of capturing multiple images of the adhesive tail is performed at a rate of 500 frames per second or more.

9. The method of claim 1 , further comprising the step of moving the nozzle a horizontal distance over an area of the substrate while dispensing the volume of adhesive so as to dispense the volume of the adhesive to cover the area of the substrate.

10. The method of claim 1 , wherein the step of moving the nozzle away from the 15 substrate comprises moving the nozzle away from the substrate by a predetermined distance to a rest position.

11. The method of claim 10 , further comprising the step of keeping the nozzle at the rest position for a predetermined period of time.

12. The method of claim 9 , further comprising the step of moving the nozzle further away from the substrate after keeping the nozzle at the rest position for the predetermined period of time.