High-precision bond head positioning method and apparatus

1. A method for mounting a die at a bonding location, the method comprising the steps of:

picking up a die with a bond head which incorporates a collet for holding the die and for bonding the die at the bonding location;

with a first optical system, viewing and determining a position and orientation of the die relative to the bond head when the die is being held by the collet;

with a second optical system, viewing and determining a position and orientation of the bonding location when the second optical system has its focal plane configured at a first distance from the second optical system;

moving the bond head adjacent to the second optical system, and with the second optical system, viewing and determining a position and orientation of the bond head when the second optical system has its focal plane configured at a second distance from the second optical system which is different from the first distance; and thereafter

adjusting the position and orientation of the die to correct a relative offset between the die and the bonding location prior to depositing the die onto the bonding location.

2. The method as claimed in claim 1 , wherein the bond head comprises a first fiducial mark indicating the position and orientation of the die that is viewable by the first optical system, and a second fiducial mark separate from the first fiducial mark indicating a position and orientation of the bond head that is viewable by the second optical system.

3. The method as claimed in claim 2 , wherein an image captured by the first optical system comprises the die and the first fiducial mark, and images captured by the second optical system comprise the second fiducial mark and the bonding location respectively.

4. The method as claimed in claim 2 , wherein the second fiducial mark is centrally located within the bond head.

5. The method as claimed in claim 4 , wherein the first fiducial mark is located on the collet, and is arranged to be visible to the first optical system when the die is held by the collet.

6. The method as claimed in claim 5 , wherein the second fiducial mark on the bond head is vertically related by an affine transformation to the first fiducial mark on the collet.

7. The method as claimed in claim 2 , wherein the focal plane of the second optical system at the second distance is located substantially at a same height as that of the second fiducial mark.

8. The method as claimed in claim 1 , wherein the bond head further comprises an optical assembly constructed in the bond head for configuring the focal plane of the second optical system at the second distance.

9. The method as claimed in claim 8 , wherein the bond head comprises a hollow space for creating a light path from the second optical system to the optical assembly constructed inside the bond head.

10. The method as claimed in claim 8 , wherein the optical assembly includes a beam splitter and a mirror.

11. The method as claimed in claim 10 , wherein the mirror is further coated with a fiducial mark for indicating a position and orientation of the bond head.

12. The method as claimed in claim 8 , wherein the optical assembly includes a converging lens which converges light rays onto a fiducial mark located on the bond head for indicating a position and orientation of the bond head.

13. The method as claimed in claim 1 , wherein the second optical system further comprises an optical assembly constructed for configuring the focal plane of the second optical system at the second distance.

14. The method as claimed in claim 13 , wherein the optical assembly focuses at least two different wavelengths of light onto the two focal planes at the first and second distances from the second optical system.

15. The method as claimed in claim 14 , wherein the first distance is at a height of a fiducial mark for indicating a position and orientation of the bond head and the second distance is at a height of the bonding location.

16. The method as claimed in claim 14 , wherein the optical assembly includes a converging lens having axial chromatic aberration.

17. The method as claimed in claim 14 , wherein the optical assembly includes a dichroic beam splitter to direct the two different wavelengths of light onto two different light paths, each light path forming an image that is captured by a different imaging sensor.

18. The method as claimed in claim 14 , wherein the optical assembly includes a beam splitter that directs the different wavelengths of light to different dichroic mirrors located at different distances from the beam splitter which respective dichroic mirrors reflect the two different wavelengths of light onto a same imaging sensor.

19. An apparatus for mounting a die at a bonding location, comprising:

a bond head which incorporates a collet for holding the die and for bonding the die at the bonding location;

a first optical system operatives to view and determine a position and orientation of the die relative to the bond head when the die is being held by the collet;

a second optical system operative to view and determine a position and orientation of the bonding location when the second optical system has its focal plane configured at a first distance from the second optical system;

wherein the second optical system is further operative to view and determine a position and orientation of the bond head when the second optical system has its focal plane configured at a second distance from the second optical system which is different from the first distance, when the bond head is moved adjacent to the second optical system;

whereby the position and orientation of the die is adjustable for correcting a relative offset between the die and the bonding location prior to depositing the die onto the bonding location.