Chip transfer method and apparatus
View Patent ↗In a chip transferring apparatus a wafer ( 44 ) and a lead frame ( 50 ) are positioned. A first chip ( 42 ) is picked up from the wafer ( 44 ) by a transfer head ( 14; 40 a - 40 d ) in a chip pick-up position, while bonding a second chip to the lead frame ( 50 ) by another transfer head in a chip bonding position. The first chip ( 42 ) is then transferred by said one of the transfer heads from the chip pick-up position to the chip bonding position. Next, the first chip ( 42 ) is bonded on the lead frame ( 50 ) by said one of the transfer heads ( 14; 40 a - 40 d ) in the chip bonding position, while another one of the transfer heads picks up a third chip from the wafer ( 44 ) in the chip pick-up position. Each transfer head ( 14; 40 a - 40 d ) comprises a collet ( 66 a - 66 d ) which, through a mechanical coupling, is coupled to another collet for compensating radial forces exerted on the collet relative to said axis of rotation. Vacuum is transferred to the collet from a stationary pressure source by groove sections ( 106 ) in a transfer assembly stator ( 100 ) communicating through a gap ( 104 ) between the rotatable transfer assembly ( 32 ) and the transfer assembly stator ( 100 ) with gas ducts in the transfer head ( 14; 40 a - 40 d ) and the corresponding collet ( 66 a - 66 d ). A chip ( 42 ) is picked up from a wafer ( 44 ) by a needle mechanism ( 224 ).
1. Apparatus for transferring chips from a wafer to a lead frame, comprising:
a wafer-positioning device for positioning a wafer, the wafer comprising chips surfaces thereof extending in a first plane, the first plane having a front face and a back face, the chips surfaces exposed on the front face of the first plane;
a lead frame positioning device for positioning a lead frame, the lead frame comprising a bond surface thereof, the bond surface extending in a second plane which is different from the first plane, the second plane having a front face and a back face, the bond surface exposed on the front face of the second plane, the front face of the second plane facing the front face of the first plane, either parallel (180°) or intersecting at an intersection line to form a dihedral angle of greater than 0° and less than 180°;
a rotatable transfer assembly comprising at least two transfer heads, a first transfer head for picking up a first chip from the wafer in a chip pick-up position, and a second transfer head for bonding a second chip to the lead frame in a chip bonding position; wherein the rotatable transfer assembly is configured to concurrently rotate the first transfer head toward the chip pick-up position of the first transfer head and the second transfer head toward the chip bonding position of the second transfer head; and
a transfer assembly motor for driving the rotatable transfer assembly about an axis of rotation, the axis of rotation extending along a line in a third plane, each point of the third plane being both equidistant to and between the front faces of the first and second planes.
2. Apparatus according to claim 1 , characterized in that the transfer heads are rotatable essentially along a complete circle in a fourth plane, wherein the fourth plane is at right angles to the axis of rotation of the transfer assembly.
3. Apparatus according to claim 2 , characterized in that the transfer heads are spaced regularly along said circle.
4. Apparatus according to claim 1 , characterized in that the number of transfer heads is four.
5. Apparatus according to claim 1 , characterized in that the transfer assembly is rotated in only one direction.
6. Apparatus according to claim 1 , characterized in that each transfer head comprises a collet which, in the chip pick-up position, is movable in a direction essentially at right angles to the first plane, and in the chip bonding position, is movable in a direction essentially at right angles to the second plane.
7. Apparatus according to claim 6 , characterized in that the transfer assembly comprises a counterweight for each collet, each collet being coupled to its corresponding counterweight through a mechanical coupling for compensating radial forces exerted on the collet relative to said axis of rotation.
8. Apparatus according to claim 7 , characterized in that the mechanical coupling is adapted to be driven by a collet drive motor for moving the collet radially relative to said axis of rotation.
9. Apparatus according to claim 8 , characterized in that the transfer assembly motor has the same axis of rotation as the collet drive motor.
10. Apparatus according to claim 7 , characterized in that the counterweight for one collet is another collet of the transfer assembly.
11. Apparatus according to claim 10 , characterized in that said one collet is situated oppositely relative to said other collet with respect to said axis of rotation.
12. Apparatus according to claim 7 , characterized in that the mechanical coupling is a wire.
13. Apparatus according to claim 12 , characterized in that a support of each collet relative to the transfer assembly comprises a pressure spring pretensioning the wire.
14. Apparatus according to claim 13 , characterized in that the pressure spring has a low stiffness.
15. Apparatus according to claim 13 , characterized in that the pretension force is greater than a bonding force to be applied on a chip on a lead frame by the collet of a transfer head.
16. Apparatus according to claim 1 , characterized in that the rotatable transfer assembly is rotatable around a transfer assembly stator, a narrow circumferential gap being provided between the rotatable transfer assembly and the transfer assembly stator, the transfer assembly stator comprising groove sections facing the gap for at least the chip pick-up position and the chip bonding position, respectively, each groove section extending in the circumferential direction and being in communication with a first gas duct, each transfer head of the rotatable transfer assembly comprising at least one collet having a pick-up opening, the pick-up opening being in communication with the gap through a second gas duct.
17. Apparatus according to claim 16 , characterized in that the number of groove sections is equal to the number of transfer heads.
18. Apparatus according to claim 16 , characterized in that each first duct is provided with a controllable valve.
19. Apparatus according to claim 16 , characterized in that the second gas duct at its end facing the gap is provided with a bridging groove extending in the circumferential direction, the bridging groove being adapted to bridge two adjacent groove sections of the transfer assembly stator.
20. Apparatus according to claim 1 , wherein the two front faces intersect at the intersection line, the third plane bisects the dihedral angle, and the axis of rotation is at an offset angle of at least 0° and at most 90° with respect to the intersection line.
21. Apparatus according to claim 20 , characterized in that the dihedral angle is 90°.
22. Apparatus according to claim 20 , characterized in that the offset angle is 0°.