Wire bond with improved shear strength
A wire bonding method and a wire bond formed from the method are provided to improve shear strength of a wire that is connected to a bonding surface. The wire bond includes a bonded wire having a base in contact with the bonding surface, a recessed portion formed substantially at an edge of the bonded wire wherein at least a portion of an underside of the recessed portion is in contact with the bonding surface, and a length of wire extending from the recessed portion.
1. Method for bonding a wire to a bonding surface with a bonding tool, comprising the steps of:
contacting the bonding surface with the wire at a bonding location;
applying bonding energy from the bonding tool to attach the wire to the bonding surface at a bonding point lying along a central longitudinal axis of the bonding tool;
moving the bonding tool away from the bonding location;
contacting the attached wire with the bonding tool at the bonding location at an offset position where the central longitudinal axis of the bonding tool is offset from the bonding point; then
applying bonding force and power to deform the attached wire until an underside of the wire not already in contact with the bonding surface contacts the bonding surface.
2. Method as claimed in claim 1 , further comprising the step of extending the wire from the deformed portion in the attached wire after deforming the attached wire.
3. Method as claimed in claim 2 , wherein the bonding location comprises a first bonding position, and the bonding tool is moved to a second bonding position after deforming the attached wire.
4. Method as claimed in claim 1 , wherein the bonding location comprises a second bonding position of the wire to which the bonding tool is moved after forming a wire bond at a first bonding position.
5. Method as claimed in claim 4 , further comprising the step of severing the wire from the wire bond after forming the wore bond at the second bonding position.
6. Method as claimed in claim 1 , wherein said underside of the wire is bonded to the bonding surface.
7. Method as claimed in claim 1 , wherein the step of moving the bonding tool away from the bonding location comprises the step of moving the bonding tool to a search height.
8. Method as claimed in claim 7 , including the step of moving the bonding tool at a constant search speed from the search height until it contacts the attached wire at said offset position.
9. Method as claimed in claim 1 , including maintaining a position of the attached wire relatively stationary while moving the bonding tool during execution of the method.
10. Method as claimed in claim 1 , further including the step of first forming a molten ball at an end of the bonding wire before attaching the wire comprising the ball to the bonding location.
11. Method as claimed in claim 10 , wherein the step of contacting the bonding tool at said offset position includes the step of first locating the bonding tool over an edge of the ball of wire and then lowering the bonding tool to deform the wire at an edge of the ball of wire.
12. Method as claimed in claim 11 , including the step of forming a stitch bond at said edge of the ball of wire.
13. Method as claimed in claim 1 , wherein the bonding tool comprises a capillary attached to an ultrasonic transducer of a wire bonder machine.
14. A wire bond produced by the method as claimed in claim 1 .