Copper ball bond features and structure
An integrated circuit wire bond connection is provided having an aluminum bond pad ( 51 ) that is directly bonded to a copper ball ( 52 ) to form an aluminum splash structure ( 53 ) and associated crevice opening ( 55 ) at a peripheral bond edge of the copper ball ( 54 ), where the aluminum splash structure ( 53 ) is characterized by a plurality of geometric properties indicative of a reliable copper ball bond, such as lateral splash size, splash shape, relative position of splash-ball crevice to the aluminum pad, crevice width, crevice length, crevice angle, and/or crevice-pad splash index.
1. An integrated circuit wire bond connection comprising:
a copper bond wire comprising a copper ball and an aluminum bond pad that is directly bonded to the copper ball to form an aluminum splash structure and associated crevice opening between the aluminum splash structure and copper ball at a peripheral bond edge of the copper ball, where the aluminum splash structure is characterized by a first plurality of geometric features indicative of a reliable copper ball bond.
2. The integrated circuit wire bond connection of claim 1 , where the first plurality of geometric features for the aluminum splash structure comprises:
a lateral splash size measure of the lateral extent of the aluminum splash structure which extends at least substantially to, but not substantially past, an outer perimeter of the copper ball;
a splash height measure of the vertical distance from a top surface of the aluminum bond pad to a top surface of the aluminum splash structure that is less than half a ball bond height measure for the copper ball and more than half an original pad thickness measure for the aluminum bond pad; and
a gap height measure of the vertical distance from a lowest point of the crevice opening to the top surface of the aluminum splash structure that is less than the splash height measure.
3. The integrated circuit wire bond connection of claim 1 , where the first plurality of geometric features for the aluminum splash structure comprises an elevated splash pad measure of the lateral extent of a base portion of the aluminum splash structure that is less than or equal to twice the lateral splash size measure.
4. The integrated circuit wire bond connection of claim 1 , where the crevice opening between the aluminum splash structure and copper ball is characterized by a second plurality of geometric features indicative of a reliable copper ball bond.
5. The integrated circuit wire bond connection of claim 4 , where the second plurality of geometric features for the crevice opening comprises:
a crevice initiation plane intersecting the lowest point of the crevice opening and positioned above a top surface of the aluminum bond pad; and
a crevice mouth width measure and a crevice length measure, where a ratio of the crevice mouth width measure to the crevice length measure is approximately 20 percent.
6. The integrated circuit wire bond connection of claim 5 , where the crevice mouth width is measured along a first tangent line from a first tangent intersection point on the aluminum splash structure to a second tangent intersection point on the copper ball, and where the crevice length measure is measured along a line from the lowest point of the crevice opening to a midpoint on the first tangent line.
7. The integrated circuit wire bond connection of claim 5 , where the crevice mouth width is measured along a first tangent line (1) that extends from a first tangent intersection point on the aluminum splash structure to a second intersection point on the copper ball, and (2) that is perpendicular to a second tangent line extending from the lowest point of the crevice opening to a second tangent intersection point on the aluminum splash structure; and where the crevice length measure is measured along a line from the lowest point of the crevice opening to the first tangent line.
8. The integrated circuit wire bond connection of claim 1 , where the aluminum splash structure is characterized by a crevice-pad splash index angle that is within a range of 20-75°.
9. The integrated circuit wire bond connection of claim 8 , where the crevice-pad splash index angle is included between (1) a first line defining a top surface of the aluminum bond pad and intersecting with a vertical line intersecting the lowest point of the crevice opening at a vertical crevice extension point N, and (2) a second splash extension line from the vertical crevice extension point N to a splash extension point M that is at a perpendicular intersection between horizontal and vertical tangent planes intersecting the aluminum splash structure.
10. The integrated circuit wire bond connection of claim 1 , where the first plurality of geometric features for the aluminum splash structure comprises:
one or more geometric features for inner and outer segments of the aluminum splash structure in a first cross section that is parallel to movement of a wire bond transducer used to bond the copper ball bond to the aluminum bond pad; and
one or more geometric features for lateral segments of the aluminum splash structure in a second cross section that is transverse to movement of the wire bond transducer used to bond the copper ball bond to the aluminum bond pad.
11. The integrated circuit wire bond connection of claim 1 , where the copper ball is attached to the aluminum bond pad by applying ultrasonic vibration energy to the copper ball in a first direction.
12. The integrated circuit wire bond connection of claim 11 , where the first plurality of geometric features indicative of a reliable copper ball bond comprises a first plurality of larger geometric features evaluated in a cross section that is parallel to the first direction and a second plurality of smaller geometric features evaluated in a cross section that is perpendicular to the first direction.
13. The integrated circuit wire bond connection of claim 1 , where each of the first plurality of geometric features is controlled to be within a predetermined range.
14. The integrated circuit wire bond connection of claim 5 , where the crevice mouth width is measured along a first line from a topmost point on the aluminum splash structure to an intersection point on the copper ball, where the first line is perpendicular to a second line extending from the lowest point of the crevice opening to the topmost point on the aluminum splash structure, and where the crevice length measure is measured along a line from the lowest point of the crevice opening to a midpoint on the first line.
15. The integrated circuit wire bond connection of claim 14 , where the aluminum splash structure is characterized by a crevice-pad splash index angle within a predetermined range that is included between (1) an aluminum bond pad surface line parallel to a top surface of the aluminum bond pad and extending from an aluminum pad elevation point P to intersect with a vertical line intersecting the lowest point of the crevice opening at a vertical crevice extension point N, and (2) a splash extension line from the vertical crevice extension point N to a splash extension point T that is at an intersection between (a) a horizontal extending through the topmost point on the aluminum splash structure, and (b) and a tangent line extending from the aluminum pad elevation point P to a tangent intersection point on the aluminum splash structure.
16. A method of forming a copper ball bond, comprising:
forming a bonding wire comprising a copper ball;
positioning the copper ball at a bonding site at an aluminum bond pad; and
bonding the copper ball to an aluminum bond pad with a predetermined combination of heat, pressure and ultrasonic vibration energy applied in a first direction to form an intermetallic connection layer between the copper ball and the aluminum bond pad and an aluminum splash structure and associated crevice opening between the aluminum splash structure and the copper ball, where the aluminum splash structure is characterized by a first plurality of geometric features indicative of a reliable copper ball bond, comprising a first plurality of larger geometric features evaluated in a cross section that is parallel to the first direction and a second plurality of smaller geometric features evaluated in a cross section that is transverse to the first direction.
17. The method of claim 16 , where bonding the copper ball to the aluminum bond pad with the predetermined combination of heat, pressure and ultrasonic vibration energy comprises:
preheating the bonding wire an copper ball to a preheat temperature of approximately is 170° C.; and
heating the copper ball and aluminum bond pad to a bonding temperature of approximately 200° C. when bonding the copper ball to the aluminum bond pad while supplying bonding power current of approximately 88 to 93 mA and applying a bonding force of approximately 40-45 g during a bonding time of approximately 20 msec.
18. The method of claim 16 , where the first plurality of geometric features for the aluminum splash structure comprises:
a lateral splash size measure of the aluminum splash structure which extends at least substantially to, but not substantially past, an outer perimeter of the copper ball;
a vertical splash height measure from a top surface of the aluminum bond pad to a top surface of the aluminum splash structure that is less than half a ball bond height measure for the copper ball and more than half an original pad thickness measure for the aluminum bond pad;
a vertical gap height measure from a lowest point of the crevice opening to the top surface of the aluminum splash structure that is less than the vertical splash height measure; and
a crevice-pad splash index angle that is within a range of 20-75°.
19. The method of claim 18 , where the crevice opening between the aluminum splash structure and copper ball is characterized by a second plurality of geometric features indicative of a reliable copper ball bond, comprising:
a crevice initiation plane intersecting the lowest point of the crevice opening and positioned above the top surface of the aluminum bond pad; and
a crevice mouth width measure and a crevice length measure, where a ratio of the crevice mouth width measure to the crevice length measure is greater than or equal to 0.1.
20. The method of claim 19 , where the crevice mouth width is measured along a first tangent line (1) that extends from a first tangent intersection point on the aluminum splash structure to a second intersection point on the copper ball, and (2) that is perpendicular to a second tangent line extending from the lowest point of the crevice opening to a second tangent intersection point on the aluminum splash structure; and where the crevice length measure is measured along a line from the lowest point of the crevice opening to a midpoint on the first tangent line.