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GAISER CAPILLARY INFORMATION

11. CHAMFER DIAMETER

GTC Figure 34

Figure 34. The chamfer diameter (B dimension consists of the hole and both sides of the IC. The function of the B dimension is to capture and center the free air ball prior to making the ball bond. Most thermosonic capillaries have IC=0.0004in./10µm or larger.
 

GTC Figure 35

Figure 35. If the free-air ball is formed to one side of the wire as a result of a poor tail bond, the resulting ball bond can be golf club shaped. Reasons for a poor tail bond include:

bullet Inside chamfer too small
bullet Inside chamfer angle too steep
bullet Poor lead metallization
bullet Poor clamping
bullet Contamination

GTC Figure 36

Figure 36. Off-center or golf club shaped ball bonds can also be caused by: 

bullet Inside chamfer is too small or incorrect angle
bullet Wire is too hard
bullet Wire tension/drag is not tight enough
bullet Incorrect vertical distance between the electrode and the end of the wire
bullet Excessive tail length

GTC Figure 37

Figure 37. If the B Dimension is too large, the ball can be "swallowed-up" into the chamfer area. If this happens, the ball may not have enough contact with the bonding pad resulting in weak ball bond or "non-stick." It is also possible for the capillary's tip to touch the pad. Touching the pad can damage the device and cause build-up of die pad metallization on the tip of the capillary.

GTC Figure 38

Figure 38. Scratches on the wire can be caused by:

bullet Damaged Inside Chamfer
bullet Wire from the spool has scratches
bullet Wire clamp surface damaged
bullet Wire clamp not open
bullet Excessive wire drag

GTC Figure 39

Figure 39. This ball bond was made by a worn capillary. The original shape of the inside chamfer is gone, leaving a rough concave surface. This ball bond is strong and will pass bond shear tests, but could fail optical tests. This capillary will eventually start producing bonds with flame-off errors and tailing problems.
 

GTC Figure 40

Figure 40. The capillaries above have the same hole diameter but different dimensions. The smaller B dimension is used when is attempting to form a smaller ball bond. A reduced free-air ball size is recommended when the smaller B dimension is used.
The 90° I. C. angle is often combined with a smaller B dimension to reduce the overall ball bond size. The B volume with a 90° I.C. angle is approximately 45% greater than with a 120° I.C. angle, allowing more of the free air ball to be drawn up into the chamfer diameter. This forms a taller, smaller diameter ball bond than a 120° I.C. capillary with the same B dimension.

Get the BASIC CAPILLARY BONDING and DESIGN document in BASIC CAPILLARY BONDING/ DESIGN format

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Last modified: 2011-11-12