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GAISER CAPILLARY INFORMATION

9. INSIDE CHAMFER ANGLE PAGE 1 (2)

The 120 inside chamfer (I.C.) angle is designed for bonding to surfaces with poor bondability. The 90 I.C. angle is designed for bonding to surfaces with good bondability. 

GTC Figure 21

Figure 21. If the ball is not sticking to the pad, one of the following problems may exist: 

bullet Excessive size of free-air ball
bullet Insufficient force, power, heat or dwell time
bullet Residual silicon oxide or contamination on the bonding pad
bullet Prebonded ball size is too small
bullet IC angle is too steep

GTC Figure 22

Figure 22. The 120 I.C. angle produces more downward force than the 90 I.C. angle (see fl and f2 above). This increased downward force affects both the ball bond and the stitch bond. 

 

GTC Figure 23

Figure 23. Ball bonds made with 120 I.C. angles will be wider. This is due to the increased outward deformation of the ball during bonding. The ball shear strengths are typically higher on ball bonds made with capillaries having 120 I.C. angles compared to those with 90 I.C. angles. Tail bonds made with 120 I.C. angles are stronger and tend to produce fewer E.F.O. "opens" or errors. 

(Photo: courtesy ASM Corporation)

GTC Figure 24

Figure 24. If the ball bond formed is larger than desired, a few of the common causes are:  

bullet IC angle too flat
bullet Excessive size of free-air ball
bullet Wire size too large
bullet Excessive force and/or power setting

GTC Figure 25

Figure 25. Ball bonds made with 90 I.C. angles have taller ball bonds and smaller ball bond widths. This is due to the upward deformation equaling the outward deformation of the ball during bonding. As a result, the 90 I.C. angle is sometimes preferred for fine-pitch applications where small ball bonds are desired. The 90 I.C. angle capillary minimizes tailing by cutting through the wire more efficiently. The tail bond is not as strong as the tail bond made with the 120 I.C. angle capillary. The 90 I.C. angle may be used to reduce "peeling up" of the stitch bond or to eliminate "pig tail" bonds. 

(Photo: courtesy ESEC corporation) 

GTC Figure 26

Figure 26. There are many reasons for tailing:

bullet Very good bondability of metallization
bullet IC angle is too shallow
bullet IC size is too large
bullet Excessive wire elongation factor
bullet Wire is too old

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

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