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Capillary Profiles Affecting Stitch Bond

The length of the stitch bond is influenced by the capillary tip diameter. The size of the tip diameter is dependent upon the device bond pad pitch dimension. For ultra-fine pitch application, the considerations for good stitch bonds (which means higher pull strength readings) are the following:

Capillary dimensions directly affect the stitch bond formation

 



  • Tip Diameter (T) determines the amount of Stitch Length (SL)

 
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  • Outer radius (OR) must complement face angle (FA) design for given small tip diameter (T) - to provide an adequate thickness and smooth transition of the stitch.


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  • Face Angle (FA) provides a certain level of thickness of the stitch bond with a proper combination of OR transition.This is typically 8° for non-fine pitch and 11° for fine to ultra-fine pitch applications.





 

  • Inner Chamfer (IC) bonds the necessary tail length before detaching it from the stitch bond in preparation for the next FAB formation.

 

Typical Capillary Tip Diameter and Outside Radius Design Combination

Another important consideration in the design of the capillary is the correct combination of outer radius (OR) and the tip diameter (T) with a given face angle (FA). This combination would ensure a smooth transition of the stitch bond as it guarantees that the outer radius (OR) would not nullify whatever face angle design applied, given the tip diameter design. Table 2 shows the typical T and OR combination.


Table 2 

 Tip Diameter (μm / mil)

Outer Radius 'OR’ (μm / mil)

 55 / 2.2

8 / 0.3

 60 / 2.4

8 / 0.3

 65 / 2.6

10 / 0.4

 70 / 2.8

10 / 0.4

 75 / 3.0

12 / 0.5

 80 / 3.1

12 / 0.5

 90 / 3.5

12 / 0.5

 100 / 3.9

12 / 0.5

 110 / 4.3

20 / 0.8

 120 / 4.7

20 / 0.8

 130 / 5.1

30 / 1.2

 140 / 5.5

30 / 1.2

 150 / 5.9

30 / 1.2

 165 / 6.5

38 / 1.5

 180 / 7.1

38 / 1.5

 190 / 7.5

38 / 1.5

 200 / 7.9

51 / 2.0

 225 / 8.9

51 / 2.0

 250 / 9.8

51 / 2.0

 270 / 10.6

51 / 2.0

 300 / 11.8

64 / 2.5

 330 / 13.0

64 / 2.5

 360 / 14.2

75 / 3.0

 
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