Is Fully Automatic Bond Testing Possible? » Measurement of gross sample position and variations in bond positions

Measurement of gross sample position (Fiducial camera alignment)

Similar to load/unload, referencing of the sample position has been solved for production line equipment but there is the previously mentioned issue where bonds or wires may obscure references used by other equipment that that are no longer available. The advances described in the previous section on illumination generally enable some feature to be used as a reference/fiducial and this together with what is readily available within the industry make this possible in almost every case.

Accurate automatic alignment for variations in bond position

With a state of the art camera, including illumination and image analysis, many variations in bond position can be corrected for automatically. The design of the tool testing the bond is also directly related to alignment. Alignment is the starting point whereby the test method brings the tool into contact with the bond. Optimum alignment cannot be considered without considering the tool and the sample’s geometry. The sample’s geometry is typically fixed so the tool shape must be engineered correctly. Two examples on how tool design can assist alignment are hook foot length (Fig 14) and self-aligning shear tools (Fig 15).

Fig 14. The correct hook foot length works with the maximum possible positional variation as shown by the two extremes marked by red dotted lines
Fig 14. The correct hook foot length works with the maximum possible positional variation as shown by the two extremes marked by red dotted lines
Fig 15. This self-aligning shear tool corrects for the smallest angular difference between tool and sample
Fig 15. This self-aligning shear tool corrects for the smallest angular difference between tool and sample

In some cases the bond cannot be tested without some sample preparation, in which case the design of the prepared sample must be considered. Again in some cases this sample preparation can be done on the bond tester as part of the automation, for example, pushing wires that obscure a fiducial reference of the bond to be tested out of the way.

Fig 16a. Coaxial illumination for fiducial analysis
Fig 16a. Coaxial illumination for fiducial analysis
Fig 16b. Diffused illumination for wire position analysis
Fig 16b. Diffused illumination for wire position analysis

The ability to highlight normal and flat surfaces makes coaxial light often suitable for fiducial marks (Fig 16). Whereas diffused light can assist with the analysis of wires and ball type features (Fig 17).

Fig 17. Wire position can be measured and then hook alignment corrected
Fig 17. Wire position can be measured and then hook alignment corrected

Continue to read:

  1. Introduction
  2. What is Required for Automation?
  3. What is Possible with Modern Automation?
  4. Non-Destruct Testing
  5. Conclusion

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