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Low-K Wire Bonding


Advanced Bonding Application


The process for low-k device bonding is very sensitive especially for ultra-fine-pitch bonding. In fact, the most challenging problem with low-k wire bonding is ball bond reliability. A polymer-induced bonding problem occurs when the bond pad is small. If the polymer is soft or heated above its Tg during thermosonic bonding, the small bond pad can partially sink into the polymer during application of bonding force. This lowers the effective bond force after the capillary contacts the pad, and therefore higher ultrasonic energy is required. ‘Cupping’ or sinking can damage low-k diffusion barriers and results in failure.

Problems associated with low-k wire bonding are as follows (typical failure reject criteria):

  •  Non-sticking on bond pad
  •  Metal peeling / de-lamination
  •  Damaged / fractured bond pad
  •  Effects of probe marks
  •  Poor bond shear strength

Although wire bonding has been a well-established technology for many years, the bonding tool design becomes more complex and the process is very sensitive for wire bonding of low-k devices. Stability of ultrasonic energy transmission and lower ultrasonic-generator power are needed to prevent pad damage. From the various evaluations and analysis conducted, the PI capillary design showed the best attributes in terms of efficiency of ultrasonic energy transfer and better bond integrity. Together with the DFX feature, the PI-DFX combination has shown to reduce pad peeling and improved bond integrity with higher percentage of inter-metallic compound in the bond interface.

 90nm low-k, 55µm BPP
 65nm low-k, 48µm BPP

SPT PART NUMBER RECOMMENDATION (pdf)

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