TA.TEC Consulting
Can the Ultrasonic Current Signature Reveal Bond Quality?
What the generator current during bond formation can reveal about attached area and thermal-cycling reliability.
The study investigated whether the ultrasonic-generator current during bond formation can provide information about bond quality.
Changes at the bond interface influence the mechanical impedance of the ultrasonic system and therefore the generator current. The study used 375 µm 5N aluminum wire on an F&K Delvotec wedge bonder at approximately 58 kHz.
The measured current signatures were compared with attached area and thermal-cycling lifetime. Clear differences were observed between weaker and more robust parameter designs.
Under the investigated conditions, the ultrasonic current signature was consistent with independent measurements of attached area and thermal-cycling lifetime.
The stronger design showed a more uniform current signal, larger attached area, and higher average lifetime.
Signal analysis can therefore support fast, non-destructive evaluation of how bonding parameters affect bond quality.
The results apply to the investigated bonding process using 375 µm 5N aluminum wire, the F&K Delvotec wedge bonder, and the tested parameter designs.
The study shows consistency between current signature, attached area, and thermal-cycling lifetime, but does not establish a universal quality threshold for other wire materials, wire diameters, bonders, or process conditions.
Research Source
E. Arjmand, P.A. Agyakwa, C.M. Johnson
Reliability of thick Al wire: A study of the effects of wire bonding parameters on thermal cycling degradation rate using non-destructive methods
Microelectronics Reliability, Volume 54 (2014), 2006–2012
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