In industrial practice, frequencies from 40 kHz up to 160 kHz are currently employed for wirebondingwhile for experimental purposes, lower and higher frequencies from around 25 kHz up to 300 kHzare discussed. Typically, heavy aluminium wire or ribbon is preferably bonded at lower frequenciesbetween 40 and 80 kHz, while thin aluminium or gold wires are wedge- or ball-bonded at frequenciesbetween 100 and 140 kHz.We present a discussion of the pros and cons of different ultrasonic frequencies by looking at themechanics during the bonding process. Higher frequencies allow shorter bonding times and permitbonding on more sensitive surfaces, but suffer from a narrower parameter window. This is mainly due tothe smaller vibration amplitudes at the tool tip which can be employed for higher frequencies. The majorbenefit for many applications is that higher bond quality is possible even at lower wire deformation whichadditionally creates a healthier bond heel. Lower frequencies, on the other hand, seem to haveadvantages for rougher surfaces where some planarizing and smoothing is required before bonding canbegin to take place, while running a higher risk of damaging the bond after forming it.Resonance effects can seriously damage bond formation, and ways are discussed on how to dealwith this problem.
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