Ultrasonic stresses in thermosonic ball bonding

Abstract

The risk of chip damage due to ultrasonic stresses in ball bonding needs to be managed while assuring a high bond strength. Chips with low-k dielectrics are less robust than those with SiO2, and if novel Cu or Pd coated Cu bonding wire is used, larger stresses are common during bonding. A finite element model can predict stresses at all locations under the pad including those due to the dynamics of the bonding tool. An experimental verification of these tool dynamics has not been done and is suggested using integrated piezo-resistive stress microsensors on a custom made testchip. The suitability of such a stress sensor design is discussed.