Mechanical characterization of gold and copper free air balls in thermosonic wire bond interconnections

Abstract

In current highly integrated microelectronic devices, the thermosonic wire bond interconnections play a fundamental part in terms of reliability considerations. To avoid chip damage risks, especially if bonding is applied to state-of-the-art ICs containing mechanically sensitive low-K dielectric materials, knowledge of the local deformation behavior of the free air ball (FAB) is essential. The significance of damage risks increases even more if gold wires are to be replaced by copper wires. In this study, the hardening behavior of FABs from two typical gold bonding wires and one copper wire was characterized using a modified micro compression test. In this test, the FAB has been loaded in a direction perpendicular to the wire axis. We calculated the stress/strain behavior via parameter identification using finite element simulations from the experimental force/displacement curves. The mechanical properties of the FABs were compared to those of the unaffected wire. To me chanically characterize the FAB in a loading situation rather comparable to a real bond process, a capillary compression test setup was additionally developed. Both approaches allow an extended deformation characterization of bonding wires considering also the FAB properties. Therefore, they support material selection for wire material development and wire bonding application

Comprehensive modeling and analysis of copper wire bonding process

“…Lorenz [8] got the stress-strain curves by micro compression test. In the present study, we use Lorenz's curve as the initial property of Cu FAB, and then adjust it to match the simulation and experiment.…”

“…Measuring mechanical properties of the FAB is quite challenging due to FAB's small size [8]. (b) The material deformation behavior under the ultrasound is still not clear.…”

Electron backscatter diffraction microstructure investigations of electronic materials down to the nanoscale

“…Here, the system reliability is strongly influenced by loop stability which is strongly affected by elastic properties of the bonding wire material itself as well as by the geometry, length and hardening behavior of heat affected zone just above the ball where grains are recrystallized during the flame-off process [7][8]. Thus a consequent determination of elastic deformation properties of the different bonding wire materials and their relationship to the respective grain microstructure is of utmost importance for material selection as well as for optimization of design and manufacturing processes.…”

Simulations of damage and fracture in ULK under pad structures during Cu wirebond process

“…These models/simulations must provide insights into (a) deformation and stress in free air ball, pad, and die (b) the risk of ULK fracture during impact stage and ultrasonic vibration 978-1-4799-5267-0/14/$31.00 ©2014 IEEE steps. However, few such modeling attempts appear to exist in the current literature [5,6].…”