Developing a model for the bond heel lifetime prediction of thick aluminium wire bonds

Abstract

Purpose - The purpose of this paper is to establish a law on the durability of thick aluminium wire bonds in low cycle fatigue for different geometries and wire diameters under a purely mechanical load. Design/methodology/approach - Bond wires with different geometries were tested with various loads and a mechanical test bench, and their endurance was determined. The same load situation was modelled with finite element analysis and then compared against the experimental results. Findings - A correlation was found between the plastic strain per cycle and the determined lifespan. Therefore, the lifespan can be calculated by mechanical-plastic simulation for various loop geometries and loading cases. Practical implications - The loop height strongly influences the durability of the wire bond, whereas other parameters, such as the loop angle, have a weaker influence on the bond heel lifetime. Originality/value - The mechanical simulation is able to replace the time-consumin g lifetime experiments

A Fatigue Lifetime Prediction Model for Aluminum Bonding Wires

“…For this purpose, the fit parameters 𝑎 L and b L are determined for all Wöhler lines, plotted as a function of the R-ratios, and then fitted with model functions. For the fit of the model parameters, a quadratic function was chosen for 𝑎 L,Model , see Equation (7), and a linear function was chosen for b L,Model , see Equation (8).…”

“…The wires are processed into bridges by ultrasonic wedge-wedge wire bonding [2][3][4]. The combination of corrosive media and different cyclic mechanical and thermal stresses during operation can lead to fatigue loads on the wire bridges because of the different thermal expansion coefficients of different substrate materials [5][6][7][8]. This can result in heel cracks or bond wire lift-offs, which can lead to a complete failure of the component [1,[9][10][11].…”

“…There are also approaches to characterizing the cyclic mechanical behavior of wire bridges using self-constructed experimental setups, where cyclic loading is applied to the wire bridges by vibration or relative movement of the bond bases. The investigations showed a strong influence of the geometry of the wire bridges on the lifetime of the Metals 2023, 13, 1781 2 of 18 components [6][7][8][21][22][23]. Furthermore, there are approaches to determining the lifetime models of the wire bridges via degeneration due to electromigration by extrapolating the results of accelerated stress tests for high temperatures [24].…”

Reliability Criteria for Thick Bonding Wire

“…However, the power cycling period is long due to the large thermal time-constant of the wires; achieving steady-state conditions during the heating-cooling cycle requires around 3 s [ 1 ]. Therefore, accelerated mechanical fatigue tests were introduced to decrease the required time for PC tests [ 13 , 16 , 17 , 18 ].…”

“…A common conclusion in literature posits that higher loops are more reliable and that they guarantee a longer fatigue life [ 2 , 13 , 15 , 16 , 22 ]. While PC tests have found that thin wires with an aspect ratio (height to length) ≥25% have less flexure and longer fatigue life [ 23 ], this assumption has not been critically examined for thick wires.…”