Wire Bond Contacts Research Articles

Wire bond contact defect identification in battery modules of electric vehicles using pulses and differential voltage analysis

Automotive battery packs for electromobility applications consist of a large number of interconnected battery cells. Different cell-to-busbar joining techniques are utilized, with cylindrical cells frequently being contacted using wire bonding. Failure of individual connections can occur due to strong vibrations during operation and improper stress, making detection by the battery management system a necessity. This study investigates the identification of an electrical wire bond failure in a state-of-the-art electric vehicle module of a Lucid Air with 10 series-connected and 30 parallel-connected cells (10s30p). Four individual cells were characterized extensively in order to generate a simulation model taking into account parameter scatter. The failure case under investigation was simulatively incorporated in one parallel circuit and subsequently replicated in experimental validation measurements at the module level. The results show that this defect can be detected using pulses of C/3 or higher currents at various states of charge. An even more robust detection is achieved using differential voltage analysis of constant current C/20 discharge voltage trajectories. This defect identification method does not require any additional measurement sensors beyond the voltage taps and sensors provided by the manufacturer – with one voltage sensor per parallel circuit – and can therefore be implemented during electric vehicle usage, e.g. at dedicated service checks. A discussion on the applicability and scalability as well as the limitations of the method is provided. All measurement data of the state-of-the-art Lucid battery system is available as open source alongside the article.

Investigation of failure mechanism of aluminum-scandium wire bond contact under active power cycle test

The failure mechanism of aluminum-scandium (Al-Sc) wire bond in comparison with pure Al wire bond under active power cycle (APC) test was investigated. To monitor the degradation of the bond quality, bond shear forces (shear force) were measured over the testing cycles at different level of temperature swing (ΔT). The results show that the Al-Sc wire bond was much more robust than the pure Al wire bond when the ΔT (Tmax) was mild. On the other hand, as the ΔT was increased, the shear force reduction in the Al-Sc wire bond became more and more remarkable. In the cross-sectional analysis of bond contact after the APC tests, a significant crack propagation was observed even for low ΔT conditions for the pure Al wire, and the crack progressed primarily on the wire side of the bond area. As for the Al-Sc wire, while the bond crack was efficiently suppressed for low ΔT conditions, a significant progress of crack was observed at high ΔT conditions, and the crack grew mainly through the Al pad side of the bond area. A detailed analysis at the bond interface after the APC test at high ΔT condition revealed three phenomena at the Al pad side of the bond area: grain coarsening, precipitation of Cu particles, and large void formation. As the material strength is compromised by these effects, the crack grew more easily through the Al pad side of the contact area, resulting in a rapid reduction of shear force at high ΔT. The bond failure mechanism obtained in this study will provide a valuable insight for the future development of high reliability power semiconductor device.

Analysis of the aging mechanism occurring at the bond-wire contact of IGBT power devices during power cycling

This paper focuses on the degradation at the wire bond contact with the metalized pad, and precisely its evolution with the power module aging. In order to induce damage in this particular zone, an accelerated power cycling test is carried out on well-suited devices. The on-state voltage (VCE) is measured during the test as an indicator of the degradation in the wire and metallization. Then, analyses of the interface wire-metallization are done with a numerical microscope and the EBSD (Electron Back-Scattered Diffraction) technique. As a result, an attempt to correlate the evolution of the degradation with the changes in the granular microstructure of the aluminium constituting the wire and metallization is proposed.

Wire-bond contact degradation modeling for remaining useful lifetime prognosis of IGBT power modules

Reliability of power electronic equipment can be enhanced with the ability to predict its health state to avoid damage and permit making necessary maintenance. In this paper, an analytical physics of failure model is built that describes the contact resistance between wire-bonds and pad-metallization in an IGBT semiconductor device. On one hand, this model is based on the theory of the electrical contact resistance and the other hand on the spread of the current from the contact to the aluminum film. When contact degradations occur, the model can relate the crack propagation in the wire-bond interconnection to the collector-emitter voltage (VCE) and may allow identifying the health of the device. If the voltage is measured during actual operation, the length of the contact radius can be estimated and crack propagation rate can be calculated and used to predict the remaining useful life. The approach is tested with experimental accelerated aging tests.

Remaining Useful Lifetime estimation for Electronic Power modules using an analytical degradation model

Power electronic modules undergo electro-thermal stresses due to power losses that lead to several kinds of degradations, and finally to failure. In order to prevent power electronic module failure, one should assess its state of health in real-time operation. For this purpose, Prognostics and Health Management (PHM) approach could be a promising tool for reliability evaluation for an IGBT device. The Insulated Gate Bipolar Transistor is a three-terminal power semiconductor device used as an electronic switch which combines high efficiency and fast switching. In this paper, an analytical model is proposed that describes the metallization to wire-bond contact resistance. This model computes the crack length and then using online measurement the rate of crack propagation is computed and used to predict the future crack lengths with the assumption of linearity in crack propagation. The main failure mechanism of the IGBT device in this paper is the crack propagation in the wire-bond interconnection. The usual aging indicator of such damages is the voltage between the collector and the emitter of current (VCE) that increases with degradation. The analytical model is related to this indicator and it is based on the contact resistance theory and constriction current lines. The proposed model is hence used to build a prognostics model for estimating the remaining useful lifetime (RUL) of IGBT power modules. The prognostics model is illustrated using aging data coming from accelerated power cycling tests with different stress conditions. The first cycling test is under the conditions of stress duration ton = 3sec and junction temperature swing amplitudes ΔTj = 110 ºC and the second cycling test is under ton = 3sec and ΔTj = 90ºC. Results show a prognostics capability.

Analysis of the degradation mechanisms occurring in the topside interconnections of IGBT power devices during power cycling

This paper presents an experimental technique to characterize the damage evolution of the topside interconnections of power semi-conductor devices during power cycling tests. DC power cycling tests are done on Semikron SKIM 63 power modules, a solder-free module with silver sintered chips, ensuring the degradations to appear in the top layers only. The cycled substrates are then extracted from the test bench at different steps of the aging for analysis. Four-probe measurements are implemented on the chips so that the evolution of physical parameters representative of the degradation in the metallization and the bond wire contacts can be obtained. Finally, optical microscopy analysis of cross-sections at the wire bond contact interface is carried out to corroborate the electrical measurements to the crack length growth after specific aging intervals.

Influence of surface contamination on metal/metal bond contact quality

The influence of surface cleanliness of Au/Ni coated multichip materials (MCMs), Ag plated Cu lead frames, and Al bond pads on semiconductor chips on the strength of Au wire bond contacts has been investigated. A clean surface is important for good adhesion in any kind of attachment process. Investigations by means of x-ray photoelectron spectroscopy have been performed on the bond substrates to determine the chemical composition, the nature as well as the thickness of the contamination layer. The influence of contamination on bond contact quality has been examined by pull force measurements, which is an established test method in semiconductor packaging industry for evaluating the quality of wire bonds. The results clearly show that a strong correlation between the degree of contamination of the substrate and pull strength values exists. Furthermore, a contamination thickness limiting value of 4 nm for Au and Ag substrates was determined, indicating good wire bond contact quality. The effect of plasma cleaning on wire bondability of metallic and organic (MCMs) substrates has been examined by pull force measurements. These results confirm the correlation between surface contamination and the strength of wire bond contacts for Au/Ni coated MCMs and Ag plated Cu lead frames. Atomic force microscopy measurements have been performed to determine the roughness of bond surfaces, demonstrating the importance of nanoscale characterization with regard to the bonding behavior of the substrates. Finally, bonding substrates used in integrated circuit packaging are discussed with regard to their Au wire bonding behavior. The Au wire bonding process first results in a cleaning effect of the substrate to be joined and secondly enables the change of bonding energy into frictional heat giving rise to an enhanced interdiffusion at the interface.