Aleksandra Fortier

Comparative Study of Metal Films and Their Affinity for Metal Whisker Growth

The problem of tin (Sn) whiskers has been a significant reliability issue in electronics for the past several decades. Despite the large amount of research conducted on this issue, the growth of whiskers remains a challenge for the research community. A comparative study of different metal whiskers could provide a deeper insight toward the development of more permanent mitigation strategies for Sn whisker growth. In this paper, the surface and microstructural evolution of various film/substrate combinations of 10-μm thick zinc (Zn) and Sn metal films and their affinity for whisker growth were observed under two environmental conditions-ambient temperature and elevated temperature of 55°C and 85% humidity. The films were analyzed using a scanning electron microscope, focused ion beam, and electron dispersive spectroscope. In addition, several decades-aged samples with Zn, Sn, and cadmium films with a high density population of whiskers were observed for comparison.

Investigation of Stent Implant Mechanics Using Linear Analytical and Computational Approach

Stent implants are essential in restoring normal blood flow in atherosclerotic arteries. Recent studies have shown high failure rates of stent implants in superficial femoral artery (SFA) as a result of dynamic loading environment imposed on the stent implants by the diseased arterial wall and turbulent blood flow. There are variety of stent designs and materials currently on the market however, there is no clear understanding if specific stent design is suitable with the material that is manufactured from and if this combination can sustain the life-cycle that the stent implants need to undergo once inside the artery. Lack of studies have been presented that relate stent mechanical properties with stent geometry and material used. This study presents linear theoretical and computational modeling approach that determines stent mechanical properties with effective stiffness of the deployed stent. Effective stiffness of the stent has been accurately derived based on stent structure design and loading in axial and radial directions. A rhombus stent structure was selected for this study due to its more common use and produced by main stream manufacturers. The derived theoretical model was validated using numerical finite element modeling approach. Results from this study can lead to preliminary insight towards understanding of stent deformation based on stent geometry, material properties and artery wall pressure; and how to carefully match stent’s geometry with suitable material for long life cycle, increased strength, and reliable performance of stent implants.

Fundamental FEM Modeling Approach of Residual Stress Propagation in Sn-Based Electroplated Films Prone to Sn Whiskers Growth

The evolution of residual stress gradients in three different cases of electrodeposited Sn-based films on brass substrate has been evaluated using thermomechanical finite element model (FEM), with temperature as the only loading condition. The FEM model for each of the three cases consists of a brass substrate with the following films: 1) pure Sn film; 2) pure Sn film with the Ni-underlayer; and 3) composite Ni/Sn film. The simulations consider the stress behavior under temperature loading, in the electrodeposited Sn-based films with and without the Ni-underlayer(s). A simple analytical model has been developed to estimate the resulting stress gradient (considered as one of the main causes for Sn whiskers growth) in each film. The modeled stress in the films is shown to be in good agreement with the previously published experimental measurements [Dimitrovska et al., Journal of Electronic Materials 38, 2516 (2009)].

Internal Microstructure Investigation of Tin Whisker Growth Using FIB Technology

The problem of tin (Sn) whiskers has been a significant reliability issue in electronics for the past several decades. Despite the large amount of research conducted on this issue, a solution for mitigating the growth of whiskers remains a challenge for the research community. Whiskers have unpredictable growth and morphology, and a study of a whisker’s internal structure may provide further insights into the reason behind their complex growth. This study reports on the internal microstructure and morphology of complex-shaped Sn whiskers grown from an electroplated bright Sn layer on brass substrates exposed to ambient and 95% humid environment. The variables analyzed include surface and microstructure conditions of the film, and morphology and internal microstructure of the Sn whiskers using scanning electron microscopy with focused ion beam technology. Experimental results demonstrated that the whiskers with more complex morphology grow primarily from surfaces exposed to a controlled environment, and some of them have traits of polycrystalline growth rather than only single crystalline, as usually known.

A perspective of the IPC report on lead-free electronics in military/aerospace applications

Abstract Significant progress towards lead-free technology implementation has been made in the last decade. However, majority of the successful transition has been done within consumer electronics industry while high reliability military/aerospace products are yet to fully transition. This study discusses viewpoint on the recent IPC report published on lead-free electronics in military and aerospace applications. Additionally, reliability considerations are discussed, and guidelines along with standards for robust transition and implementation towards lead-free technology is presented. A “preventive” transition approach based upon more accurate models of failure mechanisms and life prediction than are currently available will be required in order to assess successful implementation within military/aerospace products and for high reliability to be achieved.