Optically clear adhesive (OCA) has been widely used in flexible devices, where wavy stripes that cause troublesome long-term reliability problems often occur. The complex mechanical behavior of OCA should be studied, as it is related to the aforementioned problems. Therefore, it is necessary to establish reasonable mechanical constitutive models for deformation and stress control. In this work, hyperelastic and viscoelastic mechanical tests were carried out systematically and relative constitutive models of OCA material were established. We found that temperature has a great influence on OCA’s mechanical properties. The stress and modulus both decreased rapidly as the temperature increased. In the static viscoelasticity test, the initial stress at 85 °C was only 12.6 kPa, 57.4% lower than the initial stress at 30 °C. However, in the dynamic test, the storage modulus monotonically decreased from 1666.3 MPa to 0.6628 MPa as the temperature rose, and the decline rate reached the maximum near the glass transition temperature (T_g = 0 °C). The test data and constitutive models can be used as design references in the manufacturing process, as well as for product reliability evaluation.

Ag paste has been recognized as a promising substitute for Sn/Pb solder in SiC or GaN power electronic devices, owing to its ability to withstand high temperatures and facilitate low-temperature packing. The reliability of these high-power circuits is greatly influenced by the mechanical properties of sintered Ag paste. However, there exist substantial voids inside the sintered silver layer after sintering, and the conventional macroscopic constitutive models have certain limitation to describe the shear stress–strain relationship of sintered silver materials. To analyze the void evolution and microstructure of sintered silver, Ag composite pastes composed of micron flake silver and nano-silver particles were prepared. The mechanical behaviors were studied at different temperatures (0–125 °C) and strain rates (1 × 10⁻⁴–1 × 10⁻²) for Ag composite pastes. The crystal plastic finite element method (CPFEM) was developed to describe the microstructure evolution and shear behaviors of sintered silver at varied strain rates and ambient temperatures. The model parameters were obtained by fitting experimental shear test data to a representative volume element (RVE) model built on representative volume elements, also known as Voronoi tessellations. The numerical predictions were compared with the experimental data, which showed that the introduced crystal plasticity constitutive model can describe the shear constitutive behavior of a sintered silver specimen with reasonable accuracy.

To enhance the electrical performance and reliability of SiC power modules, the study explores Cu-clip as a promising alternative to traditional Al-wire interconnections. SiC power modules, particularly in parallel configurations, encounter challenges in optimizing dynamic current-sharing performance, which limits their maximum current capacity and reliability during switching events. This study proposes an innovative layout design for SiC MOSFET modules, utilizing a coupled parasitic inductance network model to capture better the impact of mutual inductances on dynamic current imbalance. The model derives an equation for equivalent source inductances, accounting for both self-inductance and mutual inductance, providing a foundation for optimizing the layout to minimize dynamic current imbalance. Based on this model, a new Cu-clip structure is designed along with a mathematical analysis aimed at reducing disparities in equivalent source inductances, thereby enhancing dynamic current balancing. The distance between the dies is also increased to mitigate thermal coupling effects. Double pulse tests and simulations were performed to validate the dynamic current balancing performance of the fabricated power module. The results show a 40% reduction in dynamic current imbalance for the optimized layout (Layout B) compared to the baseline configuration (Layout A). This work presents a comprehensive solution to improve the dynamic current performance of paralleled SiC MOSFET power modules, offering significant contributions to the design of more efficient and reliable power electronics.

There is an increasing demand for the use of automotive sensors where complex working environments may easily lead to failure. Wire pull and shear test models based on finite-element analysis are established to evaluate their reliability by investigating the failure mode and mechanism of gold wire bonding. The effect of shear force position and pull force position on failure is also analyzed. The bonding failure was verified by experiments, which is consistent with the simulation result. The results show that: (1) The three-dimensional quantitative modeling reveals the process of bonding delamination and stress concentration. (2) The bonding–slip method (BSM) is adopted in the gold ball detaching process. The concept of three states, including deformation accumulation, cracking, and disengagement, was put forward to reveal the interface stress evolution trend according to the shear testing results. The results indicate that in the interface, the stress in the deformation accumulation state decreases from the tensile side (or compression side) to the center, and the stress in the cracking and disengagement states reduces gradually from the tensile side to the edge. When the interface is completely separated, the failed shear force concentrates on 42 g. The concept and theory proposed in this work can effectively reveal the failure mechanism of bonding interface and help to establish a new failure criterion.

In the interconnects of microelectronic package with high current density and high-frequency fluctuation, electromigration (EM) events cause the cavities nucleation at the metal lines cathode and hillock pile-up at anode, which further lead to short circuit/open circuit and influence the overall device reliability substantially. In this work, mechanical modeling of EM-induced cavity failure was investigated and a modeling theory of efficient EM cavity morphology evolution based on physics was comprehensively introduced. According to mass diffusion theory, a dynamic model of elliptical cavity shape evolution with velocity and shape parameters was established. Meanwhile, kinetic equations of shape evolution expansion connected to cavity velocity and shape were proposed to explain the cavity expansion and cavity collapse processes, respectively. Based on the surface morphology analysis, it is obvious that cavity evolution form is determined by the competition between surface tension and electron wind. It is revealed that both them encourage cavity stretching in the direction of electric field intensity while compressing in the opposite. In addition, the mismatch of matter concentration between the left and right ends of the cavity will drive the cavity to migrate against the electric field intensity.