In 3D packaging memory devices, solder joints are critical links between the chip and the printed circuit board (PCB). Under severe working conditions, cracks inevitably occur due to thermal shock. If cracks grow in the solder joint, the chip will be disconnected with the PCB, causing its function failure. In this paper, the reliability of solder joints under thermal shock are evaluated for 3D packaging memory devices by means of the SEM and finite element analysis. As microscopically studied by the SEM, it is found out that the main failure mechanism of solder joints in such test is the thermal fatigue failure of solder joints. Finite element analysis shows that cracks are caused by the accumulation of plastic work and creep strain. The initiation and growth of cracks are mainly influenced by the inelastic strain accumulation. The trends of cracks are influenced by the difference between the coefficient of thermal expansion (CTE) of epoxy resin and that of the chip.

Bionic structures are widely used in scientific research. Through the observation and study of natural biological structure, it is found that spider web structure is composed of many radial silk lines protruding from the center and spiral silk lines surrounding the center. It has high stability and high sensitivity, and is especially suitable for the production of sensors. In this study, a flexible graphene sensor based on a spider web bionic structure is reported. Graphene, with its excellent mechanical properties and high electrical conductivity, is an ideal material for making sensors. In this paper, laser-induced graphene (LIG) is used as a sensing material to make a spider web structure, which is encapsulated onto a polydimethylsiloxane (PDMS) substrate to make a spider web structured graphene flexible strain sensor. The study found that the stress generated by the sensor of the spider web structure in the process of stretching and torsion can be evenly distributed in the spider web structure, which has excellent resonance ability, and the overall structure shows good structural robustness. In the experimental test, it is shown that the flexible stress sensor with spider web structure achieves high sensitivity (GF is 36.8), wide working range (0–35%), low hysteresis (260 ms), high repeatability and stability, and has long-term durability. In addition, the manufacturing process of the whole sensor is simple and convenient, and the manufactured sensor is economical and durable. It shows excellent stability in finger flexion and extension, fist clenching, and arm flexion and extension applications. This shows that the sensor can be widely used in wearable sensing devices and the detection of human biological signals. Finally, it has certain development potential in the practical application of medical health, motion detection, human-computer interaction and other fields.

Fluffy poly(vinyl alcohol) fiber filter material was prepared by the centrifugal electrospinning process combined with the opening process, which is used in the field of air filtration. We used a conductive ring to connect the positive high voltage with the centrifugal spinning rotation cup in order to improve the electrostatic loading stability of the centrifugal electrospinning process and make the electric field more concentrated. It can reduce the high voltage attenuation and reduce the voltage deviation from 1.47–1.86 kV to 0.02–0.04 KV. The effects of the loading voltage (0–20 kV) and rotational speed (4000–8000 rpm) of the positive high voltage loading mode on the fiber diameter were investigated. The results show that the voltage loading was beneficial to the formation of fibers with good morphology, especially under the condition of low rotational speed. Moreover, the improvement effect of voltage was more obvious, which can curb the problems caused by insufficient solvent volatilization, such as too thick fiber diameter, fiber dissolution bonding, spot bonding, and so on. In addition, the increase in rotational speed was also beneficial to the refinement of the fiber. We loosened the filter material processed by the centrifugal electrospinning process and explored the effect of the opening process on fibers of different morphologies in order to further promote the application of the centrifugal electrospinning filter material and improve the fluffy degree of the filter material. The results showed that the fiber with good spinning and fewer shift defects has a better opening effect and fluffy degree. Finally, the filtration efficiency of the fiber mat prepared with different process parameters before and after the opening was tested using a filter material tester. The results show that the fiber with few shift defects can effectively reduce the resistance without greatly reducing the filtration efficiency. In fact, the results play a guiding role in the preparation of medium-effect fluffy filter media.