The reliability of lead-free solder joints on flexible PCB has created significant new challenges in the industry, especially in automotive electronics, and possibly for future wearable electronics.In this paper, the submodeling technique was used to construct the finite element model of the rigid-flexible printed circuit board (rigid-flexible PCB) for a MEMS pressure sensor subjected to combined temperature cycle and random vibration loadings. During all the experiments, the electrical signals of each specimen were continuously monitored using an event detector. One advantage of this method is that any individual soldering interconnect failure will result in the diagnostic signal of the circuit, which could be detected in real time. The influence of vibration frequency and acceleration on the vibration fatigue life of solid joints was investigated.The research results are helpful to effectively characterize the performance of the MEMS sensors under combine thermal cycling test and vibration test. Two kinds of land shapes and two kinds of PCB assemblies were selected. The solder joint is sliced and the crack on the cross section of solder joint was observed. Results of finite element modeling analysis were consistent with the experimental results. Two design parameters have been identified in our research as being important to soldering usage in automotive environments: pad type (teardrop vs. non-teardrop) and pad size (big vs. small, matching size for Cu-wire and pad). Experimental results also showed that the solder joint with big land shape presented a relatively good thermal fatigue resistance.
The unprecedented global pandemic known as COVID-19 caused by SARS-CoV-2 has a profound impact on human life and health, economy and society. Since the outbreak, tremendous effort has been put forth to expand our capacity to diagnose this deadly virus, because accurate detection is essential to effectively combat the epidemic. Numbers of reports have focused on whether the detection methods are sensitive and accurate enough [1]. Little information on the critical first step of detection, sample preservation, is available. At present, there are various of virus Preservation Solutions (PS) on the market, which are used for the preservation of swab samples in nucleic acid detection of SARS-CoV-2. When screening or testing for SARS-CoV-2, pharyngeal swab or nasal swab should be put into PS. Before nucleic acid extraction, the sample may stay in the protective solution for several hours or days. If the sample is not effectively protected in the preservation solution, resulting in the degradation of virus nucleic acid then false negative will occur in the downstream detection process [2]. Therefore, the protection ability to virus RNA of PS is critical important to the reliability of nucleic acid detection results.
Abstract. In this paper, a dynamic simulation model of flap mechanism is established by using Simulink and simultaneous constraint method. Based on this model, the regularity and volatility of kinematic parameters' error is analyzed under the influence of comprehensive error, the position of flap deflection angle maximum deviation and the maximum drive torque are found. Then, under the dynamic analysis, using vector projection method to integrate the amount of wear, and the reliability of flap deflection accuracy and the reliability of flap seizure are calculated by Monte Carlo method under abrasive wear and synthetic error condition.
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