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The purpose of this paper is to illustrate the new technical demands and reliability challenges to printed circuit board (PCB) designs, materials and processes when the transmission frequency increases from Sub-6 GHz in previous generations to millimeter (mm) wave in fifth-generation (5G) communication technology.

The approach involves theoretical analysis and actual case study by various characterization techniques, such as a stereo microscope, metallographic microscope, scanning electron microscope, energy dispersive spectroscopy, focused ion beam, high-frequency structure simulator, stripline resonator and mechanical test.

To meet PCB signal integrity demands in mm-wave frequency bands, the improving proposals on copper profile, resin system, reinforcement fabric, filler, electromagnetic interference-reducing design, transmission line as well as via layout, surface treatment, drilling, desmear, laminating and electroplating were discussed. And the failure causes and effects of typical reliability issues, including complex permittivity fluctuation at different frequencies or environments, weakening of peel strength, conductive anodic filament, crack on microvias, the effect of solder joint void on signal transmission performance and soldering anomalies at ball grid array location on high-speed PCBs, were demonstrated.

The PCB reliability problem is the leading factor to cause failures of PCB assemblies concluded from statistical results on the failure cases sent to our laboratory. The PCB reliability level is very essential to guarantee the reliability of the entire equipment. In this paper, the summarized technical demands and reliability issues that are rarely reported in existing articles were discussed systematically with new perspectives, which will be very critical to identify potential reliability risks for PCB in 5G mm-wave applications and implement targeted improvements.

This study aims to explore the compressive behavior of hollow triply periodic minimal surface (HTPMS) cellular structures by selective laser melting (SLM).

This study presents a design method for gyroid hollow triply periodic minimal surfaces (G-HTPMS) and primitive hollow triply periodic minimal surfaces (P-HTPMS) cellular structures, and SLM technology was applied to manufacture these cellular structures. Compressive behaviors and energy absorption behaviors of hollow cellular structures were researched in this study.

Compared with normal gyroid triply periodic minimal surfaces (G-TPMS) and normal primitive triply periodic minimal surfaces (P-TPMS), the G-HTPMS and P-HTPMS have higher elastic modulus, plateau stress and effective energy absorption under uniaxial compression. The hollow design in HTPMS can enhance the mechanical properties and energy absorption of the cellular structure. Finite element analysis also demonstrates that the hollow design can reduce stress concentration, which improved the compressive curves from a severely fluctuating state to a relatively flat state and reduces fracture. According to compressive behaviors, G-TPMS and G-HTPMS are the bending-dominated cellular structures with strain hardening characteristics, and P-TPMS and P-HTPMS are the stretching-dominated cellular structures with strain softening characteristics.

This research provided a design method for HTPMS, and it was proved that the mechanical properties increased by hollow design inspired by bamboo.

The purpose of this study is focused on the mechanical properties of multi-materials porous structures manufactured by selective laser melting (SLM).

The Diamond structure was designed by the triply periodic minimal surface function in MATLAB, and multi-materials porous structures were manufactured by SLM. Compression tests were applied to analyze the anisotropy of mechanical properties of multi-materials porous structures.

Compression results show that the multi-materials porous structure has a strong anisotropy behavior. When the compression force direction is parallel to the material arrangement, multi-materials porous structure was compressed in a layer-by-layer way, which is the traditional deformation of the gradient structure. However, when the compression force direction is perpendicular to the material arrangement, the compression curves show a near-periodic saw-tooth waveform characteristic, and this kind of structure was compressed consistently. It is demonstrated that the combination with high strength brittle material and low strength plastic material improves compression mode, and plastic material plays a role in buffering fracture.

This research provides a new method for the design and manufacturing of multi-materials porous structures and an approach to change the compression behavior of the porous structure.

We use disaggregated survey data set to investigate the impact of personality traits on the level of education in the USA. We attempt to shed light on the contribution of each of the Big Five personality traits on the education decision made by the individuals.

We use the quantile regression analysis in order to investigate to what extent certain aspects of personality may help an individual to invest in education.

Our findings uncover a significant effect of noncognitive skills on the level of education. It is shown that people with high emotional stability and agreeableness invest in human capital, especially when we move to the higher quantiles of the conditional distribution function. Moreover, we argue that the estimated signs of the traits remain stable across the quantiles, while the relevant curvatures indicate for the first time in the empirical literature, the presence of nonlinear effects. Last, our model survived robustness checks under the inclusion of two aggregated higher-order factors, namely “Alpha” and “Beta.”

Although we used several control variables (e.g. Gender, Age) to address the impact of noncognitive skills on education, special attention should be given to the use of additional socioeconomic indicators such as the skin color of participants, the urbanization rate, the level of unemployment, the level of income, parental education among others. These measures affect the causality driven by the inclusion of certain economic and demographic characteristics and minimize the endogeneity bias drawn from the inclusion of the sample variables. One additional limitation is that the survey-based data refer only to people with higher education (>13 years of study). Therefore, our empirical findings must be tested on a richer sample to capture the effect of personality traits on a broad spectrum of educational stages (e.g. early learning years, primary education, secondary education, etc.).

Our empirical findings add enough new insights to the existing literature. First, we attempt to assess the role of noncognitive skills proxied by the Big Five Inventory (hereafter “BFI”) on the education decision made by the individuals. Second, we provide fresh evidence of nonlinear effects between personality traits and education totally ignored by the existing literature. Our third contribution is to analyze the role of personality in enhancing the importance of investment in higher education as a determinant of individual behavior. In this way, we contribute to the growing field of behavioral economics since the study of noncognitive skills offers a range of new ideas and expanding research opportunities for social scientists (economists, psychologists, sociologists, etc.).