This review covers developments in ‘Atomic Spectrometry’. It covers atomic emission, absorption, fluorescence and mass spectrometry, but excludes material on speciation and coupled techniques which is included in a separate review. It should be read in conjunction with the other related reviews in the series.1–6 A critical approach to the selection of material has been adopted, with only novel developments in instrumentation, techniques and methodology being included. Developments worthy of note include photochemical and electrochemical methods of vapour generation, single particle analysis using ICP-MS and the development of new methods for direct plasma generation in liquid samples. The use of MC-ICP-MS continues to grow in importance for isotope ratio measurements in fields as diverse as geochronology, nuclear forensics and biomedical research. Laser-based methods are also important in many fields, particularly for direct and stand-off analysis of solid samples.

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Atomic spectrometry update: review of advances in atomic spectrometry and related techniques

The consumer electronics devices continue to develop towards ultra-thin, high-density and miniaturization. Advanced mold flow simulation analysis before the actual experiment will help to predict and understand the potential risks of Epoxy Molding Compound (EMC) filling and then effectively promote mold design and material selection. However, the contribution of mold flow simulation to EMC material evaluation is still insufficient. One of the main reasons is that mold flow simulation requires a large number of material parameters, so it is difficult to analyze the material by traditional design of experiment (DOE) methods. In this paper, we investigate a structure for an ultra-thin and fine-pitch package, and uses one commercial EMC material to study its mold flow filling process in Modex3D software. The changing of temperature, shear rate, curing degree and viscosity during the filling process are analyzed in detail. In addition, based on detailed analysis of the viscosity equations and curve, the influences of temperature, filling time, viscosity, gel point and curing kinetics parameters on filling state are discussed in depth. This research is expected to provide theoretical guidance for improving the filling state in ultra-thin fine-pitch devices in terms of material design and process control.

Mold Flow Simulation Analysis of Molded Underfill in an Ultra-thin High-Density Package

A motor core is formed by stacking iron sheets on top of each other. Traditionally, there are two stacking methods, riveting and welding, but these two methods will increase iron loss and reduce usage efficiency. The use of resin is the current developmental trend in the technology used to join iron sheets, which has advantages including lowering iron loss, smoothing magnetic circuits, and generating higher rigidity. The flow behavior of resin in gluing technology is very important because it affects the dipping of iron sheets and the stacking of iron sheets with resin. In this study, a set of analytical processes is proposed to predict the flow behavior of resin through the use of computer-aided engineering (CAE) tools. The research results are compared with the experimental results to verify the accuracy of the CAE tools in predicting resin flow. CAE tools can be used to predict results, modify modules for possible defects, and reduce the time and costs associated with experiments. The obtained simulation results showed that the filling trend was the same as that for the experimental results, where the error between the simulation results for the final dipping process and the target value was 0.6%. In addition, the position of air traps is also simulated in the dipping process.

Mold Flow Analysis of Motor Core Gluing with Viscous Flow Channels and Dipping Module.

To solve the problem in which the output power and wavelength of semiconductor lasers in fiber optic sensing systems are easily affected by the drive current and temperature, a high-precision current drive and temperature control system was developed in this study. The embedded system was used to provide a stable drive current for the semiconductor laser through closed-loop negative feedback control; moreover, some measures, such as linear slow-start, current-limiting protection, and electrostatic protection, were adopted to ensure the stability and safety of the laser’s operation. A mathematical model of the temperature control system was constructed using mechanism analysis, and model identification was completed using the M sequence and differential evolution (DE) algorithms. Finally, the control rules of the fuzzy proportional integral differentiation (PID) algorithm were optimized through system simulation to make it more suitable for the temperature control system designed in this research, and the accurate control of the working temperature of the semiconductor laser was realized. Experimental results showed that the system could achieve a linearly adjustable drive current in the range of 0–100 mA, with an output current accuracy of 0.01 mA and a temperature control accuracy of up to 0.005 °C.

https://www.mdpi.com/1424-8220/22/24/9989/pdf?version=1671363437

High-Precision Semiconductor Laser Current Drive and Temperature Control System Design

This review covers advances in atomic spectrometric techniques, including atomic emission, absorption, fluorescence and mass spectrometry. Material on speciation and coupled techniques is not covered as this is included in a separate ASU review. 

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At present, System in Package (SiP) is getting more and more applications in power packages. Due to the complexity of the packages, the molding process becomes crucial for the yield and reliability of the products. During the transfer molding process, the packaging processes of the packages may introduce assembly defects, such as void, wire sweep, warping, etc. To determine the main factors is one of the most important measures to eliminate and prevent these defects.In this paper, 3D Molding flow simulation for the SiP package is conducted by using the Moldflow software with the aim to predict the location of the void and weld line during the plastic package process. The influence of gate design on process-induced defects and other reliability issues was studied. The results show that the filling of different gate locations in the package will produce cavitation defects at different locations. A gate design with fewer corners in the injection direction will produce fewer cavitation. Increasing the number of gates will reduce air pockets at the corners, but will cause more air pockets near the weld line. When the gate position is perpendicular to the top surface of the chip, less weld marks are generated. The flow front will produce weld marks after being blocked. When the number of gates increases, the area of the flow front increases and the number of weld lines increases significantly.

Mold Flow Analysis of a SiP Package for Power Management

In semiconductor lasers, chip heat dissipation is a hot topic in current research. The increase in chip temperature will not only affect the service life of the laser, but also the thermal stress will reduce the reliability of the laser. To solve this problem, this research starts with the bonding layer between the laser chip and the substrate, uses nano-silver solder paste with high thermal conductivity as the bonding material, and uses the finite element analysis method to simulate the heat dissipation and stress distribution of the semiconductor laser at room temperature. At the same time, under the different heat consumption of the laser chip, the heat dissipation performance of the nano-silver solder and the commonly used AuSn and In solders was compared. The results show that the use of nano-silver solder paste is more conducive to the heat dissipation of the laser chip, and can effectively reduce the thermal stress of the laser chip. The research method proposed in this paper illustrates the feasibility of using nano-silver solder paste as the bonding material between the laser chip and the heat sink, and provides a reference for the design of semiconductor laser packaging.

Simulation Study on Thermal Characteristics and Thermal Stress of Semiconductor Laser Package

A self-consistent two-dimensional fluid model is employed to investigate the coaxial–coplanar dielectric-barrier discharge (DBD) excited by the sinusoidal voltage in atmospheric helium. Simulation results show that there are two current pulses in the positive half cycle, but only one in the negative half cycle. The discharge is transformed from the Townsend-like mode, through the glow-like mode, and back to the Townsend-like mode in both the positive and negative half cycles, during which the electric field line exhibits an arc-shape profile due to the configuration of coaxial–coplanar electrodes. In the glow-like mode, the cathode fall is located near the inner edge of the ground electrode at the first positive current peak, but close to the outer edge of the ground electrode at the second positive current peak. At the negative current peak, the cathode fall is distributed near the outer edge of the high voltage electrode. Since the instantaneous anode and the instantaneous cathode are on the same side of the discharge space, the dielectric layer is simultaneously covered by positive and negative surface charges due to the movement of charged particles. It is also found that the surface charge density changes significantly on the dielectric layer facing the electrodes. A further study reveals that a stronger discharge always occurs in the central circular area and an alternately complementary discharge takes place in the periphery ring area in the positive half cycle due to the activator–inhibitor effect. This feature is helpful for producing uniform plasma in a whole cycle of DBD.

https://aip.scitation.org/doi/pdf/10.1063/5.0089080

Numerical simulation of coaxial–coplanar dielectric-barrier discharge in atmospheric helium

Comparative study on the copper plasma confined with upward and downward conical cavities in laser-induced breakdown spectroscopy

Discharge-assisted laser-induced breakdown spectroscopy (D-LIBS) represents a highly promising technique in trace detection. However, it consumes large amounts of energy causing severe environmental pollution. Herein, we demonstrate a modulation approach based on ion dynamics to reduce energy costs and environmental hazards. This modulation traps and confines numerous charged particles in an effective discharge space. It then maintains the charged particle electric-drift dynamics in the millisecond timescale, largely facilitating electric energy coupling to laser plasma and prolonging plasma lifetime. Compared with conventional D-LIBS, both the electric energy and limit-of-detection are reduced by one order of magnitude, while maintaining over two orders of magnitude signal enhancement. Combined with optimized wavelet transform de-noising, the sensitivity is approximately two orders of magnitude higher than recently reported levels for typical elements. Examining electric characteristics, plasma dynamics, and signal stability further verifies the modulation validity. These low-harm, low-power, and high-sensitivity advantages pave the way for high-efficiency applications of D-LIBS in rapid and real-time analysis. 

Yi Duan

Papers

Mold Flow Analysis of a SiP Package for Power Management

Simulation Study on Thermal Characteristics and Thermal Stress of Semiconductor Laser Package

Numerical simulation of coaxial–coplanar dielectric-barrier discharge in atmospheric helium

Comparative study on the copper plasma confined with upward and downward conical cavities in laser-induced breakdown spectroscopy

Large modulation of ion dynamics for discharge-assisted laser-induced breakdown spectroscopy