Search Results (8)

Most electromagnetic metasurfaces only control a single property of electromagnetic waves, such as the phase, amplitude, polarization or frequency, leading to a shortage in capacity and security in communication and a decrease in radar imaging efficiency. By switching the states of four PIN diodes soldered between adjacent resonant arms, cross-polarization and co-polarization reflected waves both with a 1-bit phase can be implemented. The simulation results demonstrate that the proposed metasurface operates within a frequency band of 5.7 GHz to 5.88 GHz, covering ISM 5.8 GHz. Within its operational frequency range, in the cross-polarization reflection case, the losses of the 1-bit phase reflected wave are from 1 dB to 1.5 dB, with a high polarization conversion rate exceeding 91% and even reaching 99%. For the co-polarization reflection case, the losses of the 1-bit reflected wave are from 0.3 dB to 2 dB, and the polarization conversion is almost 100%. The phase difference of the reflected wave in both cases can be realized as about 180°, which satisfies the 1-bit phase requirement for building a good property of beam steering. Upon constructing a 10 × 10 small array, the cross-polarized reflection beam can be steered within the range of elevation angle from 0° to 45° and the elevation angle from 0° to 30° in the co-polarized reflection case. Full article

This study presents a method to analyze the electrical resistance of planar contacts. The method can determine whether the contact resistance of the joint exhibits linear or non-linear behavior. By analyzing the current distribution over a planar contact, it can be determined whether an area-based contact resistance is justified or if other parameters define the contact resistance. Additionally, a quantitative evaluation of the factors that affect the measurement accuracy, including the positioning, the measurement equipment used, and the influence of the current injection on the sense pin was conducted. Based on these findings, the electrical contact resistance and the mechanical ultimate tensile force of a silver-filled epoxy-based adhesive are analyzed and discussed. The layer thickness and the lap joint length were varied. Overall, the investigated adhesive shows a low contact resistance and high mechanical strength of the same magnitude as that of well-established joining techniques, such as welding, press connections, and soldering. In addition to evaluating the mechanical and electrical properties, the electric conductive adhesive underwent an economic assessment. This analysis revealed that the material costs of the adhesive significantly contribute to the overall connection costs. Consequently, the effective costs in mass production are higher than those associated with laser beam welding. Full article

The electronic devices suffer great vibration and temperature fluctuation in an airborne environment, which has been always a big challenge for reliability design. In this paper, the reliability of the complex electronic components for airborne applications under a thermal cycling test, random vibration and combined loading has been investigated by experiment tests and finite element simulation. The fatigue life and failure location under different loadings have been compared and discussed, respectively. The results indicated that the combined fatigue life was much shorter than a single-factor experiment. The failed solder joints mostly appeared at the interface between the solder and the copper pad on the component side and the location was at the corner for all three harsh environment tests. Nevertheless, several differences could be observed. For temperature cycling, all the specimens failed due to the increase in daisy chain resistance rather than the open circuit for the combined loading test. That is because the degeneration of the solder caused by temperature variation led to lower stress levels and fatigue life. Moreover, the pins fractured at the welding regions have been observed. The modified Coffin—Manson model, Miner’s linear fatigue damage criterion and Steinberg’s model and rapid life-prediction approach were used to predict the fatigue life under temperature cycling, random vibration and combined loading, respectively. With these methods, the accurate numerical models could be developed and validated by experiment results. Thanks to the simulation, the design time could be effectively shortened and the weak point could be determined. Full article

Recently, 3D packaging has been regarded as an important technical means to continue Moore’s Law. However, excessive stacking will increase the longitudinal dimension, and one chip with high-density bondings packaging is still needed. Thus, it naturally places higher demand on thermal cycling reliability due to the decreased joint size to satisfy high-density packaging. In this work, the nano-Al₂O₃ (1 wt.%) modified Sn-1 wt.% Ag-0.5 wt.% Cu low-Ag solder was applied as a solder sample to evaluate the associated thermal cycling reliability. The investigated results revealed that the nano-Al₂O₃ modified solder did present enhanced thermal cycling reliability, as evidenced by the delayed microstructure coarsening and the inhibited atom inter-diffusion at interface caused by the adsorption of nano-Al₂O₃ on grain surfaces, and the resultant pinning effect. Worthy of note is that the potential of the newly developed nano-Al₂O₃ modified solder for high-density packaging applications (e.g., BGA, QFN, and CCGA) was evaluated based on the Finite Element Modeling. Full article

In the electronics industry, it is common to measure the positions of the solder pins of electrical connectors from the bottom using the automated optical inspection (AOI) technique. However, the pins’ surfaces facing the camera of the AOI system may generate image noises, leading to inaccurate measurement results. The objective of the paper is to develop a machine vision system with an algorithm to measure the pin position from the side. Two images must be captured in different view directions so that the algorithm can use the information on the images to calculate the positions of the pins. Comparing the results obtained using the proposed method and those obtained using a 2D vision measuring machine to measure the positions from the bottom, we found that the maximum difference in the results was 0.03 mm. The technique presented in the paper can provide an alternative solution for measuring the positions of the solder pins of electrical connectors or similar components if measurement from the bottom is not feasible. Full article

Current challenges in printed circuit board (PCB) assembly require high-resolution deposition of ultra-fine pitch components (<0.3 mm and <60 μm respectively), high throughput and compatibility with flexible substrates, which are poorly met by the conventional deposition techniques (e.g., stencil printing). Laser-Induced Forward Transfer (LIFT) constitutes an excellent alternative for assembly of electronic components: it is fully compatible with lead-free soldering materials and offers high-resolution printing of solder paste bumps (<60 μm) and throughput (up to 10,000 pads/s). In this work, the laser-process conditions which allow control over the transfer of solder paste bumps and arrays, with form factors in line with the features of fine pitch PCBs, are investigated. The study of solder paste as a function of donor/receiver gap confirmed that controllable printing of bumps containing many microparticles is feasible for a gap < 100 μm from a donor layer thickness set at 100 and 150 μm. The transfer of solder bumps with resolution < 100 μm and solder micropatterns on different substrates, including PCB and silver pads, have been achieved. Finally, the successful operation of a LED interconnected to a pin connector bonded to a laser-printed solder micro-pattern was demonstrated. Full article

The pin-in-paste technology is an advancing soldering technology for assembling complex electronic products, which include both surface-mounted and through-hole components. A computational fluid dynamics model was established to investigate the stencil printing step of this technology, where the hole-filling by the solder pastes is the most critical factor for acquiring reliable solder joints. The geometry of the transient numeric model included the printing squeegee, the stencil, and the through-holes of a printed circuit board with different geometries and arrangements. A two-phase fluid model (solder paste + air) was applied, utilizing the Volume of Fluid method (VoF). The rheological properties of the solder paste were addressed by an exhaustive viscosity model. It was found that the set of through-holes affected the flow-field and yielded a decrease in the hole-filling if they were arranged in parallel with the travelling direction of the printing squeegee. Similar disturbance on the flow-field was found for oblong-shaped through-holes if they were arranged in parallel with the squeegee movement. The findings imply that the arrangement of a set of through-holes and the orientation of oblong-shaped through-holes should be optimized even in the early design phase of electronic products and during the set of assembly processes. The soldering failures in pin-in-paste technology can be reduced by these early design-phase considerations, and the first-pass yield of electronic soldering technologies can be enhanced. Full article

Enhancing the heat transfer surface by usage of cellular metal structures, such as foams or wire structures, might allow enlarging the surface area, increasing the heat transfer coefficients, decreasing the material utilization, and enabling the flexibility of different geometrical dimensions. However their manufacturing and assembling in a large heat exchanger for performance testing and optimizing can be costly. Therefore a test rig was constructed for experimental characterization of heat transfer surface area enhancements. Heat exchanger samples with dimensions in the centimeter range can be measured. The fluid flow and heat transfer features of a micro pin fin wire structure made from copper by soft-soldering were experimentally characterized under steady-state forced air convection. The results are compared to performance characteristics of louvered fins. Heat transfer coefficients of the pin fins are twice as high as for the louvered fins. The relative expanded uncertainty of the Nusselt number is ±7%. Full article