In Case You Missed It
Solder Materials
“Effect of Sb and Ag Addition and Aging on the Microstructural Evolution, IMC Layer Growth, and Mechanical Properties of Near-Eutectic Sn-Bi Alloys”
Authors: Hannah N. Fowler, et. al.
Abstract: Low-melting-point Sn-Bi solder joints (melting point: 139°C) show remarkable resistance to damage accumulation during aggressive thermal cycling. In this study, the authors used isothermal aging at 85°C of near eutectic Sn-Bi solder joints to determine the effect of Sb in solid solution and Ag3Sn intermetallic on microstructural evolution and the resulting mechanical properties to explain the thermal cycling behavior. Most importantly, the Sb in solid solution in these alloys resulted in higher strength and improved creep resistance compared to eutectic Sn-Bi. In contrast to SnPb and SnAgCu Pb-free alloys, all the near-eutectic SnBi alloys tested showed significant age hardening. In both unaged and aged conditions, both Sb and Ag additions individually increased saturation stress of the eutectic SnBi solder joint, but Ag had a more significant effect. However, when both Sb and Ag were added to eutectic Sn-Bi, the saturation stress was lower than when 1 wt.% Ag alone was added. In terms of relative behavior, the Sb-free 42SnBi1Ag aged for 250 hr. had the highest saturation stress of all tested alloys, while as-reflowed eutectic SnBi had the lowest saturation stress. These results suggest that the alloy design strategy for SAC alloys; i.e., assuming that the effects of individual alloying elements are additive and independent, is not valid when Sb is added to SnBi low-temperature solder. (Journal of Electronic Materials, December 2023, https://doi.org/10.1007/s11664-023-10866-0)
Stencil Printing
“Effect Of PVD-Coated Wall Aperture Roughness on the Life Span of Fine-Pitch Stencil Printing”
Authors: Mohamed Sunar, et. al.
Abstract: This paper aims to investigate the effect of physical vapor deposition (PVD)-coated stencil wall aperture on the life span of fine-pitch stencil printing. The fine-pitch stencil used in this work is fabricated by electroform process and subsequently nano-coated using the PVD process. Stencil printing process was then performed to print the solder paste onto the PCB pad. The solder paste release was observed by solder paste inspection (SPI) and analyzed qualitatively and quantitatively. The printing cycle of up to 80,000 cycles was used to investigate the life span of stencil printing. The finding shows the performance of stencil printing in terms of solder printing quality is highly dependent on the surface roughness of the stencil aperture. PVD-coated stencil aperture can prolong the lifespan of stencil printing with an acceptable performance rate of about 60%. (Soldering & Surface Mount Technology, January 2024, https://doi.org/10.1108/SSMT-05-2023-0025)
Wave Modeling
“A Segmentation Approach for Predicting Plane Wave Coupling to PCB Structures”
Authors: Shengxuan Xia, et. al.
Abstract: Evaluating the far-field radio frequency (RF) susceptibility of electronic devices often depends on extensive testing or full wave simulations. These methods are effective when complete system information is available but require substantial time and resources to evaluate a large number of variations in system configurations, where trace routings, IC package styles, trace terminations, arrival angle, and polarization of incoming wave, etc., vary from one configuration to another. The goal of the study was to develop simulation techniques for studying the statistical characteristics of coupling to typical PCB structures. Simulation time can be reduced by breaking the structure into small segments, determining the coupling and transmission characteristics of each segment analytically or in a full-wave model, and then determining the coupling to the overall structure by assembling the individual segments in a circuit simulation. Reusing premodeled segments of commonly occurring structures (e.g., IC package, trace, etc.) allows estimates with minimal computational effort even for a complicated PCB design. Simulation time is estimated to improve by a factor of 40 or more over traditional full-wave modeling using this approach. This methodology enables the analysis of statistical electromagnetic coupling to random PCB geometries. (IEEE Transactions on Electromagnetic Compatibility, January 2024, 10.1109/TEMC.2024.3349911)
Wireless Power Transfer
“Improved Design of PCB Coil for Magnetically Coupled Wireless Power Transfer”
Authors: You Fu, et. al.
Abstract: In recent years, wireless power transfer (WPT) has progressed rapidly in both theory and commercialization. However, existing research into WPT coil design for low-power devices to mitigate the coil offset is limited. A dual-layer printed circuit board (PCB) structure is proposed in this paper to mitigate the coil offset while retaining manufacturing simplicity for practical uses. Specifically, the impacts of key geometric parameters on the coil quality factor and coupling coefficient are analyzed through models and simulations. Equivalent PCB coils were formed for mutual inductance models, and four basic compensation circuits were analyzed. The impacts of changes in coil thickness, line width, turn spacing, and number of turns on the quality factor of PCB coils were analyzed with a fixed outer diameter of the coil. Eleven types of PCB coils were manufactured to verify the simulation results. The offset transmission efficiency can reach 46.6% with an output power of 14.4W. The PCB coil with improved design could offer remarkable improvements in the WPT system for low-power electronic devices. (Electronics, January 2024, https://doi.org/10.3390/electronics13020426)
