In Case You Missed It

Thermal Dynamics

“Dynamic Thermal Response and Flow Behavior of a Zigzag Printed Circuit Heat Exchanger under Transcritical Conditions”

Authors: Yatian Zhao, Kai He, Hongyue Zhao and Hongkang Liu

Abstract: Studies on the dynamic response characteristics of printed circuit heat exchangers (PCHEs) are rather limited. The mechanisms by which channel geometry and operating pressure affect dynamic behavior remain unclear, which indicates that the structural modifications could easily introduce new challenges. In this study, three-dimensional transient simulations are performed to analyze the thermohydraulic response of a zigzag-channel PCHE subjected to inlet temperature step disturbances (from 335K to 415K) near the pseudo-critical region. Compared to the straight channel, the zigzag configuration exhibited better cooling performance under steady-state conditions, as indicated by a lower outlet temperature. Under transient conditions, the zigzag channel demonstrated better dynamic response performance than the straight channel, shortening the outlet temperature response time by 2.58 sec. This improvement is primarily attributed to stronger secondary flow vortices that accelerate heat transfer during transient thermal disturbances. These effects are especially significant when the fluid shifts between subcritical and supercritical states, where rapidly changing fluid properties enhance mixing and promote more efficient heat transfer. Additionally, the dynamic response of the PCHE under different operating pressures (7.6MPa,8.1Mpa,8.6 MPa) was investigated. Interestingly, although higher pressure enhances steady-state cooling performance, it results in a longer dynamic response time – delayed by 4.05 sec – due mainly to reduced thermal diffusivity and diminished heat transfer effectiveness in the central flow region under elevated pressures. These findings highlight the dynamic advantages of zigzag channels and reveal the tradeoffs between pressure and responsiveness, offering guidance for optimizing PCHEs under transient conditions involving both subcritical and supercritical operations. (Applied Thermal Engineering, vol. 281, part 2, Dec. 15, 2025; https://doi.org/10.1016/j.applthermaleng.2025.128695)

Plating

“Electrochemical and ATR-SEIRAS Investigation of Microvia Filling Performance of Amino Functionalized N Heterocyclic Levelers”

Authors: Yaokun Sun, et al.

Abstract: This study investigates the feasibility of 2-mercaptopyrimidine (MPD), 2-thiocytosine (TC), and 4,6-diamino-2-thiopyrimidine (DTP) as novel levelers for copper electroplating in microvia filling applications. Galvanostatic measurements, combined with in situ attenuated total reflectance surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) and density functional theory (DFT) calculations, were employed to elucidate the adsorption behaviors and interfacial mechanisms of the additives. Results indicate that while all three molecules adsorb onto copper surfaces via Cu-S and Cu-N coordination, TC and DTP form more stable adsorption configurations due to additional amino group interactions. MPD, lacking amino functionality, exhibited significant desorption at negative potentials. Microvia filling experiments demonstrated that MPD fails to achieve effective leveling, whereas trace amounts (1mg/L) of TC and DTP enabled bottom-up superfilling with filling efficiencies of 96.6% and 101.5%, respectively. These findings highlight the critical role of amino groups in enhancing adsorption stability and deposition uniformity, offering valuable insights for the molecular design of high-performance electroplating additives. (Electrochimica Acta, vol. 542, Dec. 1, 2025)

Solder Materials

“Electromigration in Eutectic Gold-Tin (80Au20Sn-wt%) Solder Joints”

Authors: Whit Vinson and David Huitink

Abstract: Eutectic gold-tin solder joints (80Au20Snwt%) with a diameter of 300μmwere subjected to electromigration (EM) conditions of 10,000–20,000A/cm² in the ambient temperature range of 125°–215°C. The present work examines a set of 36 experimental test runs using two different test coupons (18 runs with each coupon type and a total of 90 joints tested). Seven of the 36 coupons survived the maximum test duration period of 500 hr. One coupon type created a linear electric current pathway through two lengths of 254μm-diameter copper wire connected by a single gold–tin joint. The other coupon type daisy-chained four gold–tin joints together in series in a flip-chip configuration using two Rogers 4003C printed circuit boards with electroless nickel immersion gold (ENIG)-finished 2 oz. (c.56.6g) copper traces and a 240μm solder mask-defined (SMD) pads. The time to EM failure (TTEF) was recorded for each experimental run, demonstrating reduced lifetime with increasing current density and/or ambient temperature. To account for the joule heating associated with the high current densities used in this study, temperature coefficient of resistance measurements (TCR) were carried out for both sample groups. To describe the TTEF data, a lifetime model for 80Au20Sn-wt% joints combining the experimental testing conditions with TCR data has been developed. Post-failure analysis (PFA) on the tested solder joints shows several morphological phenomena occurring in the gold–tin joints under EM conditions, including solder migration into the trace, spinodal decomposition, phase coarsening and phase separation. (Journal of Electronic Materials, vol. 54, Sept. 9, 2025; https://link.springer.com/article/10.1007/s11664-025-12344-1)

Sustainable Electronics

“Printed Circuit Board Substrates Derived from Lignocellulose Nanofibrils for Sustainable Electronics Applications”

Authors: Yuliia Dudnyk, Pavel Kulha, Václav Procházka, Gustav Nyström and Thomas Geiger

Abstract: This study investigates lignocellulose nanofibrils (LCNF) as a sustainable alternative material for printed circuit board substrates, demonstrating an application through the development of an eco-friendly computer mouse demonstrator. LCNF is derived from lignin-rich cellulose pulp, a side-stream product of biorefinery processes, combining the natural strength of cellulose fibrils with lignin to enhance mechanical and electrochemical properties. The research outlines the process of fibrillating lignin-rich cellulose pulp at 10kW/h per kg into LCNF, followed by thermal and pressure treatment (at Δp = 50 – 1500 kN, ΔT = 30°–120°C) to achieve a rigid PCB substrate. Comprehensive characterization of the LCNF substrate included assessments of its mechanical properties (flexural and tensile testing), dimensional stability, electrical properties, surface uniformity and thermal conductivity. The LCNF PCB was integrated in a computer mouse demonstrator featuring inkjet printing of circuit layouts and electronic component assembly, while the mouse housing was designed and 3D-printed using eco-friendly Wood PLA filament. Electrical properties characterization of the printed circuit and resulting functionality of the computer mouse showcases a sustainable approach to eco-electronics using wood-derived materials. This study underscores the potential of wood-derived nanomaterials like LCNF to reduce electronic waste (e-waste) associated with conventional PCB materials and promote the development of a more eco-friendly electronics, contributing to sustainable, high-performance ecoPCBs and advancing green technology. (Scientific Reports, vol. 15, 2025; https://www.nature.com/articles/s41598-025-91653-1)