In Case You Missed It
Component Reliability
“Reliability Analysis and Parameter Optimization of Board-Level BGA Packaging Structures under Thermal-Drop Impact Load”
Authors: Yanxi Sun, Zixin Zhen, Xuexia Yang, Miao Zhu and Chao Chang
Abstract: A three-dimensional finite element model of board-level ball grid array (BGA) package structure is established, and numerical calculations are performed based on thermal-drop impact load sequence coupling. The effects of chip thickness, solder ball height, diameter and array on its temperature field distribution, solder ball stress and average impact life are investigated. Optimization schemes were designed using Taguchi quadrature and surface response method. The optimal combination of structural parameters to minimize solder ball peeling stress was determined through mathematical and statistical analysis and regression analysis. (Soldering & Surface Mount Technology, Apr. 2, 2025, https://www.emerald.com/ssmt/article-abstract/37/4/308/1256208/Reliability-analysis-and-parameter-optimisation-of)
Flex Circuit Processing
“Scalable Roll-to-Roll Approach for Encapsulating Long-Length Flexible Printed Circuit Boards”
Authors: Chan-Woo Lee, Eun-Ji Gwak, Doo-Sun Choi, Byoung-Youn Cho and Jun Sae Han
Abstract: The encapsulation process in flexible printed circuit board (FPCB) manufacturing typically involves laminating a flexible copper-clad laminate (FCCL) with a coverlay film, using heat and pressure in methods such as hot press lamination. When they are applied to long-length FPCBs for electric vehicle applications, however, traditional hot press methods face challenges in scalability and productivity. To overcome these challenges, this study proposes a scalable roll-to-roll approach for encapsulating long-length FPCB. This approach enhances scalability to meet the requirement of long-lengthening continuously, but this can lead to incomplete filling in narrow circuit patterns due to insufficient flowability of the B-stage adhesive. To enhance flowability, a roll-to-roll system was developed, incorporating a rubber roll and a steel roll for the adhesive material. The effectiveness of copper width dimensions and process parameters on encapsulation performance was investigated in the experimental analysis according to the rheological and thermomechanical characterizations of the B-stage adhesive. These results were quantified through image analysis and visualized using contour mapping to exhibit the influence of process parameters on the filling area. The reliability and durability of the developed approach were validated through the analysis of adhesive properties and electrical performance. The developed roll-to-roll approach to the encapsulation process enables scalability while ensuring the durability and reliability of the long-length FPCB. (ACS Applied Materials & Interfaces, vol. 17, no. 36, Aug. 21, 2025, https://pubs.acs.org/doi/10.1021/acsami.5c09839)
Sensors
“A Fully-Integrated Flexible In-Sensor Computing Circuit Based on Gel-Gated Organic Electrochemical Transistors”
Authors: Xinyu Tian, Jing Bai, Dingyao Liu, Guangxi Lu and Shiming Zhang
Abstract: Organic electrochemical transistors (OECTs) are promising technologies for biosensing and brain-inspired computing due to their low-power signal amplification and neuron-like behavior. Their manufacturing remains complex, however, especially when fabricated into flexible forms. To address the growing demand for flexible OECTs in wearable bioelectronics, in this work, the authors propose: i) a rapid and low-cost fabrication approach using flexible PCB (FPCB) technology and customized inkjet printing; ii) a non-aqueous gel-gated approach to improve the electrochemical stability of flexible OECTs associated with FPCBs; and iii) the above two approaches help accomplish the following concept: a low-cost, integrated, and in-sensing computing system can be more readily realized with flexible OECT devices. This platform has been validated for scalability, stability, and performance in real-world applications, paving the way for developing low-cost, flexible, multifunctional OECT systems. (npj Flexible Electronics, vol. 9, no. 90, 2025, https://www.nature.com/articles/s41528-025-00472-x)
Solder Migration
“Electromigration in Eutectic Gold-Tin (80Au20Sn-wt%) Solder Joints”
Authors: Whit Vinson and David Huitin
Abstract: Eutectic gold-tin solder joints (80Au20Snwt%) with a diameter of 300μm diameter were 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 500hr. One coupon type created a linear electric current pathway through two lengths of 254μm-diameter copper wire connected by a single AuSn joint. The other coupon type daisy-chained four AuSn 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 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, Sept. 9, 2025; https://link.springer.com/article/10.1007/s11664-025-12344-1)