Technical Abstracts
In Case You Missed It
Electronic Materials
“Highly Stretchable Multilayer Electronic Circuits Using Biphasic Gallium-Indium”

Authors: Shanliangzi Liu, Dylan S. Shah and Rebecca Kramer-Bottiglio

Abstract: Development of sophisticated stretchable circuits requires new materials with stable conductivity over large strains, and low-resistance interfaces between soft and conventional (rigid) electronic components. To address this, the authors introduce biphasic Ga-In, a printable conductor with high conductivity (2.06 × 106 S m−1), extreme stretchability (>1,000%), negligible resistance change when strained, cyclic stability (consistent performance over 1,500 cycles) and a reliable interface with rigid electronics. A scalable transfer-printing process is employed to create various stretchable PCB assemblies that maintain their performance when stretched, including a multilayer LED display, an amplifier circuit and a signal conditioning board for wearable sensing applications. The compatibility of biphasic Ga-In with scalable manufacturing methods, robust interfaces with off-the-shelf electronic components and electrical/mechanical cyclic stability enable direct conversion of established circuit board assemblies to soft and stretchable forms. (Nature Materials, Feb. 18, 2021)

Fabrication Processes
“Periodic Pulse Plating of Mid-Aspect Ratio Printed Circuit Boards for Enhanced Productivity”

Author: Carmichael Gugliotti, Rich Bellemare, Andy Oh and Ron Blake

Abstract: Pulse plating of copper has typically found use in the plating of difficult high-aspect-ratio printed circuit boards. Its ability to provide throwing power deep within through-holes with aspect ratios as high as 30:1 is well-established. This technology has long been thought of as a high-technology, high-cost, specialty process applicable only to high-end products. This paper discusses the advantages that pulse plating offers over conventional DC copper plating in high-volume production applications for panels with aspect ratios of up to 12:1. These advantages are reduced plating time, increased throughput, and reduced plated copper thickness on the panel surface, while meeting minimum in-hole copper thickness requirements. (SMTA Journal of Surface Mount Technology, vol. 33, no. 2, June 2020)

Printed Circuit Design
“Analysis of Crosstalk in High Speed and High Frequency Printed Circuit Board”

Authors: Avali Ghosh, Sisir Kumar Das and Annapurna Das

Abstract: Numerical analysis of crosstalk between two traces in a printed circuit board is presented using the method of moments (MoM). In the high-frequency range, the attenuation constant is neglected in the theory for its very small values. The width of the trace is accurately determined for the trace impedance of 50 ohm from the charge distribution on the traces without using an approximated empirical formula. Line capacitances are determined from the total charge on the conductors and the line potentials. The coupling capacitance and inductance are determined from in-phase and out-of-phase excitations between the traces. Crosstalk interference is calculated from these coupling parameters. Results of crosstalk obtained from the above technique are verified by comparing with those obtained from four other methods: 1) Ansoft HFSS software, 2) even mode and odd mode analysis, 3) empirical formulae of parasitic elements, and 4) measurements using a vector network analyzer. All the results agreed well. The results obtained by using the method of moment technique are more stable, reliable and accurate among all the described different methods. This paper shows that the analytical method using MoM is a useful tool for predicting crosstalk interference in PCB without using expensive simulation software. (International Journal of Electronics, Jan. 19, 2021)

Solder Joint Reliability
“An Investigation on Function of Current Type on Solder Joint Degradation in Electronic Packages”

Authors: Wenhui Cai, Fei Huang, Kai Liu and Mohammed Alaazim

Abstract: In real applications, several alternating currents (AC) may be injected into electronic devices. This study aims to analyze their effects on the lifetime of the solder joints and, consequently, shed light on these effects at the design phase. The authors investigated current waveform shapes on the performance and reliability of the solder joints in an electronic package. Three common and extensively used current shapes in several simulations and experiments were selected to study their effects on the solder joint performance. The results demonstrate a severe thermal swing and stress fluctuation in the solder joint induced in the case of triangle current type because the critical states lack any relaxation time. In fact, the stress intensification in the solder under application of the triangle current type has been shown to contribute to increasing brittle intermetallic compounds. An accelerated increase of on-state voltage of power semiconductor was also observed in the under application of the triangle current type. (Soldering & Surface Mount Technology, Sept. 23, 2020)

This column provides abstracts from recent industry conferences and company white papers. Our goal is to provide an added opportunity for readers to keep abreast of technology and business trends.