High-frequency 5G wireless infrastructure requires a new approach to PCB manufacturing

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Author: Benny Solomon
Date: July 2018
From: EE-Evaluation Engineering(Vol. 57, Issue 7)
Publisher: Endeavor Business Media
Document Type: Article
Length: 1,722 words
Lexile Measure: 1630L

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Much has been written about the impending global rollout of 5G wireless infrastructure, and the profound impact that it will have on everything from mobile phone connectivity and fixed-wireless services to transportation, industrial, and entertainment applications and beyond. Providing the ability to deliver 10X faster data rates--with a roadmap to 100X faster speeds--and the capacity to handle 1,000X more data traffic, 5G will enable a unified connectivity mesh encompassing people, autonomous vehicles, IoT devices, industrial machines, and civil infrastructure.

With faster download speeds comes lower latency, and this is essential in applications where near-real-time system responsiveness is required. This will affect the seamlessness of augmented-reality and virtual-reality (AR/VR) experiences, the precision of machine-to-machine (M2M) communications, and the productivity of industrial infrastructure. Perhaps most importantly, ultralow-latency 5G wireless will enable safer transportation via improved connectivity among autonomous vehicles and roadway/airway sensors--where passenger safety is concerned, every millisecond of vehicle response time is critical.

For these 5G-driven applications, the margin for error is impossibly small, and yet the risk of system malfunction or communication failure grows exponentially larger with every new electronic device connected to the network. At the device level, this means that every individual PCB must be subjected to higher standards for performance and quality to help ensure real-time 5G communication continuity. While different technologies and processes are being developed to address these challenges, PCB suppliers are rethinking their production processes with an eye toward new manufacturing systems that improve quality assurance while simultaneously boosting production efficiency.

Signal-integrity challenges

The higher frequencies inherent to 5G pose a key challenge to PCB manufacturing, and this challenge is compounded by the shrinking form factors of electronic devices. The high-density interconnects (HDIs) designed into these compact devices require thinner traces to maximize I/O while minimizing system size. But finer lines can introduce increased risk of signal degradation. If the line's physical characteristics--for example, width of the top and bottom--vary in any way from the intended design, RF signal transmission can be delayed by milliseconds, with cascading consequences across the signal chain when signals are not synchronized.

High-frequency signal integrity depends on strict impedance control within the narrow geometries of the PCB trace--impedance is affected by the line's cross-section dimension, shape, line/space width, and dielectric material. The trapezoidal-shaped cross sections common to traces formed using conventional subtractive etching processes can introduce myriad impedance anomalies. The evolution of modified semi-additive processes (mSAP) has helped neutralize this issue, enabling traces to be formed with greater precision, yielding a line with straighter walls that allows for more predictable impedance control.

Whether using mSAP or conventional methods, automated...

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Gale Document Number: GALE|A546960110