How to Select the Right Materials and Processes for Telecom PCBs？

Having worked in hardware design for years, I’ve noticed an interesting phenomenon: whenever telecom equipment PCB design comes up, the first word that pops into people’s minds is “high-speed.” It’s as if boosting data rates will magically solve every problem. In reality, this is a major misconception. True, data rate requirements—from core networks to access points—are becoming staggering, with discussions now extending to 112G and even 224G interfaces. However, I believe the fundamental principle that matters more than “speed” is “stability.” Making a PCB run fast isn’t difficult; the real challenge lies in ensuring it operates consistently and reliably for five or ten years without failure, even in complex environments.

I have seen far too many projects where the pursuit of performance metrics led to the neglect of basic reliability. For instance, we once evaluated a backplane design for a metro aggregation switch. Samples from Supplier A performed flawlessly in standard room-temperature lab tests, outperforming Supplier B across all high-speed signal metrics. Yet, our team insisted on conducting additional tests, including long-term high-temperature/high-humidity aging and thermal cycling. The result? After several hundred cycles, Supplier A’s boards developed microscopic cracks—invisible to the naked eye—in the inner layers, ultimately degrading power integrity. In contrast, Supplier B’s boards, despite slightly inferior initial performance, demonstrated far superior stability. That experience drove home a crucial lesson: stability is the lifeblood of telecom PCBs. Achieving this kind of stability is by no means a simple matter of selecting a so-called “high-end” board material. The market is flooded with terms for various low-loss materials—PTFE, modified epoxy resins, hydrocarbon ceramics—that all sound impressive. However, material selection must be deeply aligned with your specific application scenario. The definition of “stability” differs vastly between a main control board operating in the climate-controlled environment of a core network equipment room and an RF board in an outdoor base station AAU exposed to sun, rain, and drastic temperature fluctuations. For the former, the focus might be on controlling long-term electrical performance drift; for the latter, priorities must shift to mechanical strength, corrosion resistance, and matching coefficients of thermal expansion.

On a deeper level, “stability” is also reflected in the consistency of the manufacturing process. For a complex PCB with dozens of layers, reliability is determined half by design and half by manufacturing. This is especially critical for ultra-thick backplanes (exceeding 5mm) or large packaging substrates (such as those used beneath high-end switching chips). Fluctuations in any detail—be it stress control during lamination, the uniformity of copper plating in vias, or layer-to-layer alignment precision—can become a “ticking time bomb” for future network operations. Procurement decisions often prioritize explicit costs like unit price and lead time while overlooking the hidden costs associated with maintenance and failure rates. The true value of a genuinely “stable” PCB lies precisely in its ability to drastically reduce these latent risks.

My perspective is that we should look at the issue from a different angle: rather than blindly chasing cutting-edge signal speeds and flashy materials, we should focus our energy on building robust, reliable systems engineering capabilities. This entails a thorough understanding of the application environment (is it in a data center rack or on a remote tower?), collaborative design with PCB manufacturers—focusing on Design for Manufacturability (DFM) and Design for Reliability (DFR)—right from the initial design phase, and the establishment of a rigorous verification system that goes beyond standard benchmarks to vet suppliers.

After all, we are building infrastructure for communication networks. Unlike consumer electronics, which can simply be replaced after a couple of years without consequence, a deployed base station or core network switch carries immense responsibility. Its heart—those core network or switch motherboards housing critical chips and high-density interconnects—must be absolutely reliable! This trust isn’t built on flashy spec sheets, but rather on a meticulous process of obsessing over and refining every single detail.

I recently chatted with some friends in the telecommunications equipment industry and noticed an interesting trend: the mere mention of Telecom PCB design and manufacturing gives everyone a headache these days. It feels as though the technical bar has been raised drastically overnight. In the past, simply routing the traces and ensuring signal transmission was often considered “good enough.” But now? The industry’s demands have become almost suffocating.

Take backplanes, for example. We used to view them merely as carriers for connectors; now, they are the most vulnerable yet critical link in the entire system. Signals must travel long distances across them—sometimes exceeding a meter—and the slightest deviation during this journey can cause the entire link to fail. I once saw a project where a mismatch of just a few millimeters in the length of a differential pair caused the eye diagram to close completely; the debugging team spent two full weeks tracking down the root cause. It made me realize that modern design can no longer rely on intuition; it must be driven by data.

Many people believe that using high-end materials solves everything, but I’m not so sure. Materials are certainly important—ultra-low-loss laminates, for instance, do help maintain signal integrity over long distances—but if you fail to address impedance continuity or manage via effects during the design phase, even the best materials won’t save you. I once encountered a board made with top-tier M7 material where the designer failed to properly handle the reference plane at the layer transition; the resulting signal reflection was so severe that the board couldn’t even pass the bit error rate (BER) test.

The shift is even more pronounced in the 5G sector. PCB requirements for base station equipment have diverged sharply: the AAU (Active Antenna Unit) demands high-frequency performance for stable operation in the millimeter-wave band, while the BBU (Baseband Unit) requires ultra-high-density routing, packing thousands of connections into a palm-sized space. These are two completely different design philosophies that must nonetheless work in harmony within the same system.

Sometimes I wonder: are we overcomplicating things? While technical requirements are certainly objective realities, shouldn’t we also reflect on our design methodologies? I see many teams still using workflows from a decade ago to tackle today’s challenges—an approach that clearly no longer suffices.

Take, for instance, the fact that many design software tools now support 3D electromagnetic field simulation, yet few teams actually utilize them. People habitually rely on 2D rule checks, expecting the PCB manufacturer to resolve any remaining issues. In reality, however, once signal rates hit 112G or higher, those 2D rules become obsolete; you must account for electromagnetic field distribution across the entire 3D space to ensure signal integrity.

Another often overlooked aspect is the critical importance of testing and verification. Many teams assume the job is done once the design is sent for fabrication, but modern communication PCBs require rigorous physical testing to confirm performance compliance. This goes beyond simple continuity checks, involving a full suite of high-frequency measurement tools such as Time-Domain Reflectometers (TDR) and Vector Network Analyzers (VNA).

An engineer I know shared an experience regarding a 5G fronthaul network board: despite excellent simulation results, actual measurements revealed excessive jitter. The culprit turned out to be a flawed Power Distribution Network (PDN) design, where simultaneous switching noise was interfering with sensitive signal lines—a problem difficult to detect during simulation and one that only physical testing could expose.

Consequently, I believe communication PCB design has entered a new era; it is no longer merely a matter of layout and routing, but a systems engineering discipline encompassing electromagnetics, thermodynamics, mechanical structure, and even manufacturing processes. A lapse in any single area can lead to total failure.

This places higher demands on us as professionals: we cannot simply be skilled at drafting; we must understand material properties, signal integrity theory, and manufacturing constraints—and even have a grasp of cost control, as clients won’t pay for unlimited performance gains.

I have recently been exploring ways to reduce board material costs without compromising performance—such as using standard FR4 in areas less sensitive to signal loss while reserving ultra-low-loss materials for critical paths. This hybrid strategy has proven viable in real-world projects, effectively balancing cost control with performance requirements. I recently noticed an interesting phenomenon while chatting with friends in the telecommunications equipment sector. Whenever the conversation turns to PCBs for the communications industry, people tend to focus on high-end technical specifications and market data. Yet, I feel that behind these numbers, a fundamental aspect is often overlooked: reliability in actual application.

You might wonder how complex a small circuit board could possibly be. However, the situation changes completely when you place it inside a base station running 24/7 or tuck it into the high-temperature, high-density racks found in data centers. I’ve seen many projects that looked impressive on paper—utilizing various advanced manufacturing processes—only to fail in the field. Issues like poor heat dissipation or material degradation in humid environments forced entire batches of boards to be reworked. For instance, in coastal or industrial areas, salt spray and corrosive gases accelerate the aging of solder joints and conductive traces; if specific protective coatings and materials aren’t selected during the design phase, hidden risks are created.

Many companies are currently chasing cutting-edge 5G technology. While that is certainly valid, sometimes it feels like putting the cart before the horse. In the pursuit of specific performance metrics, boards are designed with increasing complexity, higher layer counts, and finer trace widths. While this does boost performance, it also causes manufacturing difficulties and maintenance costs to skyrocket. Ultra-fine traces, for example, demand extremely high precision in etching and substrate uniformity; even a tiny defect can lead to catastrophic signal integrity issues. Meanwhile, poor lamination in multi-layer boards can cause faults like inner-layer delamination, which are notoriously difficult to detect.

An engineer I know once managed an overseas project where they procured a batch of “high-performance” communication boards for a local network upgrade. Due to the hot climate and unstable power supply, the failure rate turned out to be far higher than expected. Ultimately, while the initial purchase price per board seemed reasonable, the total investment—factoring in subsequent maintenance costs and losses from downtime—ended up being much higher. This highlighted a lack of validation regarding regional adaptability; the products hadn’t undergone stress testing during R&D to simulate the extreme environmental conditions of the target market.

This reminds me of another example. To cut costs, some manufacturers compromise on materials by choosing lower-specification substrates. Problems might not be apparent in the short term, but over long periods of operation, signal attenuation becomes significant—especially in high-frequency applications. These hidden costs are often completely overlooked at the outset. In frequency bands like millimeter-wave, the stability of a substrate’s dielectric constant (Dk) and dissipation factor (Df) is critical; inexpensive materials are highly susceptible to temperature and humidity fluctuations, which directly causes signal quality to vary over time and across environments.

The entire industry is currently buzzing about the opportunities presented by AI and big data, which have indeed driven demand for high-end PCBs—particularly those used in servers and data centers. However, I believe we shouldn’t simply chase the accumulation of technical specifications; instead, we should focus on balancing performance, reliability, and cost. For instance, while AI accelerator cards require ultra-high-density interconnects, blindly pursuing the fastest materials could double the board’s cost. Conversely, optimizing the layout and using mid-to-high-speed materials with a better price-performance ratio can often significantly enhance reliability and manufacturability while still meeting performance requirements.

Sometimes, the simplest solution is the most effective. In certain scenarios, for example, slightly lowering unnecessary performance targets and opting for more mature manufacturing processes can actually lead to a more stable system with a longer lifespan. After all, for network operators, stable network operation matters more than raw performance metrics. Take edge access devices: using a field-proven 6-layer or 8-layer board design often yields far better results in terms of production yield and long-term failure rates compared to a 12-layer board forced into existence just to meet a specific benchmark.

I am not opposed to technological progress—on the contrary, I believe innovation is vital. I simply think we need to be more pragmatic and focus on real-world applications rather than being led around by flashy numbers. R&D should begin with an analysis of application needs, not just a comparison of specifications.

Ultimately, whether it involves traditional telecom equipment, emerging 5G applications, or the rapidly growing data center sector, the PCB serves as a fundamental component; its quality directly impacts the entire system’s performance. We must prioritize this, but without getting caught up in a blind race for technical specs. An excellent PCB design is the result of multidisciplinary optimization—balancing electrical performance, thermal management, mechanical strength, environmental resilience, and manufacturability.

I believe the industry will gradually return to a more rational approach in the coming years, with a greater focus on overall product value rather than just isolated metrics. After all, end-users want a stable, reliable system capable of long-term operation, not just a stack of impressive data reports. This means that a quality control system covering the entire lifecycle—from design and material selection to manufacturing and testing—will become far more important than chasing the peak of any single technical parameter.

Many people tend to think that a telecom PCB is “just a circuit board,” after all. But I have to say, that’s an overly simplistic view. The boards we produce aren’t just run-of-the-mill components! They have to withstand all sorts of extreme environments—just picture equipment mounted atop a tower! They get scorched by the summer sun and frozen solid in winter, yet they must keep operating reliably. There’s a lot of technical nuance involved here. For instance, materials must undergo rigorous selection to ensure their coefficient of thermal expansion matches that of the copper foil across a drastic temperature range of -40°C to 85°C; otherwise, the lamination could crack, leading to open circuits.

When it comes to signal transmission, people might think it’s just a matter of letting the current flow through! But the real challenge lies in ensuring the signal reaches its destination clean and intact. This is especially critical with high-speed data; even the slightest deviation in trace design can cause system-wide failures! I’ve seen plenty of cases where poor impedance control led to intermittent disconnections or maddeningly slow speeds—problems that can’t simply be fixed by swapping out a single part! For example, in high-speed serial links exceeding 25Gbps, even micrometer-level errors in microstrip width or dielectric thickness can trigger severe signal reflection and loss, necessitating precise modeling and optimization via simulation software.

In reality, I think many people place too much blind faith in new materials, always looking to the latest and most expensive substrates to solve problems. However, the actual situation is often far more complex. Sometimes, the issue lies in fundamental aspects like trace layout—such as two critical signal lines being too close and interfering with each other, or a flawed power supply design causing instability that degrades signal quality. It is in these details that an engineer’s true expertise is tested. A classic example is the need to maintain a spacing of at least three times the trace width between differential pairs to minimize crosstalk, while also avoiding the routing of fast-switching digital clock lines near sensitive signal paths.