When we open a smartphone, laptop, or fiddle with a smart watch or router, we instinctively think that the core PCB (printed circuit board) of these precision electronic devices must surely be “multilayer” — after all, with modern electronics shrinking and becoming more powerful, how could a single-layer copper foil support the dense components and complex signal transmission?
However, the truth is far more nuanced: not all modern electronic devices rely on multilayer PCBs. Single- and double-sided boards are still widely used in numerous applications, and the choice of PCB layers has never been about “the more, the better” — it’s about a precise balance between functionality, cost, size, and reliability.
In this article, we’ll dive deeper into this topic, analyzing the application boundaries of different-layer PCBs, exploring which devices absolutely require multilayer boards, which still depend on single/double-sided boards, and what the key considerations are for engineers when selecting the appropriate type.
Single-Sided vs. Double-Sided vs. Multilayer
Single-Sided PCB
Single-sided boards are the simplest PCBs, with copper foil applied only to one side of the insulating substrate. All electronic components are soldered to this side, and the traces are laid on the same layer. Because traces can only be routed on a single plane, the layout is highly constrained, and complex circuit connections are not possible. Additionally, they have poor anti-interference capability and are almost incapable of handling high-speed signals.
However, their key advantage lies in simplicity: they are the least expensive, easiest to manufacture, and most efficient for mass production. There is no need for complex lamination or vias, making them ideal for extremely simple circuits. While single-sided boards are “low-end,” they have never been eliminated and remain the top choice for many low-cost devices.
Double-Sided Board
In a double-sided board, copper foil is applied to both sides of the insulating substrate. Through-hole vias (metal holes that penetrate the substrate) allow traces to connect between the two sides, enabling more flexibility in component placement and routing.
Compared to single-sided boards, double-sided boards can accommodate more complex circuits, reduce trace crossings, and are suitable for medium-sized electronic devices. They are easier to produce and cost-controlled compared to multilayer boards, offering an optimal solution between “low cost” and “moderate complexity.” Today, double-sided boards still hold a significant market share, especially for consumer electronic devices.
Multilayer Board
In the industry, PCBs with 4 layers or more are typically classified as multilayer boards. These are constructed by alternating copper foil layers between multiple insulating substrates and laminating them under high temperature and pressure. The copper layers in the middle can serve as power layers, ground layers, or signal inner layers, with blind and buried vias (rather than through-hole vias) enabling interlayer connections, greatly saving internal space.
The main advantage of multilayer boards is “high performance”: a dedicated power layer and ground layer effectively reduce signal interference and optimize impedance control, making them suitable for high-speed and high-frequency signal transmission. Additionally, the multilayer layout allows for more components and traces in a limited space, supporting the demand for miniaturization and high-density integration of devices. The more layers, the higher the integration and anti-interference capabilities, but the complexity, material costs, and yield control challenges also increase exponentially.
Common multilayer boards have 4, 6, and 8 layers. For high-end devices like foldable smartphones, AI servers, and aerospace equipment, the number of layers can reach 16, 30, or even more than 70 layers, posing a great challenge to the equipment and technical capabilities of PCB manufacturers.
Which Devices Absolutely Require Multilayer PCB?
The high cost and complexity of multilayer PCBs mean they are not used indiscriminately. They are required only in devices with strict performance, integration, and anti-interference requirements, where single- or double-sided boards simply cannot meet the needs and would cause the device to malfunction.
High-End Consumer Electronics
Devices such as smartphones, tablets, laptops, and high-end cameras are core applications for multilayer PCBs. Take smartphones as an example: today’s flagship phones have mainboards smaller than the size of a palm, yet they need to integrate processors, memory, camera modules, 5G RF chips, battery management chips, and hundreds of other components, along with handling high-speed signals like DDR and PCIe. Single- and double-sided boards cannot accommodate such high-density routing.
Currently, most smartphones use 6–12 layers for the mainboard, while foldable phones, which have more complex structures and need to balance flexibility and performance, can have over 16 layers. High-end laptops typically have mainboards with 8–16 layers, and gaming laptops and workstations, due to their high-performance GPUs and processors, can have even more layers. High-end cameras also require multilayer boards to ensure the integrity of image signal transmission and avoid interference that could degrade image quality.
The primary requirement for these devices is “miniaturization + high performance,” and multilayer boards, particularly 2+N+2 HDI PCB, are the only solution — using blind and buried vias, fine-line processes to connect thousands of solder joints in a very small space while ensuring stable high-speed signal transmission.
High-Speed Digital and Communication Devices
Devices such as routers, switches, servers, and 5G base stations require extremely high-speed signal transmission, making multilayer boards essential to maintaining signal integrity. These devices process large amounts of high-frequency, high-speed data, and any signal interference can result in packet loss, increased latency, and decreased stability. Multilayer boards, with their dedicated power and ground layers, form “shielding chambers” that effectively suppress electromagnetic interference (EMI), optimize impedance matching, and reduce signal reflection.
Standard home routers typically use 4–8 layers for their mainboards, while enterprise-grade switches and routers may use 8–20 layers. High-end servers and switches with multiple GPUs and CPUs may use 20–40 layers, and some devices’ backplanes (core circuit boards connecting modules) can exceed 70 layers — setting a new standard for PCB layer counts.
5G base stations, with core modules like the RRU (Remote Radio Unit) and BBU (Baseband Unit), require 10–20 layers of multilayer boards to meet the high-frequency signal transmission needs of 5G while withstanding the complex electromagnetic environment outdoors, ensuring stable communication.
Automotive and Industrial Electronics
With the advancement of automotive electronics in terms of intelligence and electrification, the complexity of automotive electronics has greatly increased, and the reliability requirements for PCBs have surpassed those of consumer electronics. Vehicles face high and low temperatures, vibration, electromagnetic interference, and other harsh environments. Since these devices relate to driving safety, there is zero tolerance for failure, and multilayer boards have become the mainstream choice for automotive PCBs.
Core modules like ECU (Electronic Control Units), ADAS (Advanced Driver Assistance Systems), and BMS (Battery Management Systems) typically use 4–10 layers of multilayer boards, which can support complex control circuits and use ground layers to separate analog and digital signals to avoid interference. Industrial controllers, inverters, and other equipment in harsh working environments also commonly use 4–8 layers, balancing reliability and anti-interference capabilities.
Medical and Aerospace
Medical equipment (such as medical imaging devices, ECG monitors, and in vitro diagnostic devices) and aerospace equipment (such as satellites, drones, and avionics systems) have the most stringent requirements for PCBs. These devices need to meet high performance and anti-interference standards, with extremely high reliability and stability. In some cases, lightweight and radiation resistance are also required, making multilayer boards the only viable option.
Medical imaging devices (such as CT and MRI) need to process high-precision image signals, with PCBs often ranging from 10 to 30 layers to ensure lossless signal transmission. Satellite and avionics equipment need to withstand space radiation and extreme temperatures, with PCBs reaching 20 to 40 layers, made with special materials and processes for long-term stable operation. Drone flight control modules also require multilayer boards to achieve precise control while balancing light weight and reliability.
Which Devices Are Still Using Single/Double-Sided PCBs?
After reviewing the application scenarios for multilayer boards, many may assume that single- and double-sided boards have become ‘outdated.’ However, in fact, single- and double-sided boards still dominate a vast array of low-complexity, low-cost applications due to their extremely low cost and simple manufacturing process. For these devices, ‘just enough’ is far more important than ‘ultimate performance,’ making the optimization of PCB cost a key consideration.
Ordinary Household Appliances
Many common household appliances, which have simple functions and circuits, don’t require multilayer boards. Single- and double-sided boards are sufficient for these needs, and cost control is critical for these products.
For example, remote controls (for TVs, air conditioners, set-top boxes) primarily transmit infrared signals and have only simple components like buttons, chips, and infrared emitters. A single-sided board is enough for the wiring, keeping costs extremely low. Small appliances like table lamps, fans, electric kettles, and basic power outlets mainly focus on power control and switches with simple circuits. A double-sided board is more than adequate, and it can reduce costs by 30%–60% compared to a four-layer board, which is crucial for mass production of small appliances.
Even some auxiliary modules of mid-range home appliances (such as lighting modules in refrigerators or indicator light modules in washing machines) still rely on single- or double-sided boards, as there’s no need to pay for unnecessary performance.
Basic IoT and Sensors
The development of IoT (Internet of Things) has led to a wide range of low-cost, low-complexity sensors and simple smart devices, where the core requirement is “simple data transmission.” These devices don’t need to handle high-speed signals, and double-sided boards are sufficient to meet their needs.
For instance, temperature and humidity sensors, door/window sensors, infrared relays, and basic smart plugs typically have few I/O interfaces and don’t require high-speed signal transmission. The circuit structure is simple, and a double-sided board can handle the routing and keep costs low, making it the main choice for these products. Low-end Bluetooth modules (like BLE low-power Bluetooth) that are simple and don’t need to interconnect multiple devices also use double-sided boards to keep the price point competitive.
For these basic IoT devices, the market is highly competitive, and price sensitivity is high. Using single- or double-sided boards can significantly improve product cost-effectiveness, capturing a larger share of the mid-to-low-end market.
Toys and Consumer Small Electronics
Children’s toys (such as remote-controlled cars, electric building blocks, and toy robots) and consumer small electronics (such as LED strips, basic chargers, earphone charging cases, and mini speakers) have very low performance requirements. Their primary focus is “low cost and reliable operation,” and single- or double-sided boards are the optimal choice.
Take LED strips as an example: the circuit only needs to power the LEDs and turn them on, and a single-sided board can accomplish the wiring, significantly lowering production costs. Simple chargers focus on power conversion, with straightforward circuits, and double-sided boards are more than enough, without needing to go for multilayer designs. For children’s toys with single-function electronics, cost control is key, and single-sided boards remain the mainstream choice, with low replacement costs in case of malfunction.
General Power Supplies and Adapters
General switch-mode power supplies (SMPS), phone chargers (excluding high-end gallium nitride models), and printer power supplies focus primarily on power conversion, with simple signal transmission and no high-speed or high-frequency requirements. Double-sided boards are fully sufficient for these devices.
The core requirement for these devices is stable power supply, not high performance. Double-sided boards can provide the necessary layout and wiring for power components while keeping costs under control. Only high-end gallium nitride chargers, which have higher power density and require heat dissipation and signal interference optimization, use four-layer boards, while regular chargers don’t need multilayer boards.
It’s Not About “More Layers,” But “Fit”
From the analysis above, it’s clear that the PCB selection for modern electronic devices is essentially a balancing act. Engineers don’t blindly pursue higher layers, nor do they opt for overly simplistic designs to save costs. The core consideration is finding the optimal solution based on four key factors: performance, cost, size, and reliability.
Routing Density: “Fit the Space” is the Foundation
Routing density is the primary consideration: if a device has few components, minimal pins, and simple wiring, single- or double-sided boards can easily accommodate all the traces, and there’s no need for multilayer boards. However, if the device has a dense component layout, like flagship mobile processors with thousands of pins, single- or double-sided boards can’t prevent trace crossings and won’t fit all the routing, necessitating a move to multilayer boards, which allow routing on inner layers.
For example, the processor in a smartphone has far more pins than a double-sided board can handle, requiring multilayer boards with inner-layer traces and blind/buried vias to connect all the pins. On the other hand, a remote control chip has just a few pins, and a single-sided board can easily handle the routing.
Signal Integrity: The “Hard Constraint” for High-Speed Signals
For devices that need to process high-speed, high-frequency signals (such as DDR memory, 5G RF, or PCIe data signals), signal integrity becomes the core constraint. These signals are highly sensitive to interference, impedance matching, and signal reflection. Single- or double-sided boards can’t provide a full power layer and ground layer to suppress interference, leading to signal distortion and data loss.
Multilayer boards, with separate power and ground layers, provide stable reference planes for high-speed signals, reducing interference, optimizing impedance control, and ensuring signal integrity. Low-speed signals, such as infrared signals in remote controls or analog signals in sensors, are less sensitive to interference, and single- or double-sided boards suffice.
EMC/EMI: The “Baseline” for Anti-Interference Ability
Electromagnetic compatibility (EMC) is a mandatory requirement for electronic devices, ensuring they don’t interfere with other devices and can withstand external electromagnetic disturbances to function properly. For circuits that are highly sensitive to or generate strong interference (such as circuits mixing analog and digital signals or high-frequency circuits), multilayer boards’ ground layers provide isolation, reducing interference between circuits and improving EMC performance.
For example, automotive electronics must resist electromagnetic interference from car engines, radars, and other systems, and multilayer boards are essential for ensuring EMC performance. In contrast, the circuit in a simple table lamp produces minimal interference and doesn’t need complex anti-interference measures, so a single-sided board is sufficient.
Cost and Mass Production: The “Core Consideration” for Commercialization
No matter how high the performance requirements, the cost are an unavoidable factor in commercialized products. With each additional layer in a PCB, material costs, process costs, and yield control costs increase significantly: a four-layer board costs 30%–50% more than a double-sided board, an eight-layer board costs 50%–80% more than a four-layer board, and for PCBs with 20 or more layers, costs increase exponentially, and yield control becomes much harder.
Thus, for low-cost, mass-produced products (such as small appliances and toys), single- or double-sided boards are preferred to minimize costs. For high-end products (such as flagship smartphones and AI servers), performance is the core competitive advantage, and manufacturers are willing to bear the higher cost of multilayer boards. For products in between, (such as mid-range IoT devices), four-layer boards strike a balance between performance and cost.
2026 PCB Industry Landscape
High-End and Complex Devices
Multilayer boards dominate and will continue to increase in layer count. AI computing power has driven the demand for high-layer PCBs, automotive intelligence has fueled the growth of automotive multilayer boards, and aerospace and medical devices will steadily demand high-layer, highly reliable PCBs. This field is the core market for multilayer boards and a key focus of technological competition for PCB manufacturers.
Mid- and Low-End Devices with Simple Functions
Single- and double-sided boards will remain dominant. Small appliances, toys, basic IoT devices, and standard power supplies have a huge market demand and are highly price-sensitive. Single- and double-sided boards will continue to hold a large share of this market, becoming the “basic foundation” of the PCB industry.
Middle Ground
Four-layer boards become the “sweet spot.” Many mid-range IoT devices, entry-level consumer electronics, and basic automotive modules need a certain level of performance and integration while controlling costs. Four-layer boards offer the best balance, addressing issues like routing density and anti-interference while avoiding the high costs of high-layer PCBs. This is the largest market segment for PCB shipments today.
Conclusion
Returning to the original question: Are all modern electronic devices using multilayer PCBs? The answer is clearly no.
The number of PCB layers is never a measure of a device’s ‘level’ but rather a rational choice made by engineers based on device functionality, signal requirements, cost considerations, and manufacturing constraints. Engineers have mastered a variety of technologies to select the most suitable PCB structure for a device’s needs, ensuring the highest efficiency and reliability at the lowest cost. For high-end devices requiring multilayer PCBs, the expertise of specialized multilayer PCB manufacturers becomes crucial to meet the demands of advanced performance, complexity, and reliability.
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