As the electrification of commercial vehicles and construction machinery accelerates, WAIN delivers a cutting-edge solution: our integrated metal-shell connectors designed specifically for high-voltage power distribution units (PDUs). Engineered for demanding environments, this series combines robust performance with installation efficiency.

Exceptional Load Capacity – Precision-engineered design supporting 1–4 core configurations, with a maximum voltage rating of 2000 V and current up to 450 A.

Comprehensive Protection – Certified IP67/IP6K9K sealing with 360° shielding to safeguard against harsh environmental conditions and electromagnetic interference.

Versatile Installation – Multiple keying options and straight or angled cable outlets ensure optimal compatibility and significantly reduce installation time.

Proven in the field, these connectors are already in bulk supply to multiple Tier 2 high-voltage component manufacturers, delivering stable performance and reliable integration. Today, they are enabling mass-production applications across a wide range of commercial vehicles and construction machinery, helping power the next generation of new energy transportation. 

Crystal oscillators are widely used in the Internet of Things (IoT) and play a key role. The following is a detailed introduction to some specific applications of crystal oscillators in the IoT:

1. Provide accurate clock signal

A crystal oscillator generates the clock frequency signal necessary for the CPU to execute instructions. All instructions are executed based on this signal. Furthermore, by providing a precise clock signal, a crystal oscillator facilitates synchronous data transmission, preventing data loss or misalignment. For example, a 32.768 kHz crystal oscillator is a common clock source in IoT devices. It provides a stable clock signal, ensuring proper operation.

PSX315 3.2*1.5*0.9mm  32.768KHz Crystal

2. Data collection and time synchronization

1） Data collection

In IoT devices, crystal oscillators provide an accurate clock reference, helping to achieve timed data acquisition and ensuring the accuracy and reliability of data sampling. This is crucial for IoT systems to obtain accurate data information.

2）Time synchronization

Crystal oscillators provide accurate clock signals that can be used to trigger events and synchronize time between devices. Multiple devices in an IoT system must work together, and crystal oscillators provide a unified time base to ensure consistent operation across all devices. This is crucial for achieving overall system synchronization and collaboration.

3.Low power design

IoT devices often need to operate for extended periods, making low-power design crucial. Certain crystal oscillators, such as 32.768kHz, can operate low-power devices for extended periods in power-saving mode, helping to extend the battery life of IoT devices. This is crucial for the practical application and widespread adoption of IoT devices.

DTLF206 2*6mm 32.768khz cylindrical crystal with low power consumption

4.Miniaturization and integration

As IoT devices become increasingly miniaturized and integrated, crystal oscillator products are also evolving towards smaller, lower-power designs. Miniaturized crystal oscillators better meet the size and weight requirements of IoT devices, enhancing their portability and flexibility. Furthermore, integrated crystal oscillators help simplify device circuit design and production processes, reducing costs and improving production efficiency.

5. Diverse application scenarios

IoT systems encompass a wide range of applications, including smart homes, smart cities, and industrial control. Different applications have varying requirements for crystal oscillators, such as frequency stability, power consumption, and size. Therefore, IoT systems must select crystal oscillator products tailored to their specific needs. For example, in the smart home sector, temperature-compensated crystal oscillators (TCXOs) are widely used due to their high precision and stability. However, in industrial control, crystal oscillators with enhanced shock and interference resistance may be required.

PTC1612  1.6 * 1.2 * 0.59 mm   TCXO quartz crystal oscillator

6. High precision and time-frequency technology

IoT applications sometimes require high-precision clock signals and time-frequency technologies. As a core component of the frequency source, the performance of the crystal oscillator directly impacts the system's clock accuracy and stability. Therefore, high-performance crystal oscillator products are essential for high-precision IoT applications. For example, GPS positioning and network transmission modules require high-precision crystal oscillators to ensure communication synchronization and positioning accuracy.

In summary, crystal oscillators play an irreplaceable role in the Internet of Things (IoT). With the continuous development of IoT technology, the application of crystal oscillators will become more extensive and in-depth. Furthermore, with the continuous advancement and innovation of crystal oscillator technology, more high-performance, low-power, and miniaturized crystal oscillator products will be applied to the IoT in the future, providing better support for the development of IoT technology.

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In the realm of high-speed digital circuit design and system integration, the crystal oscillator acts as the system's "heartbeat." The quality of its output signal is paramount, directly determining the overall system's stability and performance. However, navigating the myriad of output types listed in datasheets—CMOS, LVDS, LVPECL, HCSL, and Clipped Sine—can be a common source of confusion for engineers. This article provides an in-depth comparison of these five primary oscillator output types, empowering you to make the perfect choice for your next project and ensure an optimized, highly reliable system design.

Understanding Output Logic: From General-Purpose to Specialized Solutions

Fundamentally, we can categorize these outputs into two main families: single-ended and differential CMOS/LVCMOS output oscillators and Clipped Sine wave oscillators fall under single-ended signals. They feature simple circuit structures and are the ideal choice for low-power clock oscillators and general-purpose microcontroller clock sources, dominating in cost-sensitive consumer electronics where frequencies are not extremely high. However, single-ended signals are susceptible to noise and show their limitations in high-speed, long-distance transmission. This is where differential signaling technology shines. LVDS differential oscillators, LVPECL clock oscillators, and HCSL output clocks all utilize a pair of opposite-phase signals for transmission, offering superior common-mode noise rejection, lower electromagnetic radiation (EMI), and excellent low jitter characteristics. They are the definitive solution for challenging EMI environments and enhanced signal integrity.

The Differential Face-Off: Application Territories of LVDS, LVPECL, and HCSL

Although all are differential outputs, LVDS, LVPECL, and HCSL each have their own distinct design and application strengths. LVDS crystal oscillators are known for their very low power consumption and moderate speed, making them the preferred choice for FPGA high-speed interface clocks, flat-panel display drivers, and clocks for high-speed data converters. They provide a stable, low-jitter reference clock while effectively controlling overall system power. LVPECL oscillators, on the other hand, represent the peak of performance, offering the fastest switching speeds and best jitter performance, but at the cost of higher power consumption and more complex termination networks. They are typically used in areas with extremely stringent timing requirements, such as network communication equipment clocks, optical modules, and base stations. Meanwhile, the HCSL output type is almost exclusively the standard configuration for PCIe clock generators. Its specific current-steering structure provides the PCI Express bus with a clock signal featuring sharp edges and ultra-low jitter, making it an indispensable clock component in hardware like motherboards, graphics cards, and solid-state drives (SSDs).

The Elegant Solution for Specialized Scenarios: Clipped Sine Wave

Among the plethora of square wave outputs, the Clipped Sine wave oscillator is a unique presence. It outputs a shaped sinusoidal wave whose harmonic content is significantly lower than that of a square wave, thereby substantially reducing electromagnetic interference. This low EMI crystal oscillator is primarily used in RF circuit clocks and as a local oscillator (LO) source for microwave systems, providing a "clean" clock signal to sensitive analog circuits and preventing digital noise from contaminating high-frequency analog signals.

Precise Selection Guide: Matching the Perfect "Heartbeat" to Your Project

Selecting the right crystal oscillator is a critical step for project success. If your design is for an industrial control mainboard or an IoT device core board with strict cost and power constraints, then a CMOS/LVCMOS output oscillator in a 3225 package crystal or a 2520 chip oscillator will be an economical choice. If you are designing a high-speed serial communication card or working on server clock distribution circuits, LVDS is the most versatile differential option due to its balanced performance. For designs that must comply with PCIe Gen 3/4/5 clock specifications, you must select an oscillator with an HCSL output. And for any application involving a high-frequency RF sampling clock, Clipped Sine output should be prioritized to ensure minimal system noise.

In conclusion, no single output type is a universal solution. Understanding the universality of CMOS, the balance of LVDS, the high performance of LVPECL, the specialization of HCSL, and the low noise of Clipped Sine is fundamental to making the best technical decision. As a professional crystal oscillator supplier, we offer a full range of high-stability active crystal oscillators and programmable oscillators to help you effortlessly meet a wide array of demanding design challenges.

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Recent discussions surrounding the security of time service centers have brought a critical technology into focus: frequency and timing technology. At the Frequency and Time Benchmark Laboratory in Xi'an, every tick of "Beijing Time" is vital to the operation of critical infrastructure sectors  such as the BeiDou Navigation Satellite System, financial transactions, and power grid management. Supporting this system are tiny components no larger than a fingernail:crystal oscillators.

Crystal Oscillators: The Heartbeat of Precision Timing

While the cesium and hydrogen atomic clock ensembles at the National Time Service Center (NTSC) form the primary time reference, it is crystal oscillators that enable the reliable distribution of UTC (NTSC) signals across the country:

VCXOs (Voltage Controlled Crystal Oscillators) serve as relay stations for long distance time transfer. Using the satellite common view technique, they regenerate synchronized signals over thousands of kilometers with sub nanosecond precision.

OCXOs (Oven Controlled Crystal Oscillators) provide the stability required by critical infrastructure. In applications such as timing monitoring stations, properly calibrated OCXOs reduce timing discrepancies to nanosecond levels, meeting the stringent synchronization requirements of 5G networks and radar systems.

Exceptional Cost Efficiency: Compared to high cost atomic clocks, crystal oscillators deliver high timing accuracy at a fraction of the cost, making them the preferred solution for BeiDou terminals and financial servers.

                          VCXO3225

The Critical Role of Crystal Oscillators in National Infrastructure  

The stability of crystal oscillators directly impacts multiple vital systems:

Navigation Systems:Satellite ground clock offset measurements rely on oscillators for calibration. Accuracy degradation directly affects positioning precision.

Financial Systems:Modern trading platforms require microsecond level timestamp synchronization. Oscillator anomalies can cause  transaction disorders and market instability.

Power Grid Operations:Nationwide grid coordination depends on unified timing signals. Even minimal oscillator drift may trigger cascading grid failures.

The Unseen Timing Engine in Everyday Life 

Crystal oscillators operate silently in countless applications: every cellular handover, high speed rail system relying on  millisecond level synchronization, and even the precise striking of the New Year bell relies on their accurate "timekeeping."

In an era of technological advancement, these miniature components form the foundation of reliable timing systems. Every nanosecond of precision represents both engineering excellence and operational security

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Equivalent Series Resistance (ESR)  is a critical parameter for evaluating the performance of a  crystal oscillator, directly reflecting the degree of energy loss during its resonant state. Whether for  kHz-range tuning fork crystal units or MHz-range AT-cut crystal units, the ESR value is influenced by a combination of factors. A deep understanding of the relationship between ESR, package size, and operating frequency is essential for optimizing circuit design and component selection.

ESR Characteristics of kHz Crystal Units  

In the kHz frequency range, crystal oscillators typically utilize a tuning fork crystal element. Due to their specific vibration mode, kHz crystals generally exhibit relatively high ESR values. Our product data shows a clear correlation between package size   and ESR for kHz crystal units:

      1.6×1.0mm package  : Maximum ESR of 90 kΩ  

      2.0×1.5mm package  : Maximum ESR of 70 kΩ  

      3.2×1.5mm package  : Maximum ESR of 70 kΩ  

      6.9×1.4mm package  : Maximum ESR of 65 kΩ  

      8.0×3.8mm package  : Maximum ESR of 50 kΩ  

     10.4×4.06mm package  : Maximum ESR of 50 kΩ  

These  ESR characteristics  give kHz crystal oscillators distinct advantages in low-power applications, making them particularly suitable for IoT devices and portable electronics requiring long battery life.

ESR Analysis of MHz Crystal Units  

MHz crystal oscillators  employ an AT-cut thickness-shear vibration mode, and their   ESR characteristics  follow more complex patterns. Based on our technical analysis, the ESR of an MHz crystal unit is influenced by both its package size and its operating frequency.

For a given package size,   ESR typically decreases as the frequency increases. This is primarily because higher-frequency crystals use thinner crystal blanks, resulting in lower vibrating mass and relatively reduced energy loss. However, the specific ESR value must be determined by considering both the specific frequency point and the   package size  .

Our product line covers various  package sizes from  1.6×1.2mm  to 7.0×5.0mm, with each package optimized for specific frequency ranges and ESR requirements.

In-Depth Technical Principle Analysis  

Mechanism of kHz Crystals  :

Tuning fork crystals  have a relatively large vibration amplitude. The package size   directly affects the vibration space of the tuning fork arms and the  air damping effect. A larger package provides a more sufficient vibration environment, reducing mechanical constraints, which helps lower the ESR.

Mechanism of MHz Crystals  :

The ESR characteristics of the AT-cut thickness-shear mode are more complex. Beyond the influence of package size, the operating frequency becomes a key factor determining the ESR value. Due to their thinner crystal blanks and optimized   electrode design, high-frequency crystals generally achieve lower ESR values. This inverse relationship between frequency and ESR is a key characteristic of MHz crystal oscillators  .

Professional Application Selection Guide  

Selection Strategy for kHz Crystals :

Ultra-Low-Power Devices  (e.g., smartwatches, IoT sensors): Prioritize 1.6×1.0mm   or 2.0×1.5mm packages  .

Industrial Control and Automotive Electronics: Recommend 3.2×1.5mm and larger   package sizes  .

High-Precision Timing Modules  : Choose larger package sizes like 8.0×3.8mm for better stability.

Selection Strategy for MHz Crystals  :

It is necessary to understand the  ESR characteristics  at the specific frequency point   in detail.

Comprehensively consider the relationship between package size and operating frequency.

Select the appropriate ESR range based on the power consumption and stability requirements of the application scenario.

Technology Development Trends  

As electronic products evolve toward multi-functionality and miniaturization, crystal oscillator technology continues to innovate. In the kHz domain, we are developing even smaller package technologies  to reduce size further while maintaining low-power characteristics. In the MHz domain, technological development focuses on supporting higher frequencies and better ESR performance within smaller dimensions.

System-in-Package (SiP) technology shows great potential in both frequency ranges. By integrating the oscillation circuit with the crystal resonator, the overall ESR characteristics can be optimized. We are committed to providing more precise   frequency control solutions  through continuous technological innovation.

Conclusion  

The ESR characteristics  of a crystal oscillator result from the combined effects of   package size, operating frequency  , and crystal blank design. For kHz crystals, ESR   is primarily influenced by package size, whereas for MHz crystals, the complex interaction between package size and operating frequency must be considered simultaneously.

A correct understanding of  ESR  helps engineers make more accurate component selection decisions during project development. We recommend carefully evaluating the requirements of the specific application and selecting the most suitable crystal oscillator product based on the operating frequency and package requirements.

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We provide comprehensive technical support to help customers choose the most suitable crystal solution  based on specific application scenarios and performance requirements, ensuring optimal system performance and reliability.

In electronic devices, the tuning fork crystal units serves as a core component for frequency control, and its package type directly influences circuit design and overall performance. The two mainstream packaging forms are through-hole (DIP) and surface-mount (SMD). DIP crystals, such as HC-49S, HC-49U, UM-1, and cylindrical types (e.g., 2×6 mm and 3×8 mm), use pinned leads for insertion into PCB holes. They are generally larger in size and offer high stability, making them suitable for applications like industrial control systems and communication base stations where space is not critical but reliability is essential.

                                                                                               DIP Tuning Fork Crystal Units

In comparison, SMD crystals—including packages such as SMD1612, SMD3225, SMD5032, and SMD-Glass3225—utilize surface-mount technology (SMT) to achieve ultra-miniaturized footprints, with dimensions as small as 1.6×1.2 mm. These components are ideal for high-density electronic products such as smartphones, wearables, and IoT modules.

                                                                                               SMD Tuning Fork Crystal Units

From an assembly perspective, DIP crystals require through-hole insertion and are typically soldered using wave soldering or manual techniques. While not suitable for full automation, they allow easier repair and replacement. On the other hand, SMD crystals are compatible with fully automated pick-and-place and reflow soldering processes, significantly improving production efficiency and reducing costs for high-volume manufacturing.

In terms of mechanical and environmental robustness, the SMD package offers better resistance to vibration and shock due to its firm attachment to the PCB. This makes it a preferred choice for automotive electronics and portable devices demanding high reliability. Although DIP packages are more susceptible to physical stress in dynamic environments due to their longer leads, they remain popular for prototyping and low-volume production due to ease of handling.

                                     SMD Crystal Reel

In summary, selecting between SMD and DIP tuning fork crystal units should be based on package size, production process, operating environment, and cost requirements. SMD crystals are better suited for miniaturized, automated consumer electronics, while DIP crystals are often chosen for high-reliability industrial and special-purpose applications. As a professional crystal oscillator manufacturer, we supply a comprehensive range of DIP and SMD tuning fork crystals and can help recommend the optimal frequency control solution for your needs.

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During the debugging of Gigabit Ethernet equipment or high-end audio interfaces, engineers often encounter a precise challenge: an HC-49/U quartz crystal, nominally rated at 25.000MHz or 24.576MHz, shows a tiny frequency deviation, causing equipment to desynchronize or impairing audio quality. A cost-effective and common solution is placing a small spacer under the crystal's metal shell. This is not just a mechanical fix but a precise frequency-tuning process. So, what is the core purpose of adding a spacer to an HC-49/U crystal, and which frequencies most commonly require it?

           HC-49/U Crystal with Spacer

Core Function  1: Precision Frequency Trimming for Strict Standards  

The primary role of a spacer is  precision frequency micro-adjustment. The frequency of an HC-49/U crystal is highly sensitive to changes in its load capacitance. Adding an insulating spacer increases the distance between the quartz wafer and the metal base, thereby reducing the equivalent parallel capacitance. For a fundamental-mode crystal, this causes its resonant frequency to increase slightly(and vice-versa). By selecting spacers of different thicknesses, fine calibration at the ppm level is achievable.

This is critical in high-speed communication and high-precision audio applications.

For instance:

• 25.000MHz is standard for Gigabit Ethernet, which has extremely strict timing requirements.
• 24.576MHz is a standard frequency for professional audio equipment, where any deviation can affect sound quality.
• 3.6864MHz is often used for UART communication, requiring accurate baud rate generation.

The frequency accuracy demands in these applications far exceed those of ordinary circuits, making spacer installation an essential final-tuning step in the manufacturing process.

Core Function  2: Mechanical Protection for Enhanced Reliability  

The internal quartz wafer of an HC-49/U crystal is very fragile. A spacer, typically made of an elastic material like silicone or rubber, acts as a shock absorber. It dampens external vibration and mechanical shock, preventing the delicate wafer from cracking under stress. Furthermore, it maintains a safe distance between the wafer and the conductive metal casing, preventing potential short circuits caused by casing deformation during assembly or transport. This significantly enhances the long-term reliability of the component, which is vital for crystals used in industrial or automotive applications.

Core Function  3: Environmental Sealing for Long-Term Stability  

A high-quality spacer also serves to   stabilize the crystal's internal environment  . Spacers with excellent airtightness help maintain the hermetic seal of the crystal package, preserving the inert gas (like Nitrogen) fill inside. This effectively blocks moisture and contaminants from entering, which is crucial for slowing the aging process of the crystal and ensuring long-term frequency stability.

Common Frequencies and Application Scenarios  

Based on our production experience, the following HC-49/U crystal frequencies frequently require spacer adjustment for optimal performance:

In summary, adding a spacer to an HC-49/U crystal is a highly effective solution that combines frequency trimming, mechanical protection, and environmental sealing. If you are facing frequency deviation challenges with critical components like 24.576MHz or 25.000MHz crystals, this simple hardware modification can be the perfect solution.

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How Does Megtron 6 M6 Material Solve Signal Loss Challenges in High-Frequency PCBs?

In the race for higher data speeds and greater bandwidth, signal loss is the ultimate enemy. As frequencies climb into the gigahertz range—common in 5G, radar, and high-speed computing—traditional PCB materials like FR-4 become a significant bottleneck. They absorb and degrade signals, leading to data errors, reduced range, and compromised system performance.

Panasonic Megtron 6 M6 laminate is engineered specifically to combat this enemy. It solves signal loss challenges through a fundamental improvement in its core material properties, primarily by minimizing Dielectric Loss and ensuring Impedance Stability. Let's break down the science behind it.

1. Taming the Primary Culprit: Ultra-Low Dielectric Loss (Df)

The most significant source of signal loss at high frequencies is not the conductor but the insulating substrate itself, a phenomenon known as Dielectric Loss.

The Problem with FR-4: Standard FR-4 has a Dissipation Factor (Df) in the range of 0.020 at 1 GHz. Think of Df as a measure of how much electrical energy the substrate converts into wasted heat. A higher Df means the material "absorbs" more of your signal, attenuating it as it travels along the trace.

The Megtron 6 Solution:Megtron 6 M6 boasts an exceptionally low Df of 0.002 at 1GHz and a still-impressive 0.0037 at 13GHz. This is an order-of-magnitude improvement.

Analogy: If FR-4 is a rough, muddy path that saps a runner's energy, Megtron 6 is a smooth, high-tech track. The signal experiences far less resistance from the substrate, allowing it to travel farther and with greater integrity.

Result: This directly translates to lower insertion loss, enabling longer trace lengths, higher data rates (crucial for 400G/800G optics), and more powerful signals in applications like 77GHz automotive radar.

2. Ensuring Predictable Performance: Stable Dielectric Constant (Dk)

The Dielectric Constant (Dk) is a measure of how much the insulating material slows down the electrical signal and affects its impedance. An unstable Dk is a silent killer of signal integrity.

The Problem with Inconsistent Materials: In many materials, the Dk can vary with frequency, temperature, or even the manufacturing lot. This variability makes it incredibly difficult for engineers to design precise impedance-controlled lines (like the 50-ohm traces in our 12-layer PCB). An unexpected shift in Dk during operation can detune your circuit, cause impedance mismatches, and lead to signal reflections.

The Megtron 6 Solution: Megtron 6 high speed PCB offers a stable and predictable Dk of ~3.34 at 13GHz, with minimal change over a wide frequency range. This stability is engineered into the material's composition.

Result: Design engineers can model their high-speed circuits with extreme confidence. The impedance calculated in the simulation (e.g., the 4.31mil trace for a 50-ohm line on L3) will be the impedance fabricated on the actual board. This eliminates guesswork, reduces design iterations, and guarantees that eye diagrams remain open and well-defined.

3. The Combined Effect: Enhanced Signal Integrity and System Bandwidth

The combination of a low Df and a stable Dk is what truly sets Megtron 6 apart. It's not just about losing less signal; it's about preserving the signal's quality.

Lower Attenuation: The low Df directly reduces the amount of signal amplitude lost per unit length.

Minimized Dispersion: The stable Dk ensures that different frequency components of a complex digital signal travel at the same speed. This prevents the "smearing" or spreading out of the signal pulse, which is critical for maintaining the shape of high-speed digital waveforms.

4. Supporting Factors: Thermal and Dimensional Stability

While not directly electrical, Megtron 6's thermal properties play a crucial supporting role in combating long-term performance degradation.

High Tg and Td: With a Glass Transition Temperature (Tg) >185°C and a Thermal Decomposition Temperature (Td) of 410°C, Megtron 6 can withstand the high temperatures of multiple lead-free soldering cycles without breaking down.

Why this matters: If a material degrades thermally during assembly, its Dk and Df can permanently change, altering the performance of the finished PCB from the design intent. Megtron 6's robustness ensures the electrical properties you designed for are the ones you get after manufacturing.

Low CTE: Its controlled Coefficient of Thermal Expansion (16/16/45 ppm/°C) prevents excessive warping or delamination under thermal stress. This maintains the physical geometry of the impedance-controlled traces, which is essential for their consistent electrical performance.

Conclusion: A Material Engineered for the Gigahertz Era

In summary, Megtron 6 M6 solves high-frequency signal loss challenges by providing an ultra-low-loss dielectric "foundation" that is both stable and predictable. It directly attacks the primary sources of loss—dielectric absorption and impedance variation—that plague conventional materials.

By choosing a PCB built with Megtron 6, like the 12-Layer Megtron6-M6 High Speed 2.0mm Thick PCB, you are not just selecting a component; you are choosing a guaranteed level of signal fidelity. This allows your designs to achieve the performance boundaries required for the next generation of 5G infrastructure, autonomous vehicles, and high-performance computing systems.

What Are the Key Benefits of Using F4BTMS450 Material in a 4-Layer RF PCB?

In the world of Radio Frequency (RF) and microwave electronics, the printed circuit board (PCB) substrate is far more than a passive platform for components; it is an integral part of the circuit's performance. Choosing the right material is critical, and for demanding applications, standard FR-4 is insufficient. The F4BTMS450 material represents a specialized high-frequency laminate that offers a suite of compelling advantages for a4-layer RF PCB design.

Here are the key benefits of using F4BTMS450:

1. Superior Signal Integrity with Stable Dielectric Constant

At RF frequencies, signal integrity is paramount. The dielectric constant (Dk orεr) of the substrate material directly controls the impedance of transmission lines (like microstrips and striplines) and the phase of signals. 

• Tight Dk Tolerance: F4BTMS450 has a dielectric constant of 4.5 +/-0.09 at 10GHz. This exceptionally tight tolerance ensures that the impedance is consistent across the entire board and from one batch of boards to the next.

• Benefit: Engineers can design with confidence, achieving precise impedance matching (e.g., 50Ωlines) without unexpected variations that can cause signal reflections, loss of power, and degraded system performance.

2. Extremely Low Loss for Enhanced Efficiency

As signals travel through the 4-layer F4BTMS450 PCB, some energy is absorbed by the dielectric material and converted into heat. This is measured by the Dissipation Factor (Df) or loss tangent.

• Minimal Dielectric Loss: F4BTMS450 boasts an ultra-low dissipation factor of 0.0015 at 10GHz. This is an order of magnitude lower than standard FR-4.

Benefit: For a 4-layer RF PCB, this translates to:

• Higher Efficiency: Less signal power is lost, which is crucial for battery-operated devices and high-power transmitters.

• Improved Signal-to-Noise Ratio (SNR): Cleaner signals with less degradation over distance.

• Better System Performance: In applications like radar and satellite communications, low loss directly increases range and sensitivity.

3. Exceptional Thermal and Dimensional Stability

RF systems, especially power amplifiers, generate heat, and equipment often operates in harsh environments with wide temperature swings.

• Low Coefficient of Thermal Expansion (CTE): F4BTMS450 has a CTE of 12/12/45 ppm/°C (x/y/z). This low and balanced expansion profile is close to that of copper, reducing stress on plated through-holes (vias).

• Stable Dk over Temperature: Its thermal coefficient of Dk is a low -58 ppm/°C. This means the dielectric constant remains stable over a wide temperature range (-55°C to 150°C).

Benefit: The 4-layer PCB structure remains mechanically reliable, preventing via cracking and delamination. Electrically, the circuit performance (e.g., filter center frequency, phase response) remains predictable and stable regardless of operational temperature, which is vital for aerospace and defense applications.

4. High Reliability for Demanding Environments

The operational environment for many RF applications is unforgiving. F4BTMS450 is engineered to meet these challenges.

• Low Moisture Absorption (0.08%): Moisture ingress can drastically alter a material's Dk and increase loss. The very low moisture absorption of F4BTMS450 high frequency PCB ensures stable electrical performance even in humid conditions.

• UL-94 V0 Flammability Rating: The material is self-extinguishing, enhancing the safety and reliability of the end-product.

Benefit: This combination makes the resulting 4-layer PCB highly reliable and suitable for critical systems in aerospace, spaceflight, and military radar, where failure is not an option.

5. Optimal Performance for Complex, Dense 4-Layer Designs

The specific construction of a 4-layer board using F4BTMS450 leverages all the benefits above into a practical, high-performance multilayer solution.

• Improved EMI Shielding: A typical4-layer stackup (Signal-Ground/Power-Signal) allows for dedicated ground planes. These planes act as shields, containing RF energy within the board and protecting sensitive signals from external noise.

• Enhanced Power Integrity: The solid internal power plane provides a low-inductance power distribution network, which is crucial for stable voltage to high-speed digital and RF components.

• Material Consistency in Multilayer Bonding: The use of compatible prepreg (likeRO4450F) in the stackup ensures a homogeneous dielectric environment, maintaining consistent electrical properties throughout all four layers.

Conclusion: A Foundation for High-Frequency Success

In summary, selecting F4BTMS450 for a 4-Layer RF PCB is a strategic decision to build your design on a foundation of performance, stability, and reliability. Its key benefits—stable dielectric constant, extremely low loss, outstanding thermal performance, and high environmental resilience—directly address the most critical challenges in RF and microwave design. By minimizing electrical losses and maintaining predictable behavior under stress, this material enables the creation of superior, high-performance systems for the most demanding applications in aerospace, telecommunications, and defense.

With the rapid expansion of new energy, mining, metallurgy, and electroplating industries, nickel pollution in water bodies has become a growing threat to environmental quality and human health. During industrial processes, nickel ions often interact with various chemical additives to form highly stable heavy-metal organic complexes (HMCs). In nickel electroplating, for example, citrate (Cit) is widely used to improve coating uniformity and brightness, but the two carboxyl groups in Cit readily coordinate with Ni²⁺ to form Ni–Citrate (Ni-Cit) complexes (logβ = 6.86). These complexes significantly alter nickel’s charge, steric configuration, mobility, and ecological risks, while their stability makes them challenging to remove with conventional precipitation or adsorption methods.

Currently, "complex dissociation" is regarded as the key step in removing HMCs. However, typical oxidation or chemical treatments suffer from high cost and complicated operation. Therefore, multifunctional materials with both oxidative and adsorptive capabilities offer a promising alternative.

Researchers from Beihang University, led by Prof. Xiaomin Li and Prof. Wenhong Fan, used the CIQTEK scanning electron microscope (SEM) and electron paramagnetic resonance (EPR) spectrometer to conduct an in-depth investigation. They developed a new strategy using KOH-modified Arundo donax L. biochar to efficiently remove Ni-Cit from water. The modified biochar not only showed high removal efficiency but also enabled nickel recovery on the biochar surface. The study, titled “Removal of Nickel-Citrate by KOH-Modified Arundo donax L. Biochar: Critical Role of Persistent Free Radicals”, was recently published in Water Research.

Material Characterization

Biochar was produced from Arundo donax leaves and impregnated with KOH at different mass ratios. SEM imaging (Fig. 1) revealed:

• The original biochar (BC) exhibited a disordered rod-like morphology.

• At a 1:1 KOH-to-biomass ratio (1KBC), an ordered honeycomb-like porous structure was formed.

• At ratios of 0.5:1 or 1.5:1, pores were underdeveloped or collapsed.

• BET analysis confirmed the highest surface area for 1KBC (574.2 m²/g), far exceeding other samples.

SEM and BET characterization provided clear evidence that KOH modification dramatically enhances porosity and surface area—key factors for adsorption and redox reactivity.

Figure 1. Preparation and characterization of KOH-modified biochar.

Performance in Ni-Cit Removal

Figure 2.
(a) Removal efficiency of total Ni by different biochars;
(b) TOC variation during Ni–Cit treatment;
(c) Effect of Ni–Cit concentration on the removal efficiency of 1KBC;
(d) Effect of pH on the removal performance of 1KBC;
(e) Influence of coexisting ions on Ni–Cit removal by 1KBC;
(f) Continuous-flow removal performance of Ni–Cit by 1KBC.
(Ni–Cit = 50 mg/L, biochar dosage = 1 g/L)

Batch experiments demonstrated strong removal performance:

• At 50 mg/L Ni-Cit and 1 g/L material dosage, 1KBC removed 99.2% of total nickel within 4 hours, compared to 32.6% for BC.

• TOC removal reached 31% for 1KBC, confirming that Ni-Cit undergoes complex dissociation followed by Ni²⁺ adsorption.

• Even at 100 mg/L Ni-Cit, the removal efficiency remained above 93%.

• 1KBC maintained excellent performance across a wide pH range (pH > 5).

• Phosphate significantly inhibited removal due to solution acidification and competitive complexation with Ni²⁺.

• In continuous-flow tests, a 1KBC-packed fixed-bed reactor operated for 6900 minutes, treating 460 bed volumes, while maintaining effluent Ni < 0.5 mg/L.

Post-Treatment Material Characterization

Figure 3. Morphology and EDS comparison of the material before (a) and after (b) Ni–Cit removal;
(c) XPS spectra of surface Ni 2p after the removal process.

Recovered biochar (R1KBC) showed:

• No significant morphological changes.

• Uniform Ni distribution confirmed by EDS mapping.

• XPS spectra displayed both Ni²⁺ and Ni³⁺ peaks, direct evidence of oxidative complex dissociation.

EPR-Based Identification of ROS

Figure 4. EPR measurements:
(a) TEMP-trapped ¹O₂ generated by biochar;
(b, c) BMPO-trapped •OH and O₂•⁻ generated by biochar;
(d) Hyperfine splitting fitting analysis of the 1KBC signal in panel (c).

Using the CIQTEK EPR spectrometer, the team identified reactive oxygen species (ROS) generated on the biochar surface:

• ¹O₂: strong TEMP–¹O₂ triple signal (1:1:1, AN = 17.32 G) observed only in 1KBC.

• OH: BMPO–•OH quartet detected in both BC and 1KBC, but much stronger in 1KBC.

• O₂•⁻: identified through BMPO–•OOH signals in methanol-containing systems.

1KBC produced significantly higher levels of ¹O₂, •OH, and O₂•⁻ than BC, confirming the enhanced redox activity induced by KOH modification.

Free Radical Quenching Experiments

Figure 5.
(a) Effect of ¹O₂; (b) •OH; and (c) O₂•⁻ on Ni–Cit removal efficiency;
(d) Inhibition rates of different ROS on Ni–Cit removal.

By introducing quenchers, FFA (¹O₂), p-BQ (O₂•⁻), and methanol (•OH)—the team quantified the contributions of different ROS:

O₂•⁻ inhibition (55%) > ¹O₂ inhibition (17%) > •OH inhibition (12%)

This ranking indicates that O₂•⁻ plays the dominant role in Ni-Cit degradation and complex dissociation.

Role of PFRs and ROS Generation Mechanism

Figure 6.
(a) Detection of surface PFRs in biochar;
(b) Effect of PFR quenching on Ni–Cit removal by biochar;
(c) ¹O₂, (d) •OH, and (e) O₂•⁻ signals in 1KBC and TEA-treated samples;
(f) Schematic of ROS transformation pathways.

Persistent free radicals (PFRs) in biochar are closely linked to ROS formation. EPR results showed:

• 1KBC exhibited much higher PFR concentration than BC.

• PFRs had a g-value of 2.0034, characteristic of carbon-centered radicals adjacent to oxygen (e.g., phenoxy radicals).

• Triethylamine (TEA) effectively quenched PFRs, reducing Ni-Cit removal efficiency to ~50% and drastically lowering ROS levels.

The mechanism (Fig. 6f):

• Dissolved oxygen adsorbs onto the biochar surface.

• PFRs transfer electrons to O₂, forming O₂•⁻.

• O₂•⁻ initiates complex dissociation; subsequent ROS degrade the citrate ligand.

DFT Calculations and Mechanistic Insights

Figure 7.
(a) Optimized structure of Ni–Cit;
(b) Electrostatic potential (ESP) map;
(c) HOMO; (d) LUMO;
Fukui function isosurfaces of Ni–Cit:
(e) f⁻, (f) f⁺, (g) f⁰, (h) condensed dual descriptor (CDD), and (i) Fukui indices;
(j) Proposed degradation pathways of Ni–Cit.

Density functional theory (DFT) calculations clarified the molecular reaction pathways:

• Frontier molecular orbital and Fukui function analysis revealed that the Ni center is prone to nucleophilic attack, while the citrate ligand undergoes electrophilic reactions.

• O₂•⁻, with its strong nucleophilicity, targets the Ni center, breaking the Ni–Cit coordination.

• Citrate ligands degrade through two ROS-mediated pathways.

These theoretical results align with EPR findings and support the proposed mechanism.

KOH-modified biochar (1KBC) achieved 99.2% Ni removal from 50 mg/L Ni-Cit solution within 4 hours. The modification significantly enhanced porosity, surface functionality, and, critically, the concentration of persistent free radicals. These PFRs activated dissolved oxygen to generate ROS, among which O₂•⁻ acted as the primary species driving Ni-Cit dissociation. Subsequent ROS degraded the citrate ligand, while released Ni²⁺ was adsorbed onto the biochar.

This study demonstrates a sustainable "one-step dissociation and recovery" approach for treating metal–organic complexes, offering strong potential for future real-world applications.