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When it comes to high-frequency PCB design, the material choice often dictates success or failure. This 2-layer board, built on Rogers RO4835, strikes an impressive balance between RF performance and manufacturing practicality. Let's break down why this design works and why it matters for engineers working on automotive radar, microwave links, and power amplifiers. The Material That Makes It Possible RO4835 is essentially the more thermally stable cousin of Rogers' well-known RO4350B. The key differentiator is oxidation resistance. Traditional thermoset microwave materials can degrade when exposed to repeated thermal stress. RO4835 holds up significantly better, maintaining consistent dielectric properties through multiple soldering cycles. The numbers speak for themselves. With a dielectric constant of 3.48 ± 0.05 and a dissipation factor of 0.0037 at 10 GHz, this material delivers the low-loss performance required for circuits operating well into the microwave spectrum. The tight Dk tolerance of ±0.05 is particularly valuable—it means controlled impedance lines stay predictable across production batches, eliminating the need for post-production tuning. Thermally, RO4835 is a beast. The glass transition temperature exceeds 280°C. This isn't just a number on a datasheet. It translates to real-world reliability during lead-free soldering. No blistering. No delamination. Just consistent performance through the harsh temperature profiles of modern assembly processes. The material also carries a UL 94 V-0 flammability rating and meets IPC-4103 specifications, making it suitable for safety-critical applications. The coefficient of thermal expansion deserves attention too. At 31 ppm/°C in the Z-axis, plated through-holes experience less stress during thermal cycling. This directly impacts long-term reliability, especially in automotive applications where temperature swings from -40°C to +125°C are routine. The low in-plane expansion (10 ppm/°C on X-axis, 12 ppm/°C on Y-axis) ensures dimensional stability throughout circuit processing, from lamination through reflow soldering. When materials expand and contract at different rates, via barrels can crack and inner-layer connections can fail. RO4835 minimizes this risk. Another critical advantage is the LoPro reverse-treated copper foil available with RO4835. This proprietary foil treatment reduces conductor surface roughness, which in turn reduces insertion loss at high frequencies. At 10 GHz and above, skin effect concentrates current at the conductor surface. Rough copper increases the effective path length and adds resistive losses. LoPro foil minimizes this effect, preserving signal amplitude through transmission lines.       A Stack-Up That Keeps It Simple This is a no-frills 2-layer design. The core is 0.508 mm of RO4835, sandwiched between 1 oz copper on both sides. Total board thickness comes in at 0.6 mm. The dimensions—45 mm by 83.69 mm with ±0.15 mm tolerance—fit neatly into compact RF modules where space is at a premium. Minimum trace width is 5 mils with 6 mils spacing, which supports controlled impedance lines while staying within standard fabrication capabilities. For a 50-ohm microstrip line on RO4835 with a 0.508 mm dielectric thickness, the trace width would be approximately 0.95 mm. This is a comfortable geometry that balances impedance control with manufacturability. The design rules are achievable with standard etching processes, avoiding the yield penalties associated with ultra-fine features. The minimum hole size of 0.2 mm accommodates standard via drill sizes and through-hole component leads. The design incorporates 9 plated through-hole vias, each with a minimum copper plating thickness of 20 µm. This plating thickness is verified through microsection analysis per IPC-TM-650 2.2.18, ensuring sufficient current-carrying capability and mechanical robustness. No blind vias and no buried vias are specified, which simplifies the fabrication sequence and reduces manufacturing cost. For a 2-layer board, there is simply no need for these advanced via structures. The "No Solder Mask" Decision This might raise eyebrows for engineers accustomed to conventional PCB practices, but the absence of solder mask on both outer layers is a deliberate choice for high-frequency performance. Solder mask isn't electrically neutral. It introduces dielectric loss and has uncontrolled permittivity that can perturb characteristic impedance. The dissipation factor of typical solder mask materials ranges from 0.02 to 0.08—an order of magnitude higher than RO4835's 0.0037. This means even a thin layer of solder mask can add measurable insertion loss, particularly at frequencies above 5 GHz. For microwave circuits, this is unacceptable. Removing the mask eliminates this variable entirely, ensuring that the circuit's electrical performance is determined solely by the controlled dielectric of RO4835. Additionally, solder mask thickness and dielectric constant can vary across the board and from batch to batch. This variability introduces inconsistency in impedance-controlled lines, complicating design validation and production testing. Without solder mask, there are no such variations. The designer achieves consistent, predictable performance across every board. The trade-off is cosmetic—boards won't have that polished green finish—but the electrical benefits are clear. In RF engineering, function trumps appearance. Surface Finish and Silkscreen Immersion gold (ENIG) is specified over electroless nickel. Nickel thickness ranges from 3 to 6 µm with gold thickness of 0.05 to 0.10 µm, compliant with IPC-4552. ENIG provides excellent solderability, corrosion resistance, and a flat surface for component attachment. The planar nature of the finish is particularly important for surface-mount components, ensuring consistent solder joint formation. The finish is compatible with both soldering and wire bonding, giving assembly flexibility. The gold layer protects the nickel from oxidation, ensuring a fresh, solderable surface even after extended storage. ENIG is widely used in the industry and is supported by all major assembly houses. Black silkscreen appears on the top layer only for component identification and reference designator marking. Bottom layer has no legend, reducing unnecessary steps in fabrication. Silkscreen is strictly excluded from pad areas to prevent contamination. Solder paste will not wet properly over silkscreen ink, and even small ink residues can lead to voiding, head-in-pillow defects, or poor wetting. Excluding silkscreen from pads is a simple but important design discipline. Built to IPC Class 2 This isn't aerospace-grade Class 3, and it's not meant to be. IPC Class 2 is appropriate for general-purpose electronic products requiring moderate reliability. Minor cosmetic imperfections are acceptable, but all functional requirements—continuity, insulation resistance, thermal performance—are strictly enforced. Class 2 provides a practical middle ground. It ensures quality without imposing the extreme requirements of Class 3, which would add cost without necessarily improving performance for this application. The standard specifies hole wall quality, minimum annular ring, and cleanliness levels that are achievable with standard manufacturing processes while still guaranteeing reliable operation. Every board undergoes 100% electrical testing before shipping. Flying-probe or fixture-based systems verify continuity of all nets, isolation between non-connected nets, and detection of opens or shorts. No defective units leave the factory. This comprehensive screening ensures that every board functions as designed, supporting worldwide distribution without requiring additional inspection at the customer site. Where This PCB Shines Automotive radar is the obvious use case—24 GHz and 77 GHz systems where low loss and thermal stability are non-negotiable. The material handles the harsh under-hood environment, while the straightforward design keeps costs manageable. Radar sensors are increasingly common in modern vehicles for adaptive cruise control, collision avoidance, and blind-spot detection. These systems must operate reliably in extreme temperatures, vibration, and humidity. RO4835 delivers that reliability. Beyond automotive, this PCB is suitable for point-to-point microwave links, power amplifiers, phased-array radar, and general RF components like filters and couplers. The material's low loss and tight Dk tolerance enable consistent performance in these demanding applications. The Bottom Line This 2-layer board demonstrates that high-frequency design doesn't always require exotic PTFE materials or complex multilayer stack-ups. RO4835 delivers the electrical performance needed for demanding microwave applications while remaining compatible with standard FR-4 fabrication processes. The result is a cost-effective solution for performance-sensitive, high-volume production. No unnecessary complexity. No over-engineering. Just good design decisions backed by solid material science. For engineers working on automotive radar or similar RF applications, this design offers a proven reference point—one that balances performance, reliability, and manufacturability in equal measure. And in the competitive world of automotive electronics, that balance is what separates successful products from also-rans.

What do you do when your RF design demands high-frequency performance, but your budget cannot accommodate the specialized processing of PTFE materials? You build a hybrid PCB. You combine a high-performance RF laminate for the critical signal layers with a standard FR-4 core for the rest. You get the best of both worlds: premium electrical characteristics and affordable fabrication. Today I am looking at a 6-layer hybrid rigid PCB that does exactly that. It pairs RO4003C hydrocarbon ceramic material with Tg170°C FR-4, delivering controlled impedance, blind vias, and IPC-Class-3 reliability in a single board. Let me walk you through the construction. Construction Overview: A 6-Layer Hybrid Construction This is a 6-layer rigid PCB measuring 127mm by 103mm, including the process edge. The finished lamination thickness is 1.74mm, with 1oz of finished copper on every conductive layer. The stackup is what makes this board interesting. It combines two material families: RO4003C core – a glass-reinforced hydrocarbon ceramic thermoset laminate for high-frequency layers Tg170°C FR-4 prepreg and core – standard FR-4 material for the remaining layers This hybrid approach allows the designer to place the critical RF signal paths on the RO4003C layers while using lower-cost FR-4 for power distribution, ground planes, and less sensitive signals. The surface finish is hard electrolytic gold plating – a robust choice for boards requiring good wear resistance and long shelf life. Both sides have green solder mask with white silkscreen legend. The board includes blind vias connecting L1-L2 and L5-L6, with a hole copper thickness of 25μm. Full controlled impedance circuitry is implemented across the board. Quality standard is IPC-Class-3, the highest reliability class for high-performance electronic equipment. RO4003C: The RF Core of the Hybrid Let me focus on the star material – RO4003C – because this is what makes the board's high-frequency performance possible. RO4003C is Rogers' glass-reinforced hydrocarbon ceramic thermoset laminate. It is designed specifically for high-frequency circuits operating above 500MHz, where standard FR-4 can no longer meet RF electrical requirements. Why choose RO4003C over PTFE-based laminates? The answer is simple: processability. Unlike PTFE materials, RO4003C requires no specialized sodium etching via pretreatment. It is fully compatible with standard FR-4 manufacturing processes – drilling, desmear, copper plating, and etching can all be done using conventional equipment. This dramatically reduces fabrication cost and lead time, while still delivering premium RF performance. Electrical performance is solid. The material maintains a stable dielectric constant across a wide frequency range, with an ultra-low temperature coefficient of dielectric constant (TCDK). This means your impedance-controlled transmission lines will stay consistent across temperature variations – critical for broadband RF and microwave circuits. Thermal properties are equally impressive. With a glass transition temperature (Tg) exceeding 280°C, RO4003C maintains stable thermal properties throughout the entire PCB fabrication thermal cycle – including multiple lamination steps for the hybrid stackup. The CTE value matches copper foil closely, ensuring excellent dimensional stability. The low Z-axis CTE secures plated through-hole integrity even under severe thermal shock conditions. Optional LoPro® copper foil is available to further minimize insertion loss for broadband applications. For this design, standard copper foil is used, but the option exists for even more demanding applications. Understanding the Hybrid Approach Why go hybrid rather than using RO4003C for all six layers? The answer is cost optimization. RO4003C is more expensive than FR-4. By using it only where it is needed – typically the outer signal layers or critical RF routing layers – and using FR-4 for inner layers that carry power, ground, or lower-speed signals, you get the RF performance you need without paying for premium material where it is not necessary. The Tg170°C FR-4 used in this design is itself a high-performance FR-4 variant. Standard FR-4 has a Tg of around 130-140°C. Tg170°C FR-4 offers better thermal stability, making it compatible with the RO4003C lamination process and ensuring the hybrid board can withstand multiple thermal cycles during fabrication and assembly. Process Features: Blind Vias The board includes blind vias connecting L1-L2 and L5-L6. These are not through vias that penetrate the entire stackup – they stop at the second and fifth layers respectively. Why use blind vias? Three reasons: Increased routing density – blind vias free up routing space on the inner layers Reduced via stub effects – shorter via stubs mean better signal integrity at high frequencies Improved power distribution – blind vias can connect surface components directly to inner power or ground layers without crossing the entire board The 25μm hole copper thickness is standard for IPC-Class-3 requirements, ensuring robust mechanical and electrical connections. Controlled Impedance: A Requirement, Not an Option Full controlled impedance circuitry is specified for this board. At RF and microwave frequencies, impedance mismatch causes signal reflections, power loss, and degraded performance. Controlled impedance ensures that the characteristic impedance of each transmission line matches the source and load impedances – typically 50Ω for RF systems. The combination of RO4003C's tight Dk tolerance and the hybrid stackup design allows the fabricator to achieve precise impedance control. The laminating process with RO4003C ensures consistent dielectric thickness and Dk across the critical signal layers. Hard Electrolytic Gold: A Robust Surface Finish Hard electrolytic gold plating is specified for this design. Unlike soft gold or ENIG (electroless nickel immersion gold), hard gold contains cobalt or nickel hardeners, making it more durable and wear-resistant. This surface finish is ideal for: Boards with high mating cycle requirements (such as edge connectors) Applications requiring long shelf life Environments where corrosion resistance is critical The trade-off is that hard gold is more expensive than ENIG, but for high-reliability applications, the durability is well worth the cost. Quality Standard: IPC-Class-3 This board is manufactured to IPC-Class-3, the highest reliability class defined by the IPC standards. Class-3 boards are required for: Aerospace and military equipment Medical devices Automotive safety systems High-reliability infrastructure equipment Class-3 requirements include stricter tolerances on hole copper thickness (25μm vs. Class-2's 20μm), tighter inspection criteria, and more rigorous testing. The 100% electrical test and full impedance control specified for this board are consistent with Class-3 expectations. Typical Applications Based on the material combination and design features, this hybrid PCB is well-suited for: Broadband RF and microwave communication circuits Controlled impedance transmission lines and signal matching networks Commercial radar, antenna, and wireless transceiver modules Base station radio units and wireless communication infrastructure Multi-layer mixed-dielectric high-frequency PCBs High-frequency sensing and industrial RF devices Design Considerations If you are considering a similar hybrid design, here are a few points to keep in mind. Material compatibility is critical. RO4003C and FR-4 have different CTE values. While RO4003C is designed to match copper closely, FR-4's CTE is slightly different. The lamination process must be carefully controlled to minimize stress between layers. The Tg170°C FR-4 used in this design helps by providing better thermal matching than standard FR-4. Blind via registration requires precision. With six layers and two pairs of blind vias (L1-L2 and L5-L6), registration accuracy is essential. Misalignment can cause opens or shorts. Your fabricator must have experience with sequential lamination and blind via formation. Controlled impedance tolerance depends on the prepreg thickness. In a hybrid stackup, the dielectric thickness between layers is determined by the prepreg thickness. Variations in prepreg thickness directly affect impedance. Work with your fabricator to define acceptable tolerance ranges early in the design phase. Final Thoughts This 6-layer hybrid PCB demonstrates a practical approach to high-frequency design: use a premium RF laminate where it matters, pair it with cost-effective FR-4 where it does not, and leverage FR-4 processability to keep fabrication costs under control. RO4003C delivers the electrical performance – stable Dk, low loss, excellent thermal stability – without the processing headaches of PTFE. The blind vias add routing density and improve signal integrity. The IPC-Class-3 standard ensures the board can withstand the most demanding applications. And the hard gold finish provides long-term durability. If your next RF design requires controlled impedance, multilayer integration, and cost-effective production, this hybrid approach is well worth considering. Have you worked with hybrid stackups combining RO4003C and FR-4 before? What challenges did you encounter with material matching or blind via registration? Drop your experience in the comments.  

What happens when you remove the solder mask, remove the silkscreen, and even remove the glass fiber cloth from the substrate? You get a board that is built for one thing only: clean, predictable, high-frequency performance.   Today I am looking at a two-layer rigid PCB built on TFA294 – a PTFE-ceramic composite from the TFA series. This is not your standard RF laminate. It contains no glass fiber cloth, minimizes anisotropy, and delivers a dissipation factor of just 0.0010 at 10GHz. Let me walk you through the design.   PCB Overview: Simple Structure, Serious Intent The board measures 97.53mm by 100.28mm. Finished thickness is 1.1mm, with 1oz of copper on both outer layers (approximately 35μm). The minimum trace width is 4 mils with 6 mil spacing, and the smallest drilled hole size is 0.35mm. There are no blind vias. Via plating thickness is 20μm, and every board undergoes 100% electrical testing before shipment. The surface finish is Immersion Gold – a solid, reliable choice for RF work.   Like several designs I have covered recently, this board has no solder mask and no silkscreen on either side. That is becoming a familiar theme for high-performance RF boards: remove the variables, remove the uncertainty.   TFA294: A Different Kind of PTFE Laminate Now let me focus on the material, because TFA294 is genuinely different from most PTFE-based laminates on the market.   The TFA series uses a dielectric layer composed of PTFE resin and ceramics. But here is the key difference: it contains no glass fiber cloth. Traditional PTFE laminates like RT/duroid are reinforced with woven fiberglass. That glass reinforcement does two things – it adds mechanical strength, but it also introduces microscopic inhomogeneities. When electromagnetic waves propagate through glass fibers, they scatter and distort. The effect is small, but at higher frequencies and in sensitive applications, it matters.   TFA eliminates the glass fiber entirely. Instead, it uses a new process to create prepreg sheets with uniformly dispersed nano-ceramics. The result is a material with minimal X/Y/Z anisotropy. The electrical properties are the same in every direction. No fiberglass weave effect. No unexpected variations.   Electrical Performance: Low Loss, Stable Dk For TFA294, the numbers are impressive.   At 10GHz, the dielectric constant (Dk) is 2.94. At 20GHz, the dissipation factor (Df) is just 0.0010 – that is exceptionally low. Even at 40GHz, the Df remains low at 0.0012. This material will not eat your signal, even at millimeter-wave frequencies.   The temperature coefficient of dielectric constant (TCDK) is -5 ppm/°C across the range of -55°C to 150°C. That is outstanding. For comparison, many standard RF materials have TCDK values in the range of -20 to -50 ppm/°C. A TCDK of -5 ppm/°C means the dielectric constant barely moves with temperature. Your antenna will not drift significantly between a cold morning and a hot afternoon.   Thermal and Mechanical Properties The thermal and mechanical numbers are equally solid.   Coefficients of thermal expansion are 18 ppm/°C on both the X and Y axes, and 32 ppm/°C on the Z axis. The X/Y values match copper very well – copper sits at approximately 17 ppm/°C. This close match reduces stress on plated through-holes and surface mount pads during thermal cycling.   Thermal conductivity is 0.59 W/m·K. That is roughly double that of standard FR-4, helping with power dissipation in amplifier or feed network applications.   Moisture absorption is just 0.03 percent – extremely low. PTFE materials are naturally hydrophobic, and the ceramic loading does not change that. This board will maintain stable performance even in humid environments.   Flammability rating is UL 94-V0, meeting standard safety requirements for most aerospace and defense applications.     Why No Glass Fiber Matters I want to spend a moment on the glass-free construction because it is genuinely important.   Traditional PTFE/ceramic laminates use glass fiber cloth as a reinforcement. The glass fibers have a different dielectric constant than the PTFE-ceramic mixture. As an electromagnetic wave travels across the board, it encounters these fibers and scatters. The effect is called "fiber weave effect" or "glass weave effect." At lower frequencies, it is negligible. At microwave frequencies and above, it can cause phase variations across an array – a disaster for phased array antennas.   By removing the glass fiber entirely, TFA294 eliminates this problem. The dielectric constant is uniform across the entire board. Every patch antenna in a phased array sees the same electrical environment. Phase consistency improves. Beamforming becomes more precise.   The combination of ultra-low loss, stable Dk across temperature, matched CTE to copper, and glass-free construction makes this material suitable for applications where failure is not an option: space equipment, airborne radar, satellite communications, and navigation systems.   Typical Applications Aerospace equipment, space systems, cabin electronics, and aircraft Microwave circuits, antennas, and phase-sensitive antennas Early warning radar and airborne radar systems Phased array antennas and beamforming networks Satellite communications and navigation equipment Power amplifiers   A Few Practical Notes Before you take this design into production, here are a few things to keep in mind.   First, like all PTFE-based materials, TFA294 requires special hole preparation. The PTFE surface is chemically inert. Standard FR-4 desmear processes will not work. Your fabricator must use plasma or sodium naphthalene treatment before copper plating. Confirm this capability upfront.   Second, the no-mask design means the copper is fully exposed. Immersion gold provides protection, but the board should be handled with care. Clean gloves, sealed storage, and careful assembly are essential.   Third, the material contains no glass fiber cloth. This is a benefit for electrical performance, but it does mean the board may be slightly less rigid than glass-reinforced alternatives at the same thickness. At 1.1mm thickness, this is unlikely to be an issue, but it is worth noting for very large panels or rough handling conditions.   Final Thoughts This two-layer TFA294 board is a study in purposeful design. Remove the mask. Remove the silkscreen. Remove the glass fiber. Keep only what matters: low loss, stable Dk, matched CTE, and clean signal propagation.   Is TFA294 a direct replacement for established materials like Rogers RT/duroid? That depends on your specific requirements. But for aerospace, radar, and satellite applications where glass weave effect is a real concern and temperature stability is critical, this material deserves serious consideration.   Have you worked with glass-free PTFE-ceramic composites before? How did they compare to traditional woven-reinforced laminates in your application?  

When high-frequency design meets space constraints, a purely planar layout often falls short. That is when you need to think vertically – blind vias, controlled depth slots, and multilayer hybrid laminates come into play.   The board I am looking at today is a perfect example. Built on a combination of Rogers RO3210 and RO4450F, this four-layer structure features controlled depth slots and blind vias, specifically designed for space-constrained high-frequency applications.   Construction Overview: A Four-Layer Hybrid Construction Let me start with the basic parameters. The board measures 95mm by 98mm and uses a four-layer copper structure.   The stackup is quite representative:   Core 1: 0.508mm RO3210 Bondply: 0.2mm RO4450F Core 2: 0.508mm RO3210   Total laminated thickness: 1.321mm   For the copper configuration, the outer layers have a finished copper weight of 1oz (approximately 35μm), while the inner layers use 0.5oz (approximately 18μm). The surface finish is a combination of Immersion Silver and Immersion Gold.   On the cosmetic side, the top layer has green solder mask with white silkscreen. The bottom layer has green solder mask but no silkscreen.   Two process features deserve special attention:   Controlled depth slot: From the top layer down to inner layer 1 (a slot that stops between L1 and L2)   Blind via: 1-3 layer blind via (drilled from L1 to L3 without penetrating the entire board)     RO3210: A High-Dielectric-Constant Ceramic-Filled PTFE RO3210 is the high-Dk member of Rogers' RO3200 series. This series is an extension of the RO3000 family, with the key advantage of maintaining high-frequency performance while improving mechanical stability.   Let me share the core parameters. At 10GHz, RO3210 offers a dielectric constant (Dk) of 10.2 ± 0.50, with a design Dk value reaching 10.8. The dissipation factor (Df) is 0.0027, placing it in the low-loss category for PTFE materials.   Why choose a high Dk? A higher dielectric constant means a shorter wavelength on the board. For a given frequency, the wavelength on a board with Dk of 10.2 is approximately one third of the wavelength in air. This allows antennas and resonant structures to be significantly smaller – a valuable advantage in space-constrained applications.   On the thermal and mechanical side, RO3210 has a decomposition temperature (Td) exceeding 500°C, easily handling lead-free soldering temperatures. The X and Y axis coefficients of thermal expansion (CTE) are 13 ppm/°C, matching well with copper (approximately 17 ppm/°C). The Z-axis CTE is 34 ppm/°C – a very respectable number for a PTFE-based material. Thermal conductivity is 0.81 W/m·K, which helps with power dissipation.   Typical applications for RO3210 include microstrip patch antennas, satellite communication systems, automotive collision avoidance radar, wireless communication base stations, and power amplifier modules.   RO4450F: The "Glue" for High-Frequency Hybrid Lamination In high-frequency multilayer boards, the bonding layer between cores is critical. RO4450F was designed exactly for this purpose – it is a bondply from the RO4400 series, specifically intended for hybrid lamination with RO4000 series materials.   Here are the key parameters. At 10GHz, the Dk is 3.52 ± 0.05 and the Df is 0.0040. The X-axis CTE is 19 ppm/°C, the Y-axis is 17 ppm/°C, and the Z-axis is 50 ppm/°C. Moisture absorption is just 0.09%, and thermal conductivity is 0.65 W/m·K.   Why choose RO4450F instead of standard FR-4 prepreg? The answer lies in CTE matching. RO3210 has an X/Y CTE around 13 ppm/°C. While FR-4's X/Y CTE is typically in the 14-16 ppm/°C range, the Z-axis CTE difference is substantial. RO4450F has a Z-axis CTE of 50 ppm/°C, significantly lower than the 70-80 ppm/°C of standard FR-4. This dramatically reduces the risk of via failure during thermal cycling.   Additionally, RO4450F is compatible with FR-4 processing. It can be laminated using standard processes, without the special treatments required for PTFE-based bonding materials.   Understanding the Process Features Controlled Depth Slot (Top to Inner Layer 1) A controlled depth slot is a milling operation that does not go through the entire board. In this design, the slot stops between the top layer and inner layer 1. Why would you do this? Possible reasons include embedding a component, increasing creepage distance, or improving heat dissipation. One thing to keep in mind: depth tolerance for controlled depth slots is typically around +/- 0.1mm. I recommend adding a comfortable margin in your design.   Blind Via 1-3 A blind via connects layer 1 and layer 3, skipping layer 2 entirely. Compared to a through via, this design offers three advantages: it frees up routing space on layer 2, eliminates the stub effect on the signal via, and increases routing density. The trade-off is increased process complexity and cost – blind vias require sequential lamination and cannot be drilled in a single operation.     Design Considerations and Risk Points CTE Matching While the X/Y CTE of both RO3210 and RO4450F matches copper reasonably well, differences remain in the Z-axis direction. The blind vias and through vias in this four-layer structure will go through multiple thermal cycles. I suggest using thermal stress relief designs around critical vias.   Hybrid Lamination Process RO3210 is a PTFE-based material, while RO4450F belongs to the hydrocarbon resin system. These two material families have different lamination parameters, requiring an experienced fabricator. The PTFE surface must undergo plasma treatment to achieve good adhesion with RO4450F.   Controlled Depth Slot Accuracy With 0.508mm RO3210 plus 0.2mm RO4450F, the total thickness is approximately 1.3mm. The controlled depth slot needs to stop precisely between L1 and L2 – a depth of roughly 0.5 to 0.7mm. This level of precision demands good equipment. I recommend confirming your fabricator's capability before moving to production.   Typical Application Scenarios Based on the material combination and process features, this board could be used in several application areas:   Space-constrained phased array antenna elements   RF front-end modules requiring embedded components   Multilayer feed networks   High-density satellite communication assemblies   Automotive millimeter-wave radar RF boards   Final Thoughts This four-layer RO3210 plus RO4450F design demonstrates an important trend in RF PCB engineering: balancing material performance, manufacturing cost, and integration density.   The high Dk of RO3210 provides the foundation for miniaturization. RO4450F as a bondply solves the CTE compatibility challenge in hybrid lamination. And the controlled depth slot combined with blind vias further compresses the vertical space.   Of course, this type of design places high demands on the fabricator's process capability. Hybrid lamination of PTFE and hydrocarbon materials, depth control of slots, and alignment accuracy of blind vias are all critical points to discuss thoroughly with your fab house before prototyping.   If your project is facing challenges with miniaturization and multilayer integration, this design approach is worth considering.   Have you run into any issues when designing or producing hybrid laminated boards? Feel free to share your experience in the comments.

Today I want to talk about a somewhat unusual PCB. What makes it unusual is not a high layer count or complex manufacturing processes — quite the opposite. This is a two-layer board with no solder mask and no silkscreen, yet it is specifically designed for high-frequency antenna applications.   The core material is WL-CT440, a domestically produced high-frequency laminate from Wangling. If you are looking for an alternative to Rogers or PTFE materials, this article might give you some new ideas.   Construction Overview: Minimalist but Not Simple Let us start with the basic parameters. The board measures 89mm by 63.5mm and uses a two-layer construction. The finished board thickness is 0.8mm, with 1oz or 35μm of finished copper weight on the outer layers. The minimum trace width is 4 mils and the minimum spacing is 6 mils. The smallest hole size is 0.2mm, and there are no blind vias. Every board undergoes 100% electrical testing before shipment.   Now let me highlight the statistics. The board contains 37 components and 49 pads in total, consisting of 27 thru-hole pads and 22 surface mount pads all located on the top layer — no SMT pads are placed on the bottom layer. There are 31 vias and only 2 nets. This is a typical high-frequency or antenna topology: simple in structure but demanding in performance.   Why No Solder Mask and No Silkscreen? The most distinctive feature of this board is the complete absence of both solder mask and silkscreen — nothing on the top layer and nothing on the bottom layer.   Solder mask is normally used to prevent solder bridging and protect the copper surface. But in high-frequency applications, it can actually become a source of interference. The dielectric constant and loss factor of solder mask differ from those of the base laminate, which can alter the impedance of microstrip lines, especially at frequencies above 10GHz. Removing the solder mask means a purer signal path and better consistency.   The absence of silkscreen is equally straightforward. Without a solder mask, silkscreen adhesion becomes problematic anyway. And on an antenna board, silkscreen provides no benefit for assembly, so omitting it is an easy decision.   This is a classic case of prioritizing function over form — the board does not need to look pretty as long as the electrical performance meets the requirements.     Why Choose WL-CT440? WL-CT440 is Wangling's organic polymer ceramic fiberglass cloth-covered copper clad laminate. It belongs to the thermosetting resin family. The dielectric layer consists of hydrocarbon resin, ceramics, and fiberglass cloth.   At 10GHz and 23°C, it offers a dielectric constant (Dk) of 4.1 and a dissipation factor (Df) of 0.004. What do these numbers mean? Low loss with a moderate dielectric constant — a very good fit for microwave and antenna applications.   But the most appealing feature of WL-CT440 is not its electrical performance alone. It is the full compatibility with FR-4 manufacturing processes. Anyone who has worked with PTFE materials knows that PTFE requires special hole preparation treatments such as plasma etching or sodium naphthalene treatment. Without these, the adhesion of plated copper inside the hole will be insufficient. WL-CT440, on the other hand, can be processed using the conventional workflow of any standard PCB factory — drilling, desmear, electroless copper deposition, pattern transfer — all in one seamless flow. For small-volume prototyping and cost control, this is a real advantage.   Thermal and Mechanical Reliability WL-CT440 has a glass transition temperature (Tg) exceeding 280°C, far above that of standard FR-4. A high Tg means the material will not soften or deform easily under high-temperature operating conditions.   Regarding the coefficient of thermal expansion (CTE), the X-axis is 14ppm/°C and the Y-axis is 18ppm/°C — both matching reasonably well with copper, which sits at approximately 17ppm/°C. The Z-axis CTE is 35ppm/°C. For a two-layer board without blind vias, the thermal reliability stress on vias is relatively low to begin with.   Thermal conductivity is rated at 0.66 W/m·K, which is significantly higher than that of FR-4 at roughly 0.25 W/m·K. This helps with power handling. Moisture absorption is 0.12 percent, which falls within an acceptable range. However, a word of caution is needed here: this board has no solder mask. If used in humid environments, the exposed copper surfaces may face corrosion risks. This needs to be carefully evaluated for the intended application scenario.   One Parameter Worth Special Attention: TCDK WL-CT440 offers a temperature coefficient of dielectric constant (TCDK) of -21 ppm/°C. What does this number tell us? For every 1°C increase in temperature, the dielectric constant decreases by 21 parts per million.   For antenna design, TCDK is a critical parameter. If the Dk of a material varies significantly with temperature, the operating frequency of the antenna will drift — summer measurements will differ from winter measurements, and daytime performance may differ from nighttime performance. The TCDK value of WL-CT440 is quite good, ensuring consistent antenna performance across the full temperature range.   Typical Applications According to the manufacturer, WL-CT440 is primarily used in the following fields:   Aerospace equipment, cabin electronics, and aircraft systems. Microwave antennas and phase-sensitive antennas. Early warning radar and airborne radar systems. Phased array antennas and beam-forming networks. Satellite communication and navigation equipment. Power amplifiers.   Manufacturing Process and Quality Standards The supplied artwork format is Gerber RS-274-X, which can be processed by PCB factories worldwide. The quality standard is IPC-Class-2. Surface finish is immersion gold (ENIG). With no solder mask present, immersion gold effectively protects the copper surface from oxidation while providing good solderability.   A Few Points to Keep in Mind This board design has several aspects that require special attention. First, the absence of a solder mask means the copper surfaces are completely exposed. Despite the immersion gold protection, care must be taken to avoid scratches and contamination during assembly, testing, and use.   Second, there is no silkscreen. Component placement cannot rely on silkscreen reference marks. You will need to depend on the pick-and-place machine's coordinate files or assembly fixtures for manual assembly.   Third, with two layers, 31 vias, and only 2 nets, this topology suggests some form of antenna array or power division network. Special attention should be paid to the impact of vias on the RF path, particularly the continuity of the signal return path.   Final Thoughts The design philosophy behind this two-layer WL-CT440 board is very clear: use a material that can be processed with conventional manufacturing techniques, remove the non-essential solder mask and silkscreen layers, and allocate the cost savings toward performance and reliability.   If you are developing antennas, radar front-ends, or satellite communication modules, and you wish to avoid the processing headaches associated with PTFE materials, WL-CT440 is worth serious consideration. Of course, the protection issues that come with removing the solder mask, the uniformity control of the immersion gold surface, and the calibration of impedance calculations are all details that need to be discussed with your PCB fabricator before prototyping.   Have you run into any challenges when designing high-frequency boards like this one? Feel free to share your experience.

If you're searching for a PCB material that balances low-loss performance with cost-effectiveness, Rogers RO4533 deserves your attention. Today, I want to walk you through a 2-layer rigid PCB design based on RO4533 – a solution that carefully considers material selection, board construction, and manufacturing processes.   Overview: Simple Yet Efficient 2-Layer Structure This PCB measures 123.5mm by 46mm and uses a two-layer construction. The finished board thickness is 0.6mm, with 1oz or 35μm of finished copper weight on the outer layers. The minimum trace and space dimensions are 4 and 5 mils respectively, while the smallest hole size is 0.25mm. There are no blind vias in this design. Every board undergoes 100% electrical testing before shipment to ensure functional integrity.   Looking at the PCB statistics, the board contains 36 components in total. There are 28 pads, consisting of 18 thru-hole pads and 10 surface mount pads all located on the top layer – no SMT pads are placed on the bottom layer. The design includes 17 vias and just 2 nets. The structure isn't overly complex, but every detail is tailored for antenna-class applications.   Why RO4533? RO4533 is Rogers' ceramic-filled, glass-reinforced hydrocarbon-based material. Its biggest advantage over traditional PTFE-based laminates is full compatibility with standard FR-4 fabrication processes. What does this mean in practice? You can process RO4533 using conventional PCB manufacturing techniques – no special hole preparation is required for PTFE materials. For volume production and cost control, this is a very practical benefit.   On the electrical side, RO4533 offers a dielectric constant of 3.3 at 10GHz and a dissipation factor of 0.0025 at the same frequency. Low loss, low dielectric constant, and low passive intermodulation or PIM response make this material highly suitable for microstrip antenna applications – think cellular infrastructure base station antennas, WiMAX antenna networks, and similar wireless communication systems.   Thermal and Mechanical Reliability: Vias You Can Count On RO4533 has a glass transition temperature or Tg exceeding 280°C – well above the 130 to 170°C range of standard FR-4. A high Tg means the material maintains dimensional stability under high temperatures. Combined with a low Z-axis coefficient of thermal expansion or CTE of 37ppm per °C, plated through-hole reliability improves significantly during thermal cycling.   Two additional CTE values are worth noting. The X-axis CTE is 13ppm per °C, while the Y-axis CTE is 11ppm per °C. These match closely with copper, which sits at approximately 17ppm per °C. This good CTE match substantially reduces stress between the copper layers and the dielectric material during temperature changes, helping the antenna board resist warping and deformation.   Thermal Management and Environmental Stability Thermal conductivity is rated at 0.6 watts per meter per Kelvin – mid-to-upper range for RF materials. For antenna designs with meaningful power handling requirements, this parameter makes a real difference.   Moisture absorption is just 0.02 percent. Performance drift in humid environments is minimal, making this material well-suited for outdoor base station equipment.   Surface Finish and Manufacturing Quality Surface finish is Immersion Gold, also known as ENIG, offering good solderability and wire-bonding capability. The top silkscreen is white, while there is no silkscreen on the bottom layer. The top solder mask is green, and again, there is no solder mask on the bottom layer. This asymmetric mask and silkscreen arrangement may be driven by specific antenna radiation requirements or assembly considerations.   Quality standard is IPC-Class-2, which is sufficient for most commercial communication equipment reliability needs. The supplied artwork format is Gerber RS-274-X, which can be processed by PCB factories worldwide.   Key Benefits Let me highlight the key benefits of this design approach. The low loss, low dielectric constant, and low PIM response make this board suitable for a wide range of RF applications. The thermoset resin system is compatible with standard PCB fabrication processes, eliminating the need for specialized handling. Excellent dimensional stability leads to higher yields on larger panel sizes. Uniform mechanical properties help the board maintain its mechanical form during handling. And the high thermal conductivity delivers improved power handling capability.   Typical Applications This PCB design is well-suited for several typical applications. These include cellular infrastructure base station antennas, WiMAX antenna networks, microstrip antenna arrays, and wireless communication infrastructure in general.   Final Thoughts The core idea behind this two-layer RO4533 PCB design is pretty straightforward: use the simplest possible layer count and processes while leveraging RO4533's balanced strengths in RF performance, process compatibility, and reliability.   If you're developing base station antennas, WiMAX network equipment, or other wireless communication products that require low loss and low PIM, this design approach is worth considering. Of course, for your specific project, details like impedance control, antenna feed point layout, and ground via density will need further optimization.   I would love to hear about your experience. In your RF PCB designs, do you lean toward Rogers materials or PTFE-based laminates? What drives your choice – cost, processability, or electrical performance? Feel free to share your thoughts.  

Introduction The F4BTMS series is an upgraded version of the F4BTM series. The material now incorporates a large amount of ceramics and utilizes ultra-thin and ultra-fine fiberglass cloth reinforcement. These enhancements have greatly improved the material's performance, resulting in a wider range of dielectric constants.   The incorporation of ultra-thin, ultra-fine fiberglass cloth reinforcement, along with a precise blend of special nanoceramics and polytetrafluoroethylene resin, minimizes electromagnetic wave interference, reducing dielectric loss and enhancing dimensional stability.   F4BTMS exhibits reduced anisotropy in the X/Y/Z directions, enabling higher frequency usage, increased electrical strength, and improved thermal conductivity.   Features F4BTMS material offers a wide range of dielectric constants, providing flexible options from 2.2 to 10.2, while maintaining a stable value throughout.   Its dielectric loss is extremely low, ranging from 0.0009 to 0.0024, minimizing energy dissipation and improving overall system efficiency.   F4BTMS exhibits excellent temperature coefficient of dielectric constant. The TCDK with a DK value ranging from 2.55 to 10.2, remains within 100 ppm/℃.   The CTE values in the X and Y directions are between 10-50 ppm/°C , while in the Z direction, it is as low as 20-80 ppm/°C. This low thermal expansion ensures exceptional dimensional stability, enabling reliable hole copper connections.   F4BTMS demonstrates remarkable resistance to radiation, retaining stable dielectric and physical properties even after exposure to irradiation; and low outgassing performance, meeting the vacuum outgassing requirements for aerospace applications.   PCB capability We offer a wide range of PCB manufacturing capabilities, allowing you to choose the best options for your needs.   We can accommodate various layer counts, including Single Sided, Double Sided, Multilayer, and Hybrid PCBs.   You can select from different copper weights, such as 1oz (35µm) and 2oz (70µm).   We offer a diverse selection of dielectric thicknesses, ranging from 0.09mm (3.5mil) to 6.35mm (250mil).   Our manufacturing capabilities support PCB sizes up to 400mm X 500mm, catering to designs of different scales.   Various solder mask colors are available, such as Green, Black, Blue, Yellow, Red, and more.   Moreover, we provide diverse surface finish options, including Bare copper, HASL, ENIG, Immersion silver, Immersion tin, OSP, Pure gold and ENEPIG etc.   PCB Material: PTFE,Ultra-thin and ultra-fine fiberglass, ceramics. Designation (F4BTMS ) F4BTMS DK (10GHz) DF (10 GHz) F4BTMS220 2.2±0.02 0.0009 F4BTMS233 2.33±0.03 0.0010 F4BTMS255 2.55±0.04 0.0012 F4BTMS265 2.65±0.04 0.0012 F4BTMS294 2.94±0.04 0.0012 F4BTMS300 3.0±0.04 0.0013 F4BTMS350 3.5±0.05 0.0016 F4BTMS430 4.3±0.09 0.0015 F4BTMS450 4.5±0.09 0.0015 F4BTMS615 6.15±0.12 0.0020 F4BTMS1000 10.2±0.2 0.0020 Layer count: Single Sided, Double Sided PCB, Multilayer PCB, Hybrid PCB Copper weight: 0.5oz (17 µm), 1oz (35µm), 2oz (70µm) Dielectric thickness 0.09mm (3.5mil), 0.127mm (5mil), 0.254mm(10mil),0.508mm(20mil), 0.635mm(25mil), 0.762mm(30mil), 0.787mm(31mil), 1.016mm(40mil), 1.27mm(50mil), 1.5mm(59mil), 1.524mm(60mil), 1.575mm(62mil), 2.03mm(80mil), 2.54mm(100mil), 3.175mm(125mil), 4.6mm(160mil), 5.08mm(200mil), 6.35mm(250mil) PCB size: ≤400mm X 500mm Solder mask: Green, Black, Blue, Yellow, Red etc. Surface finish: Bare copper, HASL, ENIG, Immersion silver, Immersion tin, OSP, Pure gold, ENEPIG etc..   Applications F4BTMS PCBs have extensive applications across various domains, including Aerospace and aviation equipment, Microwave and RF applications, Radar systems, Signal distribution feed networks, Phase-sensitive antennas and phased array antennas etc.

Introduction Wangling’s TP material is a unique high-frequency thermoplastic material in the industry. The dielectric layer of TP-type laminates consists of ceramics and polyphenylene Oxide resin (PPO), without fiberglass reinforcement. The dielectric constant can be precisely adjusted by adjusting the ratio between ceramics and PPO resin. The production process is special, and it has excellent dielectric performance and high reliability. Features The dielectric constant can be arbitrarily selected within the range of 3 to 25 according to circuit requirements, and it is stable. Common dielectric constants include 3.0, 4.4, 6.0, 6.15, 9.2, 9.6, 10.2, 11, 16, and 20. The material demonstrates low dielectric loss, with a slight increase at higher frequencies. However, this increase is not significant within the 10 GHz range. For long-term operation, the material can withstand temperatures ranging from -100°C to +150°C, showcasing excellent low-temperature resistance. It's important to note that temperatures exceeding 180°C may result in deformation, copper foil peeling, and significant changes in electrical performance. The material exhibits radiation resistance and displays low outgassing properties. Furthermore, the adhesion between the copper foil and dielectric is more reliable compared to ceramic substrates with vacuum coating. PCB Capability Let’s see our PCB Capability on TP materials. Layer count: We offer single-sided and double-sided PCBs based on the characteristics of the material. Copper weight: We provide options of 1oz (35µm) and 2oz (70µm), catering to different conductivity requirements. Wide range of dielectric thicknesses are available, such as 0.5mm, 0.8mm, 1.0mm, 1.2mm, 1.5mm, 2.0mm, 3.0mm, 4.0mm, 5.0mm, 6.0mm, 7.0mm, 8.0mm, 10.0mm, and 12.0mm, allowing flexibility in design specifications. Due to laminate size constraints, the maximum PCB we can provide is 150mm X 220mm. Solder mask: We offer various solder mask colors, including green, black, blue, yellow, red, and more, enabling customization and visual distinction. Our surface finish options include bare copper, HASL, ENIG, immersion silver, immersion tin, OSP, pure gold, ENEPIG, and more, ensuring compatibility with your specific requirements. PCB Material: Polyphenylene, ceramic Designation (TP Series) Designation DK DF TP300 3.0±0.06 0.0010 TP440 4.4±0.09 0.0010 TP600 6.0±0.12 0.0010 TP615 6.15±0.12 0.0010 TP920 9.2±0.18 0.0010 TP960 9.6±0.2 0.0011 TP1020 10.2±0.2 0.0011 TP1100 11.0±0.22 0.0011 TP1600 16.0±0.32 0.0015 TP2000 20.0±0.4 0.0020 TP2200 22.0±0.44 0.0022 TP2500 25.0±0.5 0.0025 Layer count: Single Sided, Double Sided PCB Copper weight: 1oz (35µm), 2oz (70µm) Dielectric thickness (or overall thickness) 0.5mm, 0.8mm, 1.0mm, 1.2mm, 1.5mm, 2.0mm, 3.0mm, 4.0mm, 5.0mm, 6.0mm, 7.0mm, 8.0mm, 10.0mm, 12.0mm PCB size: ≤150mm X 220mm Solder mask: Green, Black, Blue, Yellow, Red etc. Surface finish: Bare copper, HASL, ENIG, Immersion silver, Immersion tin, OSP, Pure gold, ENEPIG etc.. Applications Displayed on the screen is a TP high-frequency PCB with a thickness of 1.5mm, featuring OSP coating. TP high-frequency PCBs are also utilized in applications such as Beidou, missile-borne systems, fuzes, and miniaturized antennas etc.

Introduction Wangling’s TF laminates are a composite of microwave and temperature-resistant polytetrafluoroethylene (PTFE) resin material and ceramics. These laminates are free from fiberglass cloth and the dielectric constant is precisely adjusted by adjusting the ratio between ceramics and PTFE resin. With the application of special production processes, they demonstrate outstanding dielectric performance and offer a high level of reliability. Features TF laminates exhibit a stable and wide range of dielectric constant, which ranges from 3 to 16, with common values including 3.0, 6.0, 9.2, 9.6, 10.2, and 16. TF laminates feature exceptionally low dissipation factor, with loss tangent values of 0.0010 for DK ranging from 3.0 to 9.5 at 10GHz, 0.0012 for DK from 9.6 to 11.0 at 10GHz, and 0.0014 for DK spanning 11.1 to 16.0 at 5GHz. With a long-term working temperature surpassing TP materials, they can operate within a wide range of -80°C to +200°C The laminates come in thickness options ranging from 0.635mm to 2.5mm, catering to various design requirements. They boast resistance to radiation and exhibit low outgassing properties. PCB Capability We provide a comprehensive range of PCB manufacturing capabilities to fulfill your specific requirements. At first, we can accommodate both Single Sided and Double Sided PCBs. Then you have the option to select from different copper weights, such as 1oz (35µm) and 2oz (70µm), to meet your conductivity needs. A diverse selection of dielectric thicknesses are available in our house, ranging from 0.635mm to 2.5mm. Our manufacturing capabilities support PCB sizes up to 240mm X 240mm and various solder mask colours like Green, Black, Blue, Yellow, Red, and more. Additionally, we offer various surface finish options, including Bare copper, HASL, ENIG, Immersion silver, Immersion tin, OSP, Pure gold, and ENEPIG etc. PCB Material: Polyphenylene, ceramic Designation (TF Series) Designation DK DF TF300 3.0±0.06 0.0010 TF440 4.4±0.09 0.0010 TF600 6.0±0.12 0.0010 TF615 6.15±0.12 0.0010 TF920 9.2±0.18 0.0010 TF960 9.6±0.19 0.0012 TF1020 10.2±0.2 0.0012 TF1600 16.0±0.4 0.0014 Layer count: Single Sided, Double Sided PCB Copper weight: 1oz (35µm), 2oz (70µm) Dielectric thickness (Dielectric thickness or overall thickness) 0.635mm, 0.8mm, 1.0mm, 1.2mm, 1.5mm, 2.0mm, 2.5mm PCB size: ≤240mm X 240mm Solder mask: Green, Black, Blue, Yellow, Red etc. Surface finish: Bare copper, HASL, ENIG, Immersion silver, Immersion tin, OSP, Pure gold, ENEPIG etc.. Applications TF high-frequency PCBs are utilized in applications of microwave and millimeter-wave domains, such as millimeter-wave radar sensors, antennas, transceivers, modulators, multiplexers, as well as power supply equipment and automatic control equipment.