High Frequency PCB Glossary: RF and Microwave Terms Explained

The copper ring surrounding a drilled hole on each PCB layer. The annular ring ensures electrical continuity between the copper layer and the plated via barrel even after worst-case drill registration offset. IPC Class 2 allows inner layer breakout (ring touching hole edge); IPC Class 3 requires a confirmed minimum ring on every inner layer with no breakout permitted.

The clearance hole in a copper ground plane layer where a signal via passes through without making electrical contact. Anti-pad diameter affects the impedance of the via transition — too small an anti-pad increases parasitic capacitance and shifts via impedance down from the target. Typically sized at approximately 3× the via drill diameter for good impedance continuity at X-band and above.

The ratio of PCB board thickness to via drill diameter. As aspect ratio increases, electroplating solution has increasing difficulty reaching the center of the via barrel, resulting in thin copper plating at the barrel mid-point. Standard limit: 10:1. Advanced limit: 14:1. Exceeding the aspect ratio limit produces unreliable via plating that fails under thermal cycling.

A secondary drilling operation that removes the unused via stub below the signal layer by entering from the back of the board with a slightly larger drill bit. Reduces stub length to a target of ≤10 mil (0.25mm), moving stub resonance above the operating frequency. Required for designs above approximately 10–15 GHz to prevent via stub resonance causing insertion loss notches in the operating band.

A via that starts at an outer PCB layer and terminates at an inner layer — it does not pass all the way through the board. Eliminates the via stub that causes resonance issues in through-hole vias. Each blind via stage requires one additional lamination press cycle. PTFE materials allow maximum 2 press cycles total, limiting PTFE designs to 1 blind via stage.

A specialized bonding film used to join Rogers or PTFE laminate layers together during multilayer PCB lamination. Different bondply types are required for different material combinations. Rogers RO4450F is used for RO4350B and RO4003C hybrid stackups. Rogers 2929 bondply is used for PTFE material hybrids (RO3003, RT5880). Standard FR4 prepreg cannot be used at Rogers material interfaces — it creates impedance discontinuities and unreliable adhesion.

A via that connects two or more inner layers without reaching either outer surface. Not visible from the outside of the finished board. Requires multiple lamination cycles and careful planning within the material's press cycle limit.

The impedance of a transmission line as seen by a traveling wave — determined by the geometry of the trace (width, thickness) and the dielectric material (height, Dk). The standard RF impedance is 50Ω for single-ended circuits and 100Ω differential for differential pairs. When characteristic impedance matches the source and load, maximum power transfer occurs with no reflections. Mismatch causes signal reflections that reduce power transfer and degrade signal integrity.

A transmission line structure where the signal trace is on the outer layer with ground copper pours on the same layer on both sides. Grounded coplanar waveguide (GCPW) adds a ground plane on the adjacent inner layer. CPW is commonly used for RF circuits with surface-mount components and for transitions from PCB trace to connector, as it does not require a reference plane on the adjacent layer.

A PCB manufacturing specification requiring that signal traces are produced to a target characteristic impedance within a specified tolerance (typically ±10% or ±8%). The factory calculates trace width using the confirmed production Dk from the laminate material certificate, then verifies the manufactured result with TDR measurement on a test coupon on every production panel. All high frequency PCB should specify controlled impedance.

The thickness of copper on each PCB layer, expressed in ounces per square foot. Standard values: 0.5 oz (17.5 µm), 1 oz (35 µm), 2 oz (70 µm), 3 oz (105 µm). Copper weight affects trace width for a given impedance target — heavier copper produces a slightly wider trace for the same impedance. Must be specified correctly in the stackup drawing to ensure accurate impedance calculation.

The rate at which a material expands per degree of temperature change, expressed in ppm/°C. Critical for PCB reliability: x-y CTE mismatch between laminate and copper causes trace cracking; z-axis CTE mismatch causes via barrel fatigue under thermal cycling. Rogers RO3003 z-axis CTE: 24 ppm/°C. Rogers RT5880 z-axis CTE: 237 ppm/°C — much higher, limiting RT5880 to low via density designs.

A material property that describes how much electromagnetic energy is absorbed by the dielectric as heat per unit length. Lower Df = less insertion loss. The most important material property for high frequency PCB performance above approximately 5 GHz. Standard FR4 Df ~0.020. Rogers RO4350B Df 0.0037. Rogers RO3003 Df 0.0010. Rogers RT5880 Df 0.0009. At 10 GHz over 6 inches, FR4 adds ~12 dB of insertion loss; RO4350B adds ~2 dB; RO3003 adds ~0.6 dB.

Engineering review of a PCB design before production to identify issues that would prevent manufacturing or cause quality problems. For high frequency PCB, DFM review covers: impedance calculation using confirmed production Dk, bonding film selection, via aspect ratio, annular ring, PTFE process confirmation, lamination cycle count, and material availability. A direct factory performs DFM review internally; a trading company does not.

A material property describing how a dielectric material affects the electric field between conductors. In PCB, Dk determines: signal propagation velocity (lower Dk = faster), trace width for a given impedance (lower Dk = wider trace), and antenna element size (higher Dk = smaller element). Dk must be stable over frequency, temperature, and humidity for consistent RF performance. Rogers RO4350B Dk: 3.48 ±0.05. Rogers RO3003 Dk: 3.00 ±0.04.

A surface finish consisting of electroless nickel, electroless palladium, and immersion gold layers. Eliminates the black pad failure risk associated with ENIG by adding the palladium barrier layer between nickel and gold. Preferred for aerospace and defense IPC Class 3 programs, wire bonding applications, and programs requiring the highest solderability reliability. More expensive than ENIG.

The most common surface finish for high frequency PCB. Consists of electroless nickel (120–300 µin) followed by immersion gold (1–5 µin). Provides flat, solderable surface with good RF performance. The gold layer protects the nickel from oxidation. Risk: black pad (nickel corrosion under the gold layer) — minimized by controlling the ENIG chemistry and process.

Military systems that use the electromagnetic spectrum to detect, intercept, deceive, or deny adversary use of the spectrum. EW PCB typically covers 2–18 GHz instantaneously, requiring materials with stable Dk and minimum Df across the full band — Rogers RT5880 (Dk 2.20, Df 0.0009) is the standard material. IPC Class 3 quality is standard for EW applications.

A brand of PTFE-based high frequency PCB laminates manufactured by Wangling (旺灵), a Chinese material supplier. F4BM220 (Dk 2.20, Df 0.0010) is the most common grade — equivalent in RF performance to Rogers RT5880 at lower cost. Suitable for commercial RF applications where Rogers-certified documentation is not required. All F4B grades require plasma hole wall activation — same PTFE manufacturing process as Rogers PTFE materials.

The most common standard PCB laminate — glass-reinforced epoxy with a flame retardant rating (FR = Flame Retardant, 4 = woven glass reinforced epoxy). Dk approximately 4.0–4.5, Df approximately 0.020 at high frequencies. Suitable for digital circuits and RF circuits below approximately 500 MHz. Too lossy for most RF and microwave applications above 1 GHz. High-Tg FR4 (Tg ≥ 150°C) is recommended for industrial and outdoor applications requiring reliability over wide temperature ranges.

A radar operating mode where the transmitted frequency is continuously swept over a range. FMCW radar measures range by comparing the transmitted and received frequencies. Widely used in automotive radar (77 GHz), industrial level sensing (24 GHz and 77 GHz), and short-range detection systems. The PCB for the radar front-end must support the full sweep bandwidth with consistent impedance.

The standard file format for PCB manufacturing data. Each Gerber file describes one layer of the PCB — copper layers, solder mask layers, silkscreen, and board outline. A complete Gerber set plus NC drill file is the minimum required to manufacture a PCB. For high frequency PCB, a complete stackup drawing with Rogers material grade, dielectric thickness, and copper weight per layer must accompany the Gerber files.

A printed circuit board designed to carry RF and microwave signals above approximately 500 MHz with controlled impedance and minimum insertion loss. Uses specialized laminate materials (Rogers, PTFE, Taconic, F4B) with low Df and stable Dk instead of standard FR4. Always requires controlled impedance specification and TDR verification.

A multilayer PCB stackup combining different laminate materials on different layers — most commonly Rogers or PTFE on RF signal layers and standard FR4 on inner layers. Reduces cost compared to full Rogers construction (typically 30–40% cost saving) while maintaining RF performance where it matters. Requires correct bonding film at the Rogers-FR4 interface: Rogers RO4450F for RO4350B hybrids, Rogers 2929 for PTFE hybrids.

A surface finish depositing 0.15–0.40 µm of silver directly on the copper surface. Provides the lowest surface roughness of common surface finishes — preferred above 10 GHz where surface roughness adds conductor loss (the skin effect confines current to the surface at high frequencies). Silver tarnishes over time; boards should be assembled within shelf life. Not recommended for implantable medical applications due to silver migration risk in biological environments.

The reduction in signal power as it travels through a PCB transmission line, expressed in dB. Composed of conductor loss (resistive loss in copper traces) and dielectric loss (energy absorbed by the PCB laminate). For a receiver system, every dB of insertion loss before the LNA adds directly to the system noise figure. Insertion loss increases with frequency and trace length. Minimized by using low-Df materials (Rogers, PTFE) and maintaining 50Ω controlled impedance.

The standard IPC quality workmanship class for general electronics — commercial and industrial applications. Requires: 20 µm average PTH copper plating, inner layer annular ring breakout permitted, 10% maximum void per hole, electrical test on sampled basis. Suitable for most commercial RF PCB.

The highest standard IPC quality workmanship class for high reliability electronics — aerospace, defense, medical. Requires: 25 µm average PTH copper plating with 20 µm minimum at any point, NO annular ring breakout on any layer, 5% maximum void per hole, 100% electrical test of every board, microsection FAI. Provides significantly better via fatigue reliability under thermal cycling compared to Class 2.

The frequency range from 26.5 GHz to 40 GHz. Ka-band PCB requires PTFE laminate materials — Rogers RO3003 is the standard choice. Standard FR4 and Rogers RO4350B have too much insertion loss at Ka-band for most applications. Ka-band applications include: missile seeker radar, AESA phased array, Ka-band satellite communication, and defense electronic systems. Ka-band PCB manufacturing requires plasma hole wall activation.

The frequency range from 12 GHz to 18 GHz. Common applications: VSAT satellite terminals (10.7–14.5 GHz), Ku-band radar altimeter, point-to-point microwave links. Rogers RO4350B is adequate for many Ku-band designs; Rogers RO4003C (27% lower Df) is preferred for longer feed networks where insertion loss is critical.

The frequency range from 1 GHz to 2 GHz. L-band applications include: GPS (1.176–1.575 GHz), GLONASS, ATC radar, satellite communication uplink. Rogers RO4350B is the standard material for L-band RF PCB. Insertion loss at L-band is low enough that the difference between Rogers and FR4 is often within acceptable margins for short traces.

Alternative name for dissipation factor (Df). See Df.

The most common RF transmission line structure on PCB. The signal trace is on the outer layer, with a continuous ground plane on the adjacent inner layer. Impedance is determined by trace width, copper thickness, dielectric height, and Dk. Microstrip is easy to probe and test. At very high frequencies (above ~20 GHz), the partial air dielectric above the microstrip trace becomes significant in the impedance calculation.

A quality verification method where a PCB sample is cut, polished, and examined under a metallographic microscope to measure copper plating thickness, void percentage, and laminate bond quality. Required for IPC Class 3 First Article Inspection (FAI). Provides objective evidence of via plating quality that electrical testing alone cannot confirm.

The frequency range from approximately 30 GHz to 300 GHz, where the wavelength is in the millimeter range. Includes Ka-band (26.5–40 GHz), V-band (40–75 GHz), and W-band (75–110 GHz). mmWave PCB requires PTFE materials (Rogers RO3003 for Ka-band, Rogers RT5880 for W-band). Standard hydrocarbon materials have too much insertion loss above 26.5 GHz for practical use.

A measure of how much noise a component or system adds to a signal. Expressed in dB. Every dB of insertion loss before the first amplifier (LNA) in a receiver adds 1 dB to the system noise figure. This is why low-loss PCB materials (Rogers, PTFE) are critical for receiver front-end PCB — the material loss directly degrades the system's ability to detect weak signals.

A drilled hole with no copper plating — used for mechanical mounting, tooling holes, and component mechanical clearances. Distinguished from PTH (plated through holes) which carry electrical signals or ground connections.

A flat, rectangular or circular copper element on a PCB substrate that radiates RF energy. The element dimensions are approximately half a wavelength in the substrate material at the operating frequency. Element size scales as 1/√Dk — higher Dk materials produce smaller antenna elements. Rogers RO4350B is most common for patch antennas at L-band through X-band. Rogers RO3003 for Ka-band patches. Rogers RO6010 (Dk 10.2) for maximum size reduction.

A surface treatment process required for PTFE PCB materials before copper plating. RF plasma etches the PTFE hole wall surface at the molecular level, removing fluorine atoms and creating polar functional groups that allow reliable copper adhesion. Without plasma activation, electroless copper deposits with no adhesion to PTFE — the board passes initial testing and fails under thermal cycling. Mandatory for Rogers RO3003, RT5880, Taconic, F4B, and all PTFE-based laminates.

A drilled hole with electroplated copper on the hole wall, creating an electrical connection between all copper layers the hole passes through. PTH copper plating thickness: 20 µm average for IPC Class 2, 25 µm average with 20 µm minimum for IPC Class 3. PTFE materials require plasma activation before PTH plating.

A fluoropolymer used as the base material in high-performance RF PCB laminates. PTFE provides the lowest dielectric loss (Df) of any standard PCB laminate material. Rogers RO3003, RT5880, RO3006, RO6010; Taconic TLY-5, RF-35; and F4B series are all PTFE-based. PTFE is chemically inert — requires plasma or sodium naphthalene hole wall activation before copper plating. Maximum 2 lamination press cycles.

A dimensionless parameter describing how under-damped a resonator or filter is — the ratio of stored energy to energy lost per cycle. Higher Q = sharper resonance, lower insertion loss. PCB material Df directly affects the Q factor of resonant circuits built on that material. Lower Df materials (Rogers RO3003, RT5880) enable higher Q resonators and filters compared to higher Df materials (RO4350B, FR4).

The ratio of reflected signal power to incident signal power at a port, expressed in dB. Return loss indicates how well a transmission line or component is impedance-matched to its source. Higher return loss (in magnitude) = better match. A 50Ω trace with 10% impedance deviation produces approximately -26 dB return loss. A 20% deviation produces approximately -14 dB. Return loss is measured with a VNA or TDR.

The leading manufacturer of high frequency PCB laminates. Rogers materials include: RO4350B and RO4003C (hydrocarbon ceramic, FR4-compatible process) for L-band through Ku-band; RO3003 and RO3003G2 (PTFE ceramic) for Ka-band and 77 GHz; RT5880 and RT5870 (PTFE glass) for wideband EW and W-band; RO3006, RO3010, RO6010 (high Dk PTFE) for compact antenna design.

Rogers PTFE ceramic laminates with Dk 3.0 and Df 0.0010. Standard material for Ka-band (26.5–40 GHz) and 77 GHz automotive radar. RO3003G2 has tighter Dk tolerance (±0.03 vs ±0.04) for high-volume 77 GHz production requiring consistent antenna resonance. Both require PTFE plasma activation and Rogers 2929 bondply for hybrids.

The most widely used high frequency PCB material globally. Rogers hydrocarbon ceramic laminate: Dk 3.48, Df 0.0037, Tg >280°C. Processes on standard FR4-compatible equipment — no plasma activation required. Standard for most RF applications from 500 MHz to 12 GHz including 5G sub-6 GHz, VSAT, S-band and X-band radar, and 24 GHz automotive radar. Rogers RO4450F bondply for hybrid stackups. Maximum 3 lamination cycles.

Rogers PTFE glass laminate with Dk 2.20 (±0.02) and Df 0.0009 — the lowest Df of any standard Rogers material. Dk varies less than 2% from 1 GHz to 110 GHz. Standard material for wideband EW systems covering 2–18 GHz and W-band (75–110 GHz) applications. Requires plasma activation. z-axis CTE of 237 ppm/°C limits use to low via density designs.

The frequency range from 2 GHz to 4 GHz. Common applications: weather radar, air traffic control radar, maritime radar, satellite communication. Rogers RO4350B is the standard material for S-band RF PCB.

A set of parameters describing how RF signals behave at the ports of a network. S11 = reflection at port 1 (return loss). S21 = transmission from port 1 to port 2 (insertion loss or gain). S12 = reverse transmission. S22 = reflection at port 2. Measured with a Vector Network Analyzer (VNA). S-parameters are the primary tool for characterizing RF PCB transmission line performance.

At high frequencies, current flows predominantly in a thin layer on the outer surface of a conductor — the skin depth decreases as frequency increases. At 10 GHz in copper, the skin depth is approximately 0.66 µm. This means conductor loss increases with frequency, and surface roughness becomes more important — rougher copper surfaces increase conductor loss. Immersion silver surface finish has the lowest surface roughness among common PCB finishes, making it preferred above 10 GHz.

The complete layer-by-layer specification of a multilayer PCB — the sequence of copper layers, dielectric materials, and bonding films. For high frequency PCB, every layer must specify: Rogers material grade (not just "Rogers"), dielectric thickness in mm, copper weight in oz, and bonding film type for hybrid stackups. The stackup drawing is the most critical document for high frequency PCB manufacturing — without it, impedance cannot be calculated and the order cannot be confirmed.

A transmission line structure where the signal trace is embedded between two ground planes inside the PCB stackup — completely surrounded by dielectric material. Stripline is shielded from external interference and produces less radiation than microstrip. Impedance is determined by trace width, copper thickness, dielectric height between the ground planes, and Dk. Slightly higher Df than microstrip due to full dielectric embedding.

A manufacturer of PTFE-based high frequency PCB laminates, now part of AGC Group. Key grades: TLY-5A / TLP-5 / TLY-5 (Dk 2.17–2.22, Df 0.0009) — equivalent to Rogers RT5880; TLY-3 (Dk 2.33, Df 0.0012); RF-35 (Dk 3.5, Df 0.0018); RF-60A (Dk 6.5, Df 0.0038); CER-10 (Dk 10.0, Df 0.0035). All Taconic RF materials are PTFE-based requiring plasma activation.

The industry-standard method for verifying controlled impedance on manufactured PCB. A TDR instrument sends a fast-rise-time step pulse into the impedance trace (via a test coupon on the panel edge) and measures reflected signals versus time. The reflection coefficient at each point along the trace is converted to impedance — a flat line at the target impedance confirms the trace is in tolerance. Performed on every production panel for all high frequency PCB orders.

The temperature at which a polymer transitions from a rigid glassy state to a softer rubbery state. Above Tg, PCB materials expand more rapidly in the z-axis, causing via stress. Standard FR4 Tg: 130°C. High-Tg FR4: ≥150°C. Rogers RO4350B Tg: >280°C. PTFE materials have no practical Tg (>500°C) — they do not undergo glass transition. Higher Tg = better reliability at elevated temperatures.

A conductor structure designed to carry RF and microwave signals with controlled characteristic impedance. At high frequencies, PCB traces must be treated as transmission lines — their impedance, not just their resistance, determines signal behavior. Common PCB transmission line structures: microstrip, stripline, coplanar waveguide (CPW), grounded coplanar waveguide (GCPW).

A plated hole in a multilayer PCB that provides an electrical connection between copper layers. Types: through-hole via (connects all layers), blind via (outer to inner layer only), buried via (inner layers only), back-drilled via (through-hole with stub removed). Vias in RF PCB introduce impedance discontinuities and potentially resonant stubs — proper via design is critical for signal integrity above 5 GHz.

A row or double row of ground vias placed parallel to a microstrip or stripline trace to prevent signal coupling to adjacent circuits and reduce radiation. Via pitch along the fence must be no greater than λ/10 at the highest operating frequency. At 10 GHz in Rogers RO4350B, maximum pitch is approximately 1.6mm. Standard practice for isolation-critical circuits above 10 GHz.

The unused portion of a through-hole via barrel below the signal layer. Acts as an open-ended transmission line stub that resonates at a frequency where its electrical length is a quarter wavelength. At resonance, the stub creates an insertion loss notch in the signal response. Via stubs become problematic above approximately 10–15 GHz and must be removed by back drilling or eliminated by using blind vias.

A laboratory instrument that measures S-parameters of RF and microwave components and networks. Measures both magnitude and phase of S11 (return loss) and S21 (insertion loss/gain) over a frequency range. Used to characterize PCB transmission lines, antennas, filters, and complete RF assemblies. The primary instrument for verifying RF PCB performance after assembly.

A measure of impedance mismatch between a transmission line and its load. VSWR of 1.0:1 = perfect match (no reflection). VSWR of 2.0:1 = approximately -9.5 dB return loss. VSWR of 1.5:1 = approximately -14 dB return loss. High VSWR causes signal power to be reflected back toward the source, reducing efficiency and potentially damaging the source in high-power systems.

The frequency range from 75 GHz to 110 GHz. Rogers RT5880 is the only commercially available standard PCB laminate with acceptable insertion loss at W-band. Applications: W-band sensing and imaging, E-band backhaul (71–86 GHz), W-band defense systems. Requires PTFE plasma activation and 2.5 mil advanced minimum line width manufacturing capability.

Bowing or twisting of a PCB panel or board, typically caused by CTE mismatch between laminate layers or asymmetric stackup construction. IPC standard: ≤0.75% for SMT boards, ≤1.5% for through-hole boards. PTFE + FR4 hybrid stackups using Rogers RT5880 (x-y CTE 31 ppm/°C) with FR4 (14–17 ppm/°C) on large panels require warpage analysis. Rogers RO3003 (x-y CTE 17 ppm/°C) produces less warpage in FR4 hybrids.

The frequency range from 8 GHz to 12 GHz. Common applications: fire control radar, airborne weather radar, ship navigation radar, synthetic aperture radar (SAR), X-band satellite communication. Rogers RO4350B is adequate for many X-band designs; Rogers RO4003C (27% lower Df) is preferred for long feed networks or designs where insertion loss is critical.

A Chinese manufacturer of PTFE-based high frequency PCB laminates. Key grades: ZYF220D (Dk 2.20 ±0.02, Df 0.0009), ZYF265D (Dk 2.65), ZYF300CA-P (Dk 3.00), ZYF350CA (Dk 3.50). Cost-effective alternatives to Rogers and Taconic for commercial applications in the Chinese market. All ZY materials are PTFE-based requiring plasma activation.