[{"data":1,"prerenderedAt":378},["ShallowReactive",2],{"blog-fr4-material-properties-en":3,"header-nav-en":47},{"title":4,"description":5,"date":6,"lastUpdated":6,"category":7,"image":8,"readingTime":9,"wordCount":10,"timeRequired":11,"htmlContent":12,"tags":13,"slug":21,"jsonld":22},"FR4 Material Properties: Dk, Tg, Density, CTE Datasheet","What FR-4 is and its key properties: dielectric constant, Tg, Td, CTE, density and thermal conductivity, plus when to choose high-Tg or low-loss FR-4.","2026-10-09","materials","/assets/img/pcb/fr4/pcb-fr4-pcb-hero.webp",9,1734,"PT9M","\u003Cp>Among the hundreds of laminate formulations recognized across the global electronics supply chain, \u003Cstrong>FR-4\u003C/strong> remains the undisputed standard. From low-cost consumer gadgets to multi-layer industrial automation controllers, more than 80% of all rigid printed circuit boards rely on this composite material.\u003C/p>\n\u003Cp>Yet treating the \u003Cstrong>FR4 material\u003C/strong> as a single generic commodity is one of the most common causes of high-temperature delamination, solder joint fatigue, and signal degradation. Modern FR-4 encompasses a wide family of epoxy resin systems, glass weave architectures, and flame-retardant chemistries with vastly different performance boundaries.\u003C/p>\n\u003Cp>This engineering guide delivers an exhaustive breakdown of \u003Cstrong>FR4 material properties\u003C/strong>, compares datasheet parameters across standard, mid-Tg, and high-Tg grades, and outlines when your stackup requires an upgrade.\u003C/p>\n\u003Ch2 id=\"key-takeaways\" data-anchor-en=\"key-takeaways\">Key takeaways\u003C/h2>\n\u003Cul>\n\u003Cli>\u003Cstrong>What FR-4 means:\u003C/strong> "FR" stands for \u003Cstrong>Flame Retardant\u003C/strong>, and "4" designates woven glass-reinforced epoxy resin adhering to NEMA LI 1-1998 and UL94 V-0 flammability standards.\u003C/li>\n\u003Cli>\u003Cstrong>FR4 dielectric constant (Dk):\u003C/strong> Typically ranges from \u003Cstrong>4.2 to 4.7 at 1 GHz\u003C/strong>, decreasing as signal frequency increases. Dk varies depending on the glass-to-resin ratio (e.g., 7628 heavy glass vs. 1080 light glass).\u003C/li>\n\u003Cli>\u003Cstrong>Thermal thresholds (Tg, Td):\u003C/strong> Standard FR-4 features a glass transition temperature ($T_g$) of $130\\text{–}140^\\circ\\text{C}$, mid-$T_g$ sits at $150^\\circ\\text{C}$, and high-$T_g$ reaches $170\\text{–}180^\\circ\\text{C}$. High-$T_g$ formulations provide essential margins for lead-free reflow ($260^\\circ\\text{C}$).\u003C/li>\n\u003Cli>\u003Cstrong>Coefficient of Thermal Expansion (CTE):\u003C/strong> In the Z-axis (thickness), standard FR-4 expands at approximately $50\\text{–}70\\text{ ppm/}^\\circ\\text{C}$ below $T_g$, jumping to $250\\text{–}300\\text{ ppm/}^\\circ\\text{C}$ above $T_g$.\u003C/li>\n\u003Cli>\u003Cstrong>Mechanical & physical metrics:\u003C/strong> FR-4 has a typical density of \u003Cstrong>$1.85\\text{ g/cm}^3$\u003C/strong>, Young's modulus of \u003Cstrong>22–24 GPa\u003C/strong>, and modest thermal conductivity of \u003Cstrong>$0.25\\text{–}0.35\\text{ W/m}\\cdot\\text{K}$\u003C/strong>.\u003C/li>\n\u003C/ul>\n\u003Cdiv data-component=\"BlogQuickQuoteInline\">\u003C/div>\n\n\u003Ch2 id=\"what-is-fr-4-composition-and-grades\" data-anchor-en=\"what-is-fr-4-composition-and-grades\">What is FR-4? Composition and grades\u003C/h2>\n\u003Cp>The term \u003Cstrong>FR4 pcb material\u003C/strong> defines a composite structure combining two foundational ingredients:\u003C/p>\n\u003Col>\n\u003Cli>\u003Cstrong>Woven fiberglass cloth:\u003C/strong> E-glass yarn woven into standardized fabrics (such as styles 106, 1080, 2116, 3313, and 7628) provides mechanical tensile strength, flexural rigidity, and dimensional stability.\u003C/li>\n\u003Cli>\u003Cstrong>Epoxy resin matrix:\u003C/strong> A thermosetting polymer infused with brominated or halogen-free flame retardants and inorganic ceramic fillers that insulates electrical conductors and bonds copper foil.\u003C/li>\n\u003C/ol>\n\u003Cp>Because glass has a high dielectric constant ($Dk \\approx 6.0$) and low CTE, while pure cured epoxy has a lower Dk ($Dk \\approx 3.2$) and high CTE, the exact ratio of resin-to-glass dictates the mechanical and electrical properties of every specific prepreg and core laminate layer.\u003C/p>\n\u003Ch3 id=\"common-fr-4-grades-in-industry\" data-anchor-en=\"common-fr-4-grades-in-industry\">Common FR-4 grades in industry\u003C/h3>\n\u003Cul>\n\u003Cli>\u003Cstrong>Standard Tg FR-4 ($T_g \\approx 135^\\circ\\text{C}$):\u003C/strong> Traditional formulations for tin-lead (SnPb) wave and mild single-pass reflow. Not recommended for modern lead-free cycles.\u003C/li>\n\u003Cli>\u003Cstrong>Mid-Tg FR-4 ($T_g \\approx 150^\\circ\\text{C}$):\u003C/strong> The modern entry-level workhorse (e.g., Kingboard KB-6160), fully compatible with RoHS lead-free soldering on 2 to 6 layer boards.\u003C/li>\n\u003Cli>\u003Cstrong>High-Tg FR-4 ($T_g \\ge 170^\\circ\\text{C}$):\u003C/strong> Formulations (e.g., Shengyi S1000-2, Isola 370HR) engineered for high-layer counts (8+ layers), thick copper, and repeated thermal cycling.\u003C/li>\n\u003Cli>\u003Cstrong>Halogen-Free FR-4:\u003C/strong> Replaces bromine with phosphorus compounds, reducing toxic emissions in consumer portable and green certifications.\u003C/li>\n\u003C/ul>\n\u003Ch2 id=\"fr4-material-properties-datasheet-at-a-glance\" data-anchor-en=\"fr4-material-properties-datasheet-at-a-glance\">FR4 material properties datasheet at a glance\u003C/h2>\n\u003Cp>The following engineering datasheet table summarizes the critical electrical, thermal, and mechanical parameters of verified \u003Cstrong>pcb fr4 material\u003C/strong> grades tested under IPC-TM-650 methods:\u003C/p>\n\u003Ctable>\n\u003Cthead>\n\u003Ctr>\n\u003Cth>Property\u003C/th>\n\u003Cth>Test Method / Condition\u003C/th>\n\u003Cth align=\"right\">Standard FR-4 (Tg 135)\u003C/th>\n\u003Cth align=\"right\">Mid-Tg FR-4 (Tg 150)\u003C/th>\n\u003Cth align=\"right\">High-Tg FR-4 (Tg 170+)\u003C/th>\n\u003Cth>Units\u003C/th>\n\u003C/tr>\n\u003C/thead>\n\u003Ctbody>\u003Ctr>\n\u003Ctd>\u003Cstrong>Glass Transition Temp ($T_g$)\u003C/strong>\u003C/td>\n\u003Ctd>DSC / TMA\u003C/td>\n\u003Ctd align=\"right\">135\u003C/td>\n\u003Ctd align=\"right\">150\u003C/td>\n\u003Ctd align=\"right\">170–180\u003C/td>\n\u003Ctd>$^\\circ\\text{C}$\u003C/td>\n\u003C/tr>\n\u003Ctr>\n\u003Ctd>\u003Cstrong>Decomposition Temp ($T_d$)\u003C/strong>\u003C/td>\n\u003Ctd>TGA (5% weight loss)\u003C/td>\n\u003Ctd align=\"right\">305\u003C/td>\n\u003Ctd align=\"right\">320\u003C/td>\n\u003Ctd align=\"right\">340–350\u003C/td>\n\u003Ctd>$^\\circ\\text{C}$\u003C/td>\n\u003C/tr>\n\u003Ctr>\n\u003Ctd>\u003Cstrong>Time to Delamination (T260)\u003C/strong>\u003C/td>\n\u003Ctd>TMA\u003C/td>\n\u003Ctd align=\"right\">5–10\u003C/td>\n\u003Ctd align=\"right\">15–20\u003C/td>\n\u003Ctd align=\"right\">> 30–60\u003C/td>\n\u003Ctd>minutes\u003C/td>\n\u003C/tr>\n\u003Ctr>\n\u003Ctd>\u003Cstrong>Time to Delamination (T288)\u003C/strong>\u003C/td>\n\u003Ctd>TMA\u003C/td>\n\u003Ctd align=\"right\">0–2\u003C/td>\n\u003Ctd align=\"right\">2–5\u003C/td>\n\u003Ctd align=\"right\">10–15\u003C/td>\n\u003Ctd>minutes\u003C/td>\n\u003C/tr>\n\u003Ctr>\n\u003Ctd>\u003Cstrong>Dielectric Constant (Dk @ 1 GHz)\u003C/strong>\u003C/td>\n\u003Ctd>IPC-TM-650 2.5.5.9\u003C/td>\n\u003Ctd align=\"right\">4.40–4.60\u003C/td>\n\u003Ctd align=\"right\">4.30–4.45\u003C/td>\n\u003Ctd align=\"right\">4.10–4.35\u003C/td>\n\u003Ctd>— (dimensionless)\u003C/td>\n\u003C/tr>\n\u003Ctr>\n\u003Ctd>\u003Cstrong>Dielectric Constant (Dk @ 10 GHz)\u003C/strong>\u003C/td>\n\u003Ctd>IPC-TM-650 2.5.5.5\u003C/td>\n\u003Ctd align=\"right\">4.10–4.30\u003C/td>\n\u003Ctd align=\"right\">4.05–4.20\u003C/td>\n\u003Ctd align=\"right\">3.90–4.10\u003C/td>\n\u003Ctd>— (dimensionless)\u003C/td>\n\u003C/tr>\n\u003Ctr>\n\u003Ctd>\u003Cstrong>Dissipation Factor (Df @ 1 GHz)\u003C/strong>\u003C/td>\n\u003Ctd>IPC-TM-650 2.5.5.9\u003C/td>\n\u003Ctd align=\"right\">0.020\u003C/td>\n\u003Ctd align=\"right\">0.016\u003C/td>\n\u003Ctd align=\"right\">0.012–0.015\u003C/td>\n\u003Ctd>—\u003C/td>\n\u003C/tr>\n\u003Ctr>\n\u003Ctd>\u003Cstrong>Dissipation Factor (Df @ 10 GHz)\u003C/strong>\u003C/td>\n\u003Ctd>IPC-TM-650 2.5.5.5\u003C/td>\n\u003Ctd align=\"right\">0.025\u003C/td>\n\u003Ctd align=\"right\">0.020\u003C/td>\n\u003Ctd align=\"right\">0.015–0.018\u003C/td>\n\u003Ctd>—\u003C/td>\n\u003C/tr>\n\u003Ctr>\n\u003Ctd>\u003Cstrong>Z-Axis CTE (Below $T_g$)\u003C/strong>\u003C/td>\n\u003Ctd>TMA ($30\\text{–}130^\\circ\\text{C}$)\u003C/td>\n\u003Ctd align=\"right\">60–75\u003C/td>\n\u003Ctd align=\"right\">50–65\u003C/td>\n\u003Ctd align=\"right\">40–50\u003C/td>\n\u003Ctd>$\\text{ppm/}^\\circ\\text{C}$\u003C/td>\n\u003C/tr>\n\u003Ctr>\n\u003Ctd>\u003Cstrong>Z-Axis CTE (Above $T_g$)\u003C/strong>\u003C/td>\n\u003Ctd>TMA ($> T_g$)\u003C/td>\n\u003Ctd align=\"right\">280–320\u003C/td>\n\u003Ctd align=\"right\">250–290\u003C/td>\n\u003Ctd align=\"right\">200–240\u003C/td>\n\u003Ctd>$\\text{ppm/}^\\circ\\text{C}$\u003C/td>\n\u003C/tr>\n\u003Ctr>\n\u003Ctd>\u003Cstrong>Total Z-Axis Expansion ($50\\text{–}260^\\circ\\text{C}$)\u003C/strong>\u003C/td>\n\u003Ctd>TMA\u003C/td>\n\u003Ctd align=\"right\">4.5–5.5%\u003C/td>\n\u003Ctd align=\"right\">3.5–4.2%\u003C/td>\n\u003Ctd align=\"right\">2.5–3.0%\u003C/td>\n\u003Ctd>% expansion\u003C/td>\n\u003C/tr>\n\u003Ctr>\n\u003Ctd>\u003Cstrong>X/Y-Axis CTE\u003C/strong>\u003C/td>\n\u003Ctd>TMA\u003C/td>\n\u003Ctd align=\"right\">14–17\u003C/td>\n\u003Ctd align=\"right\">13–16\u003C/td>\n\u003Ctd align=\"right\">12–15\u003C/td>\n\u003Ctd>$\\text{ppm/}^\\circ\\text{C}$\u003C/td>\n\u003C/tr>\n\u003Ctr>\n\u003Ctd>\u003Cstrong>Thermal Conductivity ($k$)\u003C/strong>\u003C/td>\n\u003Ctd>Hot-wire / Flash\u003C/td>\n\u003Ctd align=\"right\">0.25\u003C/td>\n\u003Ctd align=\"right\">0.30\u003C/td>\n\u003Ctd align=\"right\">0.35–0.40\u003C/td>\n\u003Ctd>$\\text{W/m}\\cdot\\text{K}$\u003C/td>\n\u003C/tr>\n\u003Ctr>\n\u003Ctd>\u003Cstrong>Density ($\\rho$)\u003C/strong>\u003C/td>\n\u003Ctd>ASTM D792\u003C/td>\n\u003Ctd align=\"right\">1.85\u003C/td>\n\u003Ctd align=\"right\">1.85\u003C/td>\n\u003Ctd align=\"right\">1.85–1.90\u003C/td>\n\u003Ctd>$\\text{g/cm}^3$\u003C/td>\n\u003C/tr>\n\u003Ctr>\n\u003Ctd>\u003Cstrong>Young's Modulus ($E$)\u003C/strong>\u003C/td>\n\u003Ctd>ASTM D638\u003C/td>\n\u003Ctd align=\"right\">22\u003C/td>\n\u003Ctd align=\"right\">23\u003C/td>\n\u003Ctd align=\"right\">24–26\u003C/td>\n\u003Ctd>$\\text{GPa}$\u003C/td>\n\u003C/tr>\n\u003Ctr>\n\u003Ctd>\u003Cstrong>Poisson's Ratio ($\\nu$)\u003C/strong>\u003C/td>\n\u003Ctd>Static tension\u003C/td>\n\u003Ctd align=\"right\">0.14\u003C/td>\n\u003Ctd align=\"right\">0.14\u003C/td>\n\u003Ctd align=\"right\">0.14\u003C/td>\n\u003Ctd>—\u003C/td>\n\u003C/tr>\n\u003Ctr>\n\u003Ctd>\u003Cstrong>Dielectric Breakdown Voltage\u003C/strong>\u003C/td>\n\u003Ctd>IPC-TM-650 2.5.6\u003C/td>\n\u003Ctd align=\"right\">> 40\u003C/td>\n\u003Ctd align=\"right\">> 45\u003C/td>\n\u003Ctd align=\"right\">> 50\u003C/td>\n\u003Ctd>$\\text{kV/mm}$\u003C/td>\n\u003C/tr>\n\u003Ctr>\n\u003Ctd>\u003Cstrong>Water Absorption\u003C/strong>\u003C/td>\n\u003Ctd>24h immersion @ $23^\\circ\\text{C}$\u003C/td>\n\u003Ctd align=\"right\">0.20%\u003C/td>\n\u003Ctd align=\"right\">0.15%\u003C/td>\n\u003Ctd align=\"right\">0.10%\u003C/td>\n\u003Ctd>% weight\u003C/td>\n\u003C/tr>\n\u003C/tbody>\u003C/table>\n\u003Ch2 id=\"electrical-performance-fr4-dielectric-constant-and-loss\" data-anchor-en=\"electrical-performance-fr4-dielectric-constant-and-loss\">Electrical performance: FR4 dielectric constant and loss\u003C/h2>\n\u003Cp>Understanding the \u003Ca href=\"/en/blog/what-is-dielectric-constant\">dielectric constant\u003C/a> of FR-4 is vital for controlled impedance routing:\u003C/p>\n\u003Ch3 id=\"1-dk-variations-by-glass-style\" data-anchor-en=\"1-dk-variations-by-glass-style\">1. Dk variations by glass style\u003C/h3>\n\u003Cp>Lightweight prepregs with high resin content (such as style 106, ~75% resin) exhibit a lower Dk ($Dk \\approx 3.8\\text{–}4.0$). Conversely, heavy core laminates with tight glass weaves (such as style 7628, ~43% resin) display a significantly higher Dk ($Dk \\approx 4.6\\text{–}4.7$). Circuit designers must always calculate trace impedance using the specific prepreg/core stackup approved by the PCB manufacturer, rather than assuming an arbitrary average of 4.5.\u003C/p>\n\u003Ch3 id=\"2-high-frequency-attenuation\" data-anchor-en=\"2-high-frequency-attenuation\">2. High-frequency attenuation\u003C/h3>\n\u003Cp>With a dissipation factor ($\\text{Df} \\approx 0.015\\text{–}0.020$), standard FR-4 dissipates significant signal energy into dielectric heating above 3–5 GHz. For PCIe 4.0/5.0, 10G+ Ethernet, or RF microwave designs, upgrading to low-loss mid-Dk materials (such as Panasonic Megtron 6 or Rogers RO4350B) prevents excessive eye-diagram closure.\u003C/p>\n\u003Ch2 id=\"thermal-properties-tg-td-and-cte\" data-anchor-en=\"thermal-properties-tg-td-and-cte\">Thermal properties: Tg, Td, and CTE\u003C/h2>\n\u003Cp>Reliability failures during lead-free assembly and thermal cycling trace back to three thermal properties:\u003C/p>\n\u003Ch3 id=\"glass-transition-temperature-tg\" data-anchor-en=\"glass-transition-temperature-tg\">Glass Transition Temperature ($T_g$)\u003C/h3>\n\u003Cp>The \u003Ca href=\"/en/blog/glass-transition-temperature-tg\">glass transition temperature\u003C/a> marks the temperature where the cured polymer chains transition from a rigid glassy state into a softer rubbery state. Below $T_g$, the material expands modestly. Once temperature exceeds $T_g$, expansion accelerates by 400% to 500%.\u003C/p>\n\u003Ch3 id=\"z-axis-cte-and-pth-barrel-reliability\" data-anchor-en=\"z-axis-cte-and-pth-barrel-reliability\">Z-Axis CTE and PTH barrel reliability\u003C/h3>\n\u003Cp>Copper has a CTE of $17 \\text{ ppm/}^\\circ\\text{C}$. In the planar X and Y directions, FR-4's woven glass fibers restrain expansion to $12\\text{–}16 \\text{ ppm/}^\\circ\\text{C}$, closely matching copper. However, along the vertical Z-axis, there are no glass fibers to restrain expansion.\u003C/p>\n\u003Cp>During $260^\\circ\\text{C}$ lead-free reflow, standard FR-4 expands vertically by 4.5% to 5.5%, whereas copper foil expands by less than 0.5%. This severe mechanical mismatch places immense tensile strain on plated through-hole (PTH) barrels, leading to barrel cracking, corner knee fractures, and inner-layer via separation. Specifying high-Tg FR-4 suppresses total Z-expansion below 3.0%, ensuring survivability across multiple thermal shock cycles.\u003C/p>\n\u003Ch3 id=\"decomposition-temperature-td\" data-anchor-en=\"decomposition-temperature-td\">Decomposition Temperature ($T_d$)\u003C/h3>\n\u003Cp>$T_d$ represents the point where the polymer chemically breaks down and loses 5% of its original mass. Standard FR-4 begins irreversible degradation around $305^\\circ\\text{C}$, whereas high-reliability formulations reach $340\\text{–}350^\\circ\\text{C}$, providing safe process windows during manual soldering rework.\u003C/p>\n\u003Ch2 id=\"mechanical-characteristics-density-young39s-modulus-and-stiffness\" data-anchor-en=\"mechanical-characteristics-density-youngs-modulus-and-stiffness\">Mechanical characteristics: Density, Young's modulus, and stiffness\u003C/h2>\n\u003Cul>\n\u003Cli>\u003Cstrong>FR4 density:\u003C/strong> Measures approximately \u003Cstrong>$1.85\\text{ g/cm}^3$\u003C/strong> (or $0.067\\text{ lb/in}^3$). For weight-sensitive aerospace avionics or handheld drones, multilayer FR-4 weight can be predicted directly from board volume and copper ounce weights.\u003C/li>\n\u003Cli>\u003Cstrong>Flexural strength & Young's Modulus:\u003C/strong> With an elastic modulus of $22\\text{–}26\\text{ GPa}$, FR-4 delivers exceptional stiffness that resists board sagging under heavy transformers and inductors.\u003C/li>\n\u003Cli>\u003Cstrong>Thermal conductivity:\u003C/strong> Standard FR-4 is a thermal insulator ($k \\approx 0.3 \\text{ W/m}\\cdot\\text{K}$). High-power LED arrays and motor drive stages require thermal vias, heavy copper planes, or transition to aluminum metal-core PCBs (MCPCBs) to shed heat.\u003C/li>\n\u003C/ul>\n\u003Ch2 id=\"when-is-fr-4-not-enough\" data-anchor-en=\"when-is-fr-4-not-enough\">When is FR-4 not enough?\u003C/h2>\n\u003Cp>While \u003Ca href=\"/en/pcb/fr4-pcb\">FR4 PCB manufacturing\u003C/a> accommodates the vast majority of applications, designers must move beyond standard FR-4 when:\u003C/p>\n\u003Col>\n\u003Cli>\u003Cstrong>Layer count exceeds 8–10 layers:\u003C/strong> Total Z-axis expansion strains high-aspect-ratio vias during lead-free soldering. Upgrade to high-Tg FR-4 ($T_g \\ge 170^\\circ\\text{C}$, IPC-4101/126).\u003C/li>\n\u003Cli>\u003Cstrong>Signal speeds exceed 10 Gbps:\u003C/strong> High Df causes severe channel insertion loss. Migrate to mid-loss or ultra-low-loss laminates (e.g., Megtron 6).\u003C/li>\n\u003Cli>\u003Cstrong>Continuous operating temperature exceeds $130^\\circ\\text{C}$:\u003C/strong> Under-hood automotive and downhole oil-and-gas electronics demand polyimide substrates ($T_g > 250^\\circ\\text{C}$).\u003C/li>\n\u003Cli>\u003Cstrong>RF/Microwave frequencies exceed 3 GHz:\u003C/strong> Antennas and phased arrays demand tightly controlled Dk tolerances ($\\pm 0.05$) found only in hydrocarbon/ceramic or PTFE laminates.\u003C/li>\n\u003C/ol>\n\u003Ch2 id=\"calling-out-fr-4-in-an-rfq-fabrication-drawing\" data-anchor-en=\"calling-out-fr-4-in-an-rfq-fabrication-drawing\">Calling out FR-4 in an RFQ / Fabrication Drawing\u003C/h2>\n\u003Cp>Avoid writing vague notes like "Material: FR-4" on your fabrication print. To ensure reproducible quality from board houses:\u003C/p>\n\u003Cul>\n\u003Cli>\u003Cstrong>Specify IPC-4101 slash sheets:\u003C/strong> Call out \u003Ccode>IPC-4101/126\u003C/code> for High-Tg lead-free FR-4, or \u003Ccode>IPC-4101/21\u003C/code> for standard mid-Tg FR-4.\u003C/li>\n\u003Cli>\u003Cstrong>State thermal limits:\u003C/strong> Explicitly mandate \u003Ccode>$T_g \\ge 170^\\circ\\text{C}$, $T_d \\ge 340^\\circ\\text{C}$, and $T288 \\ge 10\\text{ min}$\u003C/code>.\u003C/li>\n\u003Cli>\u003Cstrong>Specify UL 94 V-0 flammability:\u003C/strong> Ensure the fabricator applies an authorized UL marking with recognized CTI ratings (Comparative Tracking Index > 175 V or PLC 3).\u003C/li>\n\u003C/ul>\n\u003Chr>\n\u003Ch2 id=\"faq\">Frequently Asked Questions\u003C/h2>\n\n\u003Cp>\u003Cstrong>Q: What is the dielectric constant of FR4 material?\u003C/strong>\nA: The dielectric constant (Dk) of FR4 material typically ranges between 4.2 and 4.7 at 1 GHz. Because FR-4 is a composite of glass and epoxy resin, the exact Dk depends on the glass weave style, resin percentage, and signal frequency.\u003C/p>\n\u003Cp>\u003Cstrong>Q: What is the difference between FR-4 Tg 150 and Tg 170?\u003C/strong>\nA: FR-4 Tg 150 is a mid-Tg formulation designed for standard 2 to 6 layer lead-free boards. FR-4 Tg 170 is a high-Tg material engineered with greater cross-linking density, delivering lower Z-axis expansion and superior thermal endurance for high-layer count (8+ layer) and automotive applications.\u003C/p>\n\u003Cp>\u003Cstrong>Q: What is the density of FR4?\u003C/strong>\nA: The density of standard FR-4 is approximately $1.85\\text{ g/cm}^3$ ($1850\\text{ kg/m}^3$), which is about 20% lighter than aluminum and significantly lighter than copper ($8.96\\text{ g/cm}^3$).\u003C/p>\n\u003Cp>\u003Cstrong>Q: What is the thermal conductivity of FR-4?\u003C/strong>\nA: FR-4 has poor thermal conductivity, typically between $0.25$ and $0.35\\text{ W/m}\\cdot\\text{K}$. To dissipate heat from power components on FR-4 boards, designers rely on thermal via arrays, thick copper pours (2–3 oz), or external heat sinks.\u003C/p>\n\u003Cp>\u003Cstrong>Q: Is FR4 flame retardant?\u003C/strong>\nA: Yes. The "FR" in FR-4 stands for Flame Retardant. FR-4 laminates are certified to UL94 V-0 flammability, meaning flaming combustion extinguishes within 10 seconds on vertical specimens without dripping flaming particles.\u003C/p>\n\n\u003Csection class=\"related-links\" aria-label=\"Related\">\u003Ch3>Related links\u003C/h3>\u003Cul>\u003Cli>\u003Ca href=\"/en/blog/what-is-dielectric-constant\">dielectric constant\u003C/a>\u003C/li>\u003Cli>\u003Ca href=\"/en/blog/glass-transition-temperature-tg\">glass transition temperature\u003C/a>\u003C/li>\u003Cli>\u003Ca href=\"/en/pcb/fr4-pcb\">FR4 PCB manufacturing\u003C/a>\u003C/li>\u003C/ul>\u003C/section>",[14,15,16,17,18,19,20],"FR4 Material","FR4 Properties","PCB Substrate","FR4 Dielectric Constant","FR4 Tg","Thermal Conductivity","PCB 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