Isola IS580G is a halogen-free 205°C Tg laminate with Td 385°C, Dk 3.80, and Df 0.006 — the highest decomposition temperature in its class. Full technical guide covering complete specs, Z-axis CTE improvement, T288/T300 performance, processing guidelines, and comparison with I-Speed, FR408HR, and TerraGreen 400GE.
Primary keyword: Isola IS580G | ~2,500 words
The brief for Isola IS580G is clear and specific: halogen-free, 205°C Tg, very low loss, and the highest decomposition temperature in its class at 385°C. Introduced in October 2023, it’s one of the newer entries in the Isola portfolio, but it plugs a gap that has been real for a while — there wasn’t a clean halogen-free option that paired FR-4-like processability with both high thermal reliability and a Dk/Df step up from standard epoxy, without paying the price premium of the ultra-low-loss grades like I-Tera MT40 or Tachyon 100G.
IS580G is the material you reach for when the PCB program requires halogen-free compliance, the design involves high-layer-count multilayer construction or HDI, the assembly goes through aggressive lead-free reflow, and the application environment runs warm enough that Tg 180°C FR-4 leaves you uncomfortable. It isn’t trying to compete with the low-Df signal integrity materials — its Df of 0.006 sits alongside I-Speed in the “very low loss vs. standard FR-4” category. What sets it apart is delivering that performance level in a halogen-free, 205°C Tg body with a Td of 385°C that nothing else in its class currently matches.
What Is Isola IS580G and What Problem Does It Solve?
IS580G laminate and prepreg products are manufactured with Isola’s high-performance, low-loss, multi-functional resin system, reinforced with electrical grade (E-glass) glass fabric. The unique resin system delivers a greater than 25% improvement in Z-axis expansion while maintaining good flow and fill properties. These properties, coupled with superior moisture resistance at reflow, result in a halogen-free product with an industry-leading combination of thermal and electrical performance.
The engineering problem being solved is the combination of constraints that have historically been hard to satisfy simultaneously. Halogen-free materials have often carried a Tg penalty compared to brominated alternatives — getting to 200°C+ Tg in a halogen-free formulation without using phosphorus-based flame retardants that increase polarity (and therefore raise Df) is genuinely difficult resin chemistry. IS580G’s multi-functional resin system achieves 205°C DMA Tg (190°C TMA) and Td 385°C in a halogen-free body while holding Dk to 3.80 and Df to 0.006 — the electrical performance tier of Isola’s I-Speed material, the thermal performance tier above FR408HR, and the halogen-free compliance that neither of those materials provides.
IS580G is a halogen-free 205°C Tg resin system for multilayer PWB applications where maximum thermal performance and reliability are required. That’s Isola’s own positioning statement for the material — and it captures the application intent precisely.
Isola IS580G Complete Specifications
The complete property table below is drawn from the official Isola datasheet (Revision B, March 2024), developed using standard test methods per IPC-TM-650 unless otherwise noted.
Full Electrical, Thermal, and Mechanical Properties
| Property | Typical Value | Test Method / Condition |
| Dielectric Constant (Dk) @ 5/10/20 GHz | 3.80 | Bereskin Stripline |
| Dissipation Factor (Df) @ 5/10/20 GHz | 0.006 | Bereskin Stripline |
| Glass Transition Temp (Tg) — DMA | 205°C | IPC-TM-650 2.4.24.4 |
| Glass Transition Temp (Tg) — TMA | 190°C | IPC-TM-650 2.4.24C |
| Decomposition Temp (Td) | 385°C | TGA, 5% wt loss, 2.4.24.6 |
| T288 | >60 minutes | IPC-TM-650 2.4.24.1 |
| T300 | Documented | IPC-TM-650 2.4.24.1 |
| Z-Axis CTE (pre-Tg) | 30 ppm/°C | TMA |
| Z-Axis CTE (post-Tg) | 190 ppm/°C | TMA |
| Z-Axis CTE (50–260°C, total) | 1.8% | TMA |
| X/Y-Axis CTE | 13/14 ppm/°C | TMA |
| Thermal Conductivity | 0.5 W/m·K | ASTM E1952 |
| Thermal Stress, 10 sec @ 288°C | Pass | IPC-TM-650 2.4.13.1 |
| Volume Resistivity | 3×10⁸ MΩ·cm | IPC-TM-650 2.5.17.1 |
| Surface Resistivity | 3.5×10⁸ MΩ | IPC-TM-650 2.5.17.1 |
| Dielectric Breakdown | 70 kV | IPC-TM-650 2.5.6B |
| Arc Resistance | 190 seconds | IPC-TM-650 2.5.1B |
| Electric Strength | 63 (1600) kV/mm (V/mil) | IPC-TM-650 2.5.6.2A |
| Comparative Tracking Index (CTI) | Class 2 (250–499 V) | UL 746A / ASTM D3638 |
| Moisture Absorption | 0.10% | IPC-TM-650 2.6.2.1A |
| Peel Strength (after thermal stress) | 0.75 N/mm (4.3 lb/in) | IPC-TM-650 2.4.8.2A |
| Flexural Strength (lengthwise / crosswise) | 537 / 393 MPa (78 / 57 kpsi) | IPC-TM-650 2.4.4B |
| Young’s Modulus (lengthwise / crosswise) | 25,000 / 23,000 MPa | ASTM D790-15e2 |
| RTI (Relative Thermal Index) | 160°C | UL 746 |
| UL Flammability | V-0 | UL 94 |
| UL File Number | E41625 | |
| IPC Classification | IPC-4101/140 | |
| RoHS | Compliant |
A Note on Tg Measurement Method
Engineers encountering IS580G for the first time sometimes see the 205°C figure (DMA) alongside 190°C (TMA) and wonder which value to use. The DMA method measures the viscoelastic behavior of the cured resin system and typically yields the highest Tg value. TMA measures dimensional change and produces a somewhat lower number. Both are valid for different purposes. For practical design and assembly decisions, Isola’s headline figure of 205°C (DMA) is appropriate for comparing thermal margins across materials. The TMA value of 190°C is what most thermal expansion modeling tools use for stack-up analysis, since it represents the transition in dimensional behavior.
Product Availability and Construction Details
Standard Material Offering
| Parameter | Available Options |
| Laminate thickness | 2 to 30 mil (0.05 to 0.75 mm) |
| Copper foil type | RTF (Reverse Treat Foil) |
| Copper weight | ½, 1, 2 oz (18, 35, 70 µm) |
| Prepreg | Roll or panel form; tooling of panels; moisture barrier packaging |
| Glass fabric | E-glass; square weave glass; mechanically spread glass |
| All IS580G glass | Spread weave in both directions (standard) |
The RTF (Reverse Treat Foil) copper specification is the standard offering for IS580G. RTF has nodules on the bond face of the foil (the face bonded to the dielectric) rather than on the outer surface, which reduces the effective roughness that current encounters at the copper-dielectric interface and provides better adhesion than smooth copper without the full surface roughness of standard HTE foil. For IS580G’s target applications — high-reliability multilayer boards operating at digital data rates where Df 0.006 is appropriate — RTF provides a good balance of adhesion and conductor loss performance.
Performance and Processing Feature Summary
| Category | Attribute |
| Performance | CAF resistant |
| Halogen free | |
| >25% Z-axis CTE improvement | |
| Low moisture absorption (0.10%) | |
| T288: >60 minutes | |
| T300: documented | |
| 6x 288°C solder float capable | |
| Processing | FR-4 process compatible |
| Excellent fill and flow | |
| Multiple lamination cycles | |
| HDI technology compatible | |
| Lead-free compatible | |
| Compliance | UL 94 V-0 (File E41625) |
| IPC-4101/140 | |
| RoHS compliant | |
| Halogen-free |
The Thermal Performance Story: Why Td 385°C and T300 Matter
The Td of 385°C is the headline that separates IS580G from everything else in its peer group. Looking across Isola’s thermal reliability segment: FR408HR has Td 360°C; I-Speed has Td 360°C; IS420 (Isola’s earlier high-Tg option) has Td 330–340°C; and the standard 370HR has Td 340°C. IS580G at Td 385°C is 25°C above the next-best option in its cost tier.
Why does Td matter to PCB engineers? Decomposition temperature is the temperature at which the resin matrix begins irreversible chemical breakdown, losing mass as it outgasses decomposition products. That breakdown mechanism is what causes catastrophic delamination at high temperatures — once the resin starts decomposing, the board cannot recover. For high-reliability programs where the board must survive extended operation at elevated temperature, qualification testing at temperatures closer to Td, or assembly processes that push material limits, a higher Td buys real margin.
The T288 rating of greater than 60 minutes and the documented T300 performance are the practical consequence of that high Td. T260, T288, and T300 measure the time-to-delamination in an isothermal test — how long the material can sit at that temperature before layer separation occurs. T300 is relevant for the most demanding lead-free assembly environments and for automotive-grade qualification packages. IS580G’s T300 documentation is a direct enabler for automotive and industrial programs where T300 appears in the material procurement specification.
The Z-axis total expansion of 1.8% (50–260°C) is equally important for via reliability in high-layer-count designs. Lower Z-axis CTE means less barrel stress on plated through-holes during thermal cycling, which translates directly to longer via lifetime under the Coffin-Manson fatigue model. IS580G’s >25% improvement in Z-axis expansion versus competing halogen-free materials is the spec that makes it viable for thick, high-layer-count PCBs where halogen-free options have previously been limited.
IS580G vs Comparable Materials: Where It Fits in the Landscape
Isola IS580G in Context: Key Competitor Comparison
| Material | Manufacturer | Tg (DMA) | Td | Dk (10 GHz) | Df (10 GHz) | Halogen-Free |
| IS580G | Isola | 205°C | 385°C | 3.80 | 0.006 | Yes |
| I-Speed | Isola | 180°C | 360°C | 3.63 | 0.006 | No |
| FR408HR | Isola | 190°C | 360°C | 3.68 | 0.0092 | No |
| 370HR | Isola | 180°C | 340°C | 4.04 | 0.021 | No |
| IS550H | Isola | ~200°C | 400°C | 4.43 | 0.016 | Yes |
| I-Tera MT40 | Isola | 215°C | 360°C | 3.45 | 0.0031 | No |
| TerraGreen 400GE | Isola | 200°C | 380°C | 3.29 | 0.0026 | Yes |
The comparison with I-Speed is the most instructive for the “very low loss” electrical tier. Both materials carry Df 0.006. IS580G has a 25°C higher DMA Tg (205°C vs 180°C), a 25°C higher Td (385°C vs 360°C), and halogen-free compliance. I-Speed is not halogen-free. For programs where those three attributes matter, IS580G is the direct upgrade path from I-Speed.
The comparison with FR408HR shows a different tradeoff. FR408HR has a higher frequency electrical performance (Df 0.0092 vs IS580G’s 0.006 — that’s actually IS580G being better on loss), similar Tg in TMA terms, but a lower Td (360°C vs 385°C) and no halogen-free compliance. IS580G outperforms FR408HR on every axis except cost, which is the normal tradeoff when moving to a higher-performance multi-functional resin system.
IS550H, Isola’s EV/automotive power electronics specialist, carries Td 400°C but Dk 4.43 and Df 0.016 — it’s optimized for thermal management and structural reliability in high-voltage power electronics, not for signal integrity. IS580G addresses a different market entirely, where both thermal reliability and low-loss electrical performance are required simultaneously.
The comparison against TerraGreen 400GE is worth noting. 400GE is halogen-free with Dk 3.29 and Df 0.0026 — significantly lower loss than IS580G — but its Tg is 200°C (5°C below IS580G’s DMA value) and its Td is 380°C (5°C below IS580G). If the application requires the lowest possible Df in a halogen-free material, 400GE or the higher-tier 400G grades win that comparison. If the application needs the highest available Td in a halogen-free material with good (but not ultra-low) loss, IS580G is the answer.
Processing Isola IS580G: Key Fabrication Guidelines
IS580G is FR-4 process compatible and processes similarly to other high-performance Isola materials. It shares the same general fabrication approach as I-Speed and FR408HR, which means any shop running those materials will find the transition to IS580G straightforward.
The lamination cure cycle targets approximately 60 minutes at cure temperature, consistent with Isola’s other high-performance epoxy grades. Use the full lamination cycle for both subassembly and final lamination. The material’s excellent fill and flow properties — specifically engineered as part of the Z-axis CTE improvement — mean consistent resin distribution during lamination even on complex multilayer constructions with blind/buried vias.
For prepreg handling, the same discipline applies as for all Isola high-performance materials: handle with clean gloves, store in original moisture barrier packaging, use FIFO inventory management, and move to a controlled environment immediately upon receipt. If IS580G prepreg absorbs moisture, it will depress Tg and affect flow during lamination — the same failure mode as other high-Tg prepregs.
Drilling follows standard parameters for high-performance E-glass epoxy: lower chiploads and cutting speeds than commodity FR-4, undercut drill geometries, and conservative parameters on thick boards with heavy copper inner layers. For boards above 2.5 mm total thickness, peck drilling may be required.
Desmear uses standard permanganate chemistry — no plasma treatment or sodium etch is required. This keeps IS580G accessible to the broad fabricator base familiar with standard epoxy laminate processing.
For finished boards requiring long shelf life before high-temperature lead-free assembly, package in a Moisture Barrier Bag with a Humidity Indicator Card and adequate desiccant. Process within 168 hours of opening the MBB at shop floor conditions ≤30°C/60% RH.
Target Applications for Isola IS580G
The application fit for IS580G is defined by the combination of halogen-free compliance, 205°C Tg, 385°C Td, and Df 0.006 — a combination that no other single Isola material provides in this cost tier:
Automotive Electronics: Body control modules, ADAS interface boards, telematics PCBs, and infotainment system motherboards where halogen-free is increasingly specified in automotive tier-1 supplier agreements and where thermal performance above 180°C Tg is required for underhood or high-duty-cycle applications. The T300 documentation supports automotive qualification packages that include thermal reliability testing at elevated temperatures.
Networking and Communications Infrastructure: High-layer-count backplanes and line cards for campus networking, edge computing hardware, and 5G access equipment where halogen-free compliance is specified and where Df 0.006 provides meaningful signal improvement over standard FR-4 for 5–25 Gbps per lane interfaces.
Aerospace and Defense Ground Support: Ground station electronics, mission computer PCBs, and defense electronics that combine environmental compliance requirements with high reliability demands and are not in the frequency range that requires I-Tera MT40 or Tachyon 100G class loss performance.
Industrial Automation and Control: High-reliability PLCs, motor drive control boards, industrial IoT gateway hardware, and test instrumentation where halogen-free compliance supports EU RoHS/REACH market access and where operating temperatures near or above 150°C during thermal cycling require Tg headroom above 180°C.
Computing and Storage: Server motherboards, storage controller boards, and GPU auxiliary boards where halogen-free compliance is specified at the system level and the data rates don’t justify the premium of ultra-low-loss materials. For DDR5 memory bus and PCIe Gen 4 implementations at moderate trace lengths, Df 0.006 is viable and the thermal reliability margin of IS580G’s 205°C Tg supports high-density power delivery.
For fabrication services and engineering support on boards designed with ISOLA PCB materials including IS580G, partnering with a fabricator experienced in high-reliability halogen-free laminate processing ensures the material’s full thermal and electrical performance is realized in production.
Design Considerations When Specifying IS580G
Impedance calculations use Dk 3.80: The higher Dk of IS580G compared to I-Speed (Dk 3.63) means trace widths for a given impedance target will be slightly narrower. When migrating an I-Speed design to IS580G, recalculate controlled impedance traces using IS580G’s Dk value at your operating frequency. The difference is not large — approximately 2–3% change in trace width for a typical 50 Ω microstrip — but it should be accounted for at the stack-up design stage rather than discovered at impedance testing.
Z-axis CTE for via design on thick boards: IS580G’s 1.8% total Z-axis expansion (50–260°C) is competitive with other high-performance materials. For boards above 20 layers or total thickness above 3.5 mm, verify via barrel stress calculations using IS580G’s actual Z-axis CTE values (pre-Tg: 30 ppm/°C, post-Tg: 190 ppm/°C) in your via reliability model. The pre-Tg value is what governs barrel stress during normal operating temperature cycling; the post-Tg value governs during reflow.
Halogen-free declaration and documentation: IS580G is halogen-free per IEC 61249-2-21 (Cl <900 ppm, Br <900 ppm, total halogens <1,500 ppm). Request the RoHS declaration and halogen-free certificate from Isola or your distributor for each production lot when preparing environmental compliance submissions.
Spread weave glass on all constructions: All IS580G glass is spread weave in both directions, which provides fiber weave effect mitigation on differential signal pairs. For designs operating above 5 GHz where fiber weave-induced skew is a concern, IS580G’s spread weave construction provides the same skew-reduction benefit as the ultra-low-loss grades.
Useful Resources and Data Downloads
| Resource | Type | Link |
| IS580G Official Product Page | Isola product page | isola-group.com/is580g |
| IS580G Datasheet PDF | Official datasheet | isola-group.com (PDF) |
| IS580G Dk/Df Tables PDF | Frequency data | isola-group.com (Dk/Df) |
| Isola Thermal Reliability Segment | Segment overview | isola-group.com/thermal-reliability |
| FR408HR Product Page | Comparison material | isola-group.com/fr408hr |
| I-Speed Product Page | Comparison material | isola-group.com/i-speed |
| IS550H Product Page | High-thermal EV/power | isola-group.com/is550h |
| TerraGreen 400GE Product Page | Halogen-free lower loss | isola-group.com/terragreen-400ge |
| IsoDesign Impedance Calculator | Online design tool | isola-group.com/design-tools |
| IPC-4101/140 Specification | IPC Standard | ipc.org |
| UL Product iQ (File E41625) | UL Certification DB | iq.ul.com |
Frequently Asked Questions About Isola IS580G
1. What is the glass transition temperature of IS580G, and why does the datasheet show different Tg values?
IS580G has a DMA Tg of 205°C and a TMA Tg of 190°C. These are two different measurement methods that measure related but not identical properties of the cured resin. DMA (Dynamic Mechanical Analysis) measures the viscoelastic transition of the resin and typically yields the highest Tg value. TMA (Thermomechanical Analysis) measures dimensional change and produces a lower value that is more representative of how the material behaves during thermal expansion modeling. Isola’s headline Tg of 205°C uses the DMA value, which is the appropriate number for material classification and comparison purposes. For Z-axis CTE and via reliability modeling, the TMA Tg of 190°C is the relevant input.
2. How does IS580G’s Df of 0.006 compare to standard FR-4 and other high-speed materials?
Standard FR-4 materials like Isola 370HR carry Df around 0.018–0.021 at 10 GHz. IS580G at Df 0.006 represents roughly a 70% reduction in loss tangent — approximately the same electrical performance tier as Isola I-Speed. This makes IS580G appropriate for designs running at 5–25 Gbps per lane where the loss improvement over FR-4 is needed but the cost and supply chain of ultra-low-loss materials (I-Tera MT40 at Df 0.0031, Tachyon 100G at Df 0.0021) is not justified. If your channel loss analysis shows Df 0.006 closes the link budget at your data rate and trace lengths, IS580G is the right specification to bring halogen-free compliance and high thermal reliability without paying for electrical performance you won’t use.
3. What makes IS580G’s Td of 385°C significant compared to competing materials?
Td 385°C is the highest decomposition temperature in Isola’s halogen-free high-reliability material segment, and higher than the Td of FR408HR (360°C) and I-Speed (360°C). Decomposition temperature governs the material’s behavior in worst-case thermal stress scenarios — the temperature at which the resin matrix begins irreversible chemical breakdown. A higher Td provides more margin against delamination during aggressive reflow conditions, extended soak times, and thermal qualification testing. For automotive and industrial programs requiring T300 documentation (time-to-delamination at 300°C), IS580G’s high Td directly enables passing T300 qualification with margin. The combination of high Td and >25% Z-axis CTE improvement together define IS580G’s position as a high-reliability halogen-free material, not just a halogen-free version of a standard mid-grade epoxy.
4. Is IS580G suitable for HDI and sequential lamination designs?
Yes. IS580G is explicitly rated as HDI technology compatible and supports multiple lamination cycles. The material’s excellent fill and flow properties — part of the resin system engineering that also delivers the Z-axis CTE improvement — support the void-free prepreg performance that HDI sequential lamination requires. The spread weave glass in all IS580G constructions also benefits HDI designs where fiber weave effect would otherwise affect impedance on fine-line signal layers. For programs requiring HDI with blind/buried vias, fine-line imaging, and halogen-free compliance, IS580G addresses all three requirements within a single material system.
5. What halogen-free standards does IS580G comply with, and how do I obtain compliance documentation?
IS580G is halogen-free per IEC 61249-2-21, which limits chlorine to <900 ppm, bromine to <900 ppm, and total halogens (Cl + Br) to <1,500 ppm by weight. It is also RoHS compliant per EU Directive 2011/65/EU and its 2015/863/EU amendment. Compliance documentation including Material Safety Data Sheets, Certificates of Conformance, RoHS declarations, and halogen-free declarations is available from Isola or through authorized distributors. Always request lot-specific documentation when submitting environmental compliance packages for EU market entry or automotive OEM material approval processes.
The Engineering Case for Isola IS580G
Isola IS580G earns its specification in the specific intersection where four requirements converge simultaneously: halogen-free environmental compliance, Tg well above 200°C, the highest Td in its class at 385°C, and a Df of 0.006 that represents a meaningful improvement over standard FR-4 without the cost of premium low-loss grades.
The material was released in late 2023, which means it’s still building its field qualification history. But its specifications are transparent, its IPC-4101/140 and UL E41625 certifications are in place, and it fills a gap in the Isola portfolio that previously required either compromising on thermal performance (using TerraGreen 400GE at Tg 200°C) or compromising on environmental compliance (using I-Speed or FR408HR).
For programs where those four constraints are all real — automotive infotainment, 5G access hardware, industrial control equipment targeting EU markets, high-reliability defense ground electronics — IS580G is the material to evaluate seriously.
For fabrication support and sourcing across the full range of Isola PCB materials including IS580G, visit RayPCB’s ISOLA PCB resource page.
