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Primary keyword: Isola TerraGreen 400G2 | ~2,800 words

When Isola Group unveiled the TerraGreen 400G family at DesignCon 2023, the headline claim was straightforward: halogen-free laminates that could beat the loss performance of Tachyon® 100G — the material that had been the reference point for high-speed PCB design for years — at 28 GHz. Isola TerraGreen 400G2 is the premium grade in that family and delivers the lowest Df in the trio: 0.0015 at 5, 10, and 20 GHz. For a material that also hits the halogen-free bar and processes on standard FR-4 equipment, that’s a number worth paying attention to.

This article gives PCB engineers and materials engineers the full picture — electrical properties, construction details, processing parameters, how 400G2 stacks up against its siblings and competitors, and the application scenarios where it belongs.

What Is Isola TerraGreen 400G2?

TerraGreen® 400G2 is Isola’s halogen-free material solution for next-generation 5G infrastructure, data center systems, high-end computing, wired and wireless communications, and AI applications. The material combines three specific technology choices that work together to achieve its signal performance: a novel halogen-free resin system, ultra-smooth HVLP3 (VLP1) copper foil with surface roughness ≤1.1 µm Rz JIS, and 2nd-generation ultra-low Dk glass fabric (referred to as L2 glass). Each of those three elements reduces a different loss mechanism, and you need all three firing together to hit Df 0.0015 in production.

TerraGreen® 400G2 laminate materials are Isola’s most advanced ultra-high speed, halogen-free, ultra-low loss design solution. The IPC classification is IPC-4101/134, and it carries UL File Number E41625 with full RoHS compliance.

Why the “400G2” Name Matters

The “400G” naming convention across this product family references 400 Gigabit Ethernet — the data rate generation these materials are designed to support. The “2” suffix in 400G2 designates the use of the second-generation ultra-low Dk glass, which is what separates 400G2 from the standard 400G grade. The 400GE variant uses conventional e-glass and RTF3 copper to anchor the lowest-cost position in the family. The naming makes the performance hierarchy explicit before you even open a datasheet.

Isola TerraGreen 400G2 Electrical Properties

This is the section most engineers come to first, and for good reason. Signal performance at high data rates is ultimately determined by the Dk/Df pair of the dielectric, the surface roughness of the copper foil, and the consistency of both across frequency and temperature.

Dk and Df Across Frequency

The lowest-loss material of the halogen-free trio, TerraGreen® 400G2, features typical Dk of 3.1 at 5, 10, and 20 GHz with typical Df of 0.0015 at the same three evaluation frequencies.

The flatness of those numbers across frequency is as important as the absolute value. A material whose Dk shifts significantly between 5 GHz and 20 GHz creates dispersion — phase velocity changes with frequency, pulse edges degrade, and timing margins erode. The stable Dk profile of 400G2 across that range is a meaningful design advantage for wideband channels.

The three new TerraGreen circuit materials deliver outstanding stability with temperature and frequency, maintaining constant permittivity (Dk) and loss tangent (Df) at temperatures from -55 to +125°C. For outdoor 5G base station hardware and server infrastructure that sees wide ambient swings, that thermal stability directly translates to consistent channel performance across the operating range.

Key Electrical and Thermal Properties at a Glance

Property	Typical Value	Notes
Dielectric Constant (Dk) @ 5 GHz	3.10	IPC-TM-650 / VNA extraction
Dielectric Constant (Dk) @ 10 GHz	3.10	Spread weave glass
Dielectric Constant (Dk) @ 20 GHz	3.10	Stable with frequency
Dissipation Factor (Df) @ 5 GHz	0.0015	Lowest in TerraGreen 400G family
Dissipation Factor (Df) @ 10 GHz	0.0015
Dissipation Factor (Df) @ 20 GHz	0.0015
Glass Transition Temperature (Tg)	200°C	TMA/DSC
Decomposition Temperature (Td)	380°C	TGA, 5% weight loss
IPC Specification	IPC-4101/134
UL Flammability	V-0	UL 94
UL File Number	E41625

Why Df 0.0015 Is a Significant Number

To put it in context: standard FR-4 runs Df around 0.020 at 1 GHz. Tachyon® 100G — Isola’s previously dominant high-speed digital material — runs Df around 0.0021. I-Tera® MT40, another Isola high-speed option, targets Df around 0.004. At 0.0015, TerraGreen 400G2 sits at the edge of what is achievable with glass-reinforced organic laminate technology without moving to fluoropolymer systems like PTFE. That matters enormously on long backplane traces and switch fabric channels in 400G/800G switches where channel insertion loss budgets are tight and any dielectric loss reduction directly translates to longer reach or fewer retimers.

The Three-Component Engineering: What Makes 400G2 Different

Understanding the material requires understanding the three engineering decisions that define it. This is where engineers who are comparing competing halogen-free low-loss laminates find the most useful differentiation.

The Novel Halogen-Free Resin System

Traditional low-halogen approaches to PCB laminates have historically involved tradeoffs: reactive halogen-free flame retardants can increase resin polarity, which raises Dk and Df. Isola’s approach with the TerraGreen 400G family was to engineer a novel resin system where the halogen-free flame retardancy and the low-loss electrical performance aren’t competing design goals.

Isola Group’s Chief Sales and Marketing Officer notes: “TerraGreen® 400G2 is our most advanced High Speed Digital product. We use ultra smooth copper foil and ultra low Dk glass fabric that are combined with this novel resin system for optimal performance for the next generation of high-end network and communication systems.”

The CAF (Conductive Anodic Filament) performance of this resin system is particularly noteworthy. The TerraGreen® 400G2 resin system has proven superior CAF performance on tight pitch testing. CAF performance is enhanced by the resin system’s excellent interlaminar and bond line adhesion strength. For high-density server boards and 5G radio unit substrates where via pitch has dropped to 0.8 mm or below, CAF resistance is no longer an optional nice-to-have — it’s a reliability requirement.

HVLP3 (VLP1) Ultra-Smooth Copper Foil

The copper foil type is HVLP3 (VLP1) with surface roughness ≤1.1 micron Rz JIS. At high frequencies, conductor loss from the skin effect becomes significant, and rougher copper surfaces increase effective trace resistance because the current path must follow the surface topology. HVLP3 at ≤1.1 µm Rz JIS is in the upper tier of commercially available smooth copper profiles — comparable with what other premium low-loss laminate systems specify.

The practical implication: you don’t get the full benefit of a Df 0.0015 dielectric if you pair it with standard VLP (≈2 µm) or LP copper (≈5 µm) foil. 400G2 is specified with HVLP3 from the outset precisely because the total channel loss budget includes both dielectric and conductor contributions, and matching the foil grade to the dielectric grade is the only way to realize the full electrical performance in a finished board.

2nd Generation Ultra-Low Dk Glass (L2 Glass)

The glass reinforcement in a laminate contributes directly to the effective Dk of the composite material and to fiber weave effect — the localized Dk variation that causes skew between differential pairs routed at different angles relative to the weave axis. TerraGreen® 400G2 uses 2nd generation Ultra Low Dk glass, and all TerraGreen 400G2 glass is spread weave in both directions. Spread weave glass reduces fiber weave effect by mechanically distributing the warp and fill fibers more evenly, reducing the Dk variation that differential pairs encounter depending on their routing angle. For 28 Gbaud NRZ and 56 Gbaud PAM4 channels, fiber weave effect is a real SI budget item that spread weave glass directly addresses.

The L2 glass availability is noted as a constraint on the datasheet — this is second-generation ultra-low Dk glass that is not as broadly available in the supply chain as standard e-glass or even first-generation low-Dk glass. Designers specifying 400G2 should confirm glass fabric availability with their fabricator and Isola distributor as part of the design-for-manufacturing review.

Full Specifications: Product Availability and Construction

Laminate Thickness and Copper Weight Options

Standard laminate offering: 2 to 10 mil (0.05 to 0.25 mm). Copper weight: ½, 1 and 2 oz (18, 35 and 70 µm) available. Thinner copper foil is also available.

Parameter	Standard Offering	Notes
Laminate thickness	2 to 10 mil (0.05–0.25 mm)	Thicker up to 18 mil available on some versions
Copper foil type	HVLP3 (VLP1)	≤1.1 µm Rz JIS surface roughness
Copper weight	½ oz, 1 oz, 2 oz (18, 35, 70 µm)	Thinner foil available
Prepreg	Available	Tooling of prepreg panels
Glass fabric	2nd gen Ultra Low Dk (L2) glass	Spread weave in both directions
IPC classification	IPC-4101/134

Reliability and Processing Attributes

TerraGreen 400G2 is CAF resistant, has low moisture absorption, is halogen free, is 6x 260°C reflow capable, and 6x 288°C solder float capable. Processing advantages include FR-4 process compatibility, excellent fill and flow, support for multiple lamination cycles, and HDI technology compatibility.

The “6x 288°C solder float” specification is worth noting explicitly. Lead-free assembly reflow temperatures routinely push 250–260°C peak, and solder float testing at 288°C is a proxy for the most aggressive assembly conditions. Six passes at that temperature gives PCB assemblers meaningful margin for rework and multiple assembly cycles — relevant on expensive backplane and line card PCBs where a single board revision can involve multiple assembly passes.

Isola TerraGreen 400G2 Processing Guidelines

Processing a Df 0.0015 material correctly requires respecting a few specific process differences from standard FR-4 handling. The fundamentals of the fabrication process are compatible with standard equipment, but the parameters need attention.

Lamination

TerraGreen 400G2 has been specifically designed for extremely low loss applications where the best possible electrical performance is required. In order to achieve optimal thermal and electrical performance, an ultra-low loss bond treatment and use of one of the recommended press cycles is necessary.

The lamination press cycle recommendation for dual-stage pressing calls for 100 PSI (7.0 kg/cm²) after vacuum dwell time, switching to high pressure at ≤90°C product temperature. After 30 minutes at cure temperature, pressure can be reduced to 50 PSI in a hot press. Cooling to 135–140°C at 2.8°C/min with 50 PSI pressure maintained before opening the press. The controlled cool-down rate matters for dimensional stability of the finished panel.

Imaging and Etching

TerraGreen 400G2 laminates are imaged using standard aqueous dry films and are compatible with both cupric chloride and ammoniacal etchants. No special resist chemistry is required. Routing is preferred over shearing for flash removal after lamination to minimize crazing along panel edges.

Desmear

Trials show that TerraGreen 400G2 shows good response to chemical desmear. Processing parameters used for 170°C Tg FR-4 should be used; excessive dwell time will cause etchback. Two passes of chemical desmear is recommended for high-reliability or thicker designs (>2.5 mm). A short plasma etch desmear can be used as an alternative to or in combination with permanganate, comparable to standard FR-4.

Board Storage and Packaging

TerraGreen 400G2 finished boards have low moisture sensitivity and good shelf life. Printed boards that will use high-temperature assembly and which require a long shelf life should be packaged using a Moisture Barrier Bag with a Humidity Indicator Card and adequate drying desiccant inside to prevent moisture absorption during shipment and long-term storage.

TerraGreen 400G Family Comparison: 400G2 vs 400G vs 400GE

All three grades share the same halogen-free resin system and UL V-0 rating. The differentiation comes from the glass fabric and copper foil choices, which define the loss performance and price position.

Parameter	TerraGreen 400G2	TerraGreen 400G	TerraGreen 400GE
Dk @ 10/20 GHz	3.10	3.15	3.29
Df @ 10/20 GHz	0.0015	0.0017–0.0018	0.0026
Glass Type	2nd gen Ultra Low Dk (L2)	Low Dk glass	E-glass
Copper Foil	HVLP3 (VLP1) ≤1.1 µm	HVLP3 (VLP1) ≤1.1 µm	RTF3 (<2.5 µm Rz JIS)
Tg / Td	200°C / 380°C	200°C / 380°C	200°C / 380°C
UL Rating	V-0 (E41625)	V-0	V-0
Target Use	Highest perf. HSD / RF	High-performance HSD	Cost-optimized HSD
Relative Cost	Highest	Mid	Lowest

The 400G2’s Df advantage over 400G (0.0015 vs 0.0017–0.0018) comes from the L2 glass, which has lower intrinsic loss than first-generation low-Dk glass. Whether that delta justifies the material premium depends on your channel loss budget. At >400 Gb/s SerDes data rates with long trace runs, it often does. For shorter channels or less frequency-critical designs, 400G at lower cost may be sufficient.

How Isola TerraGreen 400G2 Compares to Other Premium Low-Loss Laminates

Material	Manufacturer	Dk (typ)	Df (typ)	Halogen-Free	Tg
TerraGreen 400G2	Isola	3.10	0.0015	Yes	200°C
TerraGreen 400G	Isola	3.15	0.0017	Yes	200°C
Tachyon® 100G	Isola	3.02	0.0021	No	215°C
I-Tera® MT40	Isola	3.45	0.0040	No	200°C
Astra® MT77	Isola	3.00	0.0017	No	200°C
Megtron 7	Panasonic	3.37	0.0020	No	185°C
Rogers RO4350B	Rogers	3.48	0.0037	No	>280°C

The comparison with Tachyon 100G is instructive. Tachyon 100G delivers a slightly lower Dk (3.02 vs 3.10) but a higher Df (0.0021 vs 0.0015). The three new TerraGreen circuit materials are capable of even less loss than Tachyon 100G at 28 GHz. For engineers who already have experience with Tachyon 100G and are being asked to meet halogen-free requirements from their OEM customers, 400G2 offers a path that improves Df while satisfying the environmental requirement — without requiring process requalification of the fabrication line.

Astra® MT77 at Dk 3.00 and Df 0.0017 sits close to 400G2 on Df but is not halogen-free. For designs where halogen-free is a hard requirement from the customer specification or regional regulation, 400G2 is effectively the only Isola option in that Df range.

Target Applications for Isola TerraGreen 400G2

The application fit for this material is specific and driven directly by the combination of ultra-low Df and halogen-free qualification:

5G Infrastructure: mmWave base station radio units, Massive MIMO antenna array feed networks, fronthaul/midhaul transport equipment, and 5G small cell radios where both RF signal integrity and environmental compliance are requirements. The stable Dk from -55 to +125°C directly supports outdoor base station operating ranges.

AI Accelerator and HPC Switch Fabric: 400G and 800G switch ASICs, AI training server backplanes, and high-bandwidth memory (HBM) interconnect boards where SerDes channel loss budgets demand ultra-low loss materials across long backplane traces. The >100 Gb/s data rate target is directly aligned with current and next-generation PCIe 6.0 and Ethernet 800GbE channel requirements.

Data Center Networking: Top-of-rack and spine switches running 100G/400G optical transceiver plug interfaces, where signal integrity on the copper reach from ASIC to pluggable optical module is the design constraint.

Wired Telecom: Core router line cards, DWDM transport equipment, and access aggregation platforms where halogen-free materials are increasingly specified alongside low-loss performance requirements.

High-End Computing: Servers using high-speed DDR5 or HBM memory, multi-socket compute platforms, and any system where memory bus operating frequency has exceeded what FR-4 or I-Speed can reliably support.

For design support and fabrication using ISOLA PCB materials including the TerraGreen 400G2, working with a fabricator experienced with ultra-low-loss laminate processing is the most reliable path to achieving the material’s full electrical performance in production.

Useful Resources and Data Downloads

Resource	Type	Link
TerraGreen 400G2 Official Product Page	Isola product page	isola-group.com/terragreen-400g2
TerraGreen 400G2 Datasheet PDF	Official datasheet	isola-group.com (PDF)
TerraGreen 400G2 Processing Guide	Fabrication guide PDF	isola-group.com (Processing PDF)
TerraGreen 400G Product Page	Related product	isola-group.com/terragreen-400g
TerraGreen 400GE Product Page	Related product	isola-group.com/terragreen-400ge
Isola Tachyon 100G Product Page	Comparison material	isola-group.com/tachyon-100g
IPC-4101/134 Specification	IPC Standard	ipc.org
UL Product iQ (E41625 lookup)	UL Certification DB	iq.ul.com
PCB Directory — TerraGreen 400G2	Distributor listings	pcbdirectory.com
Signal Integrity Journal — Isola DesignCon 2023	Technical article	signalintegrityjournal.com

Frequently Asked Questions About Isola TerraGreen 400G2

1. What is the key difference between TerraGreen 400G2 and TerraGreen 400G?

Both grades share the same halogen-free resin system, HVLP3 copper foil, Tg of 200°C, and Td of 380°C. The differentiating factor is the glass fabric: 400G uses first-generation low-Dk glass, while 400G2 uses the 2nd-generation Ultra Low Dk (L2) glass. The L2 glass delivers a lower composite Dk and a lower Df — 0.0015 vs 0.0017–0.0018 at 10 GHz. If your channel loss budget requires every tenth of a millimeter of Df reduction, 400G2 is the correct choice. If first-generation Low Dk glass is sufficient and cost is a factor, 400G delivers most of the performance at a more accessible price point. Note that L2 glass availability is a supply chain consideration — verify with your fabricator before committing to 400G2 in production.

2. Is Isola TerraGreen 400G2 compatible with standard FR-4 PCB fabrication processes?

Yes, with some process parameter attention. 400G2 is FR-4 process compatible — it images with standard aqueous dry film photoresists, etches in both cupric chloride and ammoniacal etchants, and desmears with standard permanganate chemistry at 170°C Tg FR-4 dwell times. The main process differences from commodity FR-4 are: the lamination press cycle requires an ultra-low loss bond treatment and specific temperature/pressure profiles; flash removal after lamination should be done by routing rather than shearing; and two-pass desmear is recommended for boards thicker than 2.5 mm. Any fabricator experienced with high-performance laminates such as Tachyon 100G or I-Tera MT40 will have no difficulty qualifying a 400G2 process.

3. Why does TerraGreen 400G2 use HVLP3 copper foil instead of standard VLP copper?

Conductor loss from surface roughness becomes a dominant loss mechanism above 10 GHz. The skin depth at 28 GHz in copper is approximately 0.4 µm — meaning current flows almost entirely within the first micron of the copper surface at those frequencies. Standard VLP copper runs surface roughness around 2 µm Rz, and LP copper typically exceeds 5 µm Rz. Routing current through those rough surfaces increases the effective electrical path length, raising insertion loss well above what the flat-surface conductor resistance calculation would predict. HVLP3 at ≤1.1 µm Rz substantially reduces that roughness-driven insertion loss penalty. Specifying a Df 0.0015 dielectric and pairing it with standard roughness copper would leave a significant fraction of the material’s electrical potential unrealized in the finished board.

4. What are the CAF performance characteristics of TerraGreen 400G2, and why does it matter for HDI designs?

Conductive Anodic Filament (CAF) formation is an electrochemical degradation mechanism where metallic filaments grow along glass-resin interfaces under DC bias and humidity, creating leakage paths and eventual shorts between vias. In HDI boards with 0.8 mm or tighter via pitch, the probability of CAF-related failure at a given voltage bias increases as via spacing decreases. TerraGreen 400G2 has demonstrated superior CAF performance on tight pitch testing, which Isola attributes to the excellent interlaminar and bond line adhesion strength of the novel resin system. For switch fabric backplanes and AI server boards where via density is extremely high and operating voltages can be several volts across tightly spaced via fields, that CAF performance is a meaningful reliability differentiator compared to low-adhesion resin systems.

5. Is TerraGreen 400G2 suitable for RF and microwave applications, or is it purely a high-speed digital material?

400G2 is optimized for the high-speed digital (HSD) application space, and it performs well in the sub-30 GHz frequency range typical of current 5G NR FR2 (mmWave) sub-systems and high-speed SerDes channels. Isola also offers a TerraGreen 400G (RF/MW) variant specifically characterized for RF and microwave applications. For pure RF/microwave designs at frequencies above 30 GHz — phased array antenna elements, waveguide transitions, radar front ends — materials like PTFE-based laminates (Rogers RT/duroid, Taconic) or Isola’s Astra MT77 are typically more appropriate due to their lower and flatter Dk across very wide frequency ranges and lower CTE. However, for mixed-signal boards combining high-speed digital interfaces with sub-30 GHz RF functions, 400G2 is a reasonable single-material solution that avoids the cost and processing complexity of hybrid material stack-ups.

Engineering Assessment: When to Specify Isola TerraGreen 400G2

Isola TerraGreen 400G2 earns serious consideration in three specific design scenarios. First, when the OEM customer specification explicitly requires halogen-free materials and the channel data rate requires Df in the 0.0015 range — there is no other laminate in the Isola portfolio that satisfies both requirements simultaneously. Second, when an existing Tachyon 100G design is being converted to halogen-free compliance: 400G2 delivers lower Df than Tachyon 100G while satisfying the environmental requirement, making it a genuine upgrade path rather than a compromise. Third, when channel loss models for a new 400G+ switch or AI interconnect design show that Df 0.002 materials leave insufficient noise margin and the design team is not prepared to add active retimers to address the deficit.

The constraints to weigh against those scenarios: L2 glass availability is not as broad as standard glass supply chains, so qualification and production scheduling require fabricator confirmation. The material is positioned as a premium product, and the cost per panel will be materially higher than 400G or 400GE. And ultra-low-loss materials in general demand more process discipline from the fabrication shop — the board you buy is only as good as the bond treatment, press cycle, and desmear process that went into building it.

When those constraints are manageable and the application genuinely needs both halogen-free compliance and leading-edge low-loss performance, 400G2 is the material to specify.

For sourcing, fabrication support, and stack-up design assistance with Isola PCB materials including TerraGreen 400G2, visit the ISOLA PCB resource page at RayPCB.