Isola PCB Material Selection Guide: Types, Properties & Best Uses

A practical engineer’s guide to selecting the right Isola laminate for your PCB design. Covers 370HR, FR408HR, Tachyon 100G, Astra MT77, and more—with real-world application insights and comparison tables.

Why Isola Material Selection Matters

I’ve been working with PCB laminates for over a decade, and if there’s one lesson that keeps coming back, it’s this: material selection can make or break a project. You can nail the layout, perfect the impedance calculations, and still end up with a board that fails in the field—all because the laminate wasn’t right for the application.

Isola Group has been in the laminate business since 1912, and their portfolio has grown to address virtually every corner of the electronics market. From standard FR-4 replacements to ultra-low-loss materials for 5G and automotive radar, they’ve got options. The challenge? Knowing which one to pick.

This guide cuts through the datasheet jargon and gives you practical guidance on selecting Isola materials. We’ll cover the key properties you need to understand, walk through the most commonly used products, and help you match materials to applications. Whether you’re designing a consumer IoT device or a mission-critical aerospace system, you’ll find actionable information here.

Over the years, I’ve learned that material selection isn’t just an engineering decision—it’s a business decision. Choosing a premium material when standard FR-4 would suffice wastes money. But specifying a cheap laminate for a high-reliability application can cost you far more in field failures, warranty returns, and reputation damage. The goal is finding the right balance for your specific situation.

Isola PCB Design Calculator

PCBSync Engineering Tools

Select Isola Material

Dielectric Constant (Dk)

3.70

Loss Tangent (Df)

0.0120

Glass Transition (Tg)

180°C

Decomposition (Td)

340°C

CTE Z-axis

3.0%

T260/T288

>60/>30 min

FR408 is Isola's high-performance FR-4 material designed for multilayer PWB applications. It offers excellent thermal reliability, low CTE, and is ideal for high layer count designs requiring lead-free assembly compatibility.

Material Comparison Chart

Material	Dk	Df	Tg (°C)	Application
FR408	3.70	0.0120	180	High Reliability
IS410	4.00	0.0180	170	Multilayer
Astra MT77	3.00	0.0017	200	RF/Microwave
I-Tera MT40	3.45	0.0031	200	High Speed
I-Speed	3.63	0.0085	185	Low Loss

Understanding Key PCB Material Properties

Before diving into specific Isola products, let’s establish a common vocabulary. These properties appear on every laminate datasheet, and understanding them is essential for making informed decisions.

Dielectric Constant (Dk) and Dissipation Factor (Df)

The dielectric constant (Dk), also called relative permittivity, measures how much the material slows down electrical signals compared to air. A higher Dk means slower signal propagation and narrower traces for a given impedance. For most high-speed designs, you want a lower and stable Dk across your operating frequency range.

The dissipation factor (Df), or loss tangent, tells you how much signal energy gets converted to heat as it travels through the dielectric. Lower Df means less insertion loss—critical for long traces, high-frequency signals, and anything where signal integrity matters. At 10+ GHz, this becomes a dominant factor in your link budget.

Here’s what trips up many engineers: Dk and Df values on datasheets are measured at specific frequencies and conditions. A material showing Dk of 3.5 at 1 GHz might behave quite differently at 10 GHz. Always check the frequency-dependent curves when designing high-speed systems.

Another factor worth understanding: the glass weave pattern affects Dk consistency across the board. Woven glass creates periodic variations in the resin-to-glass ratio, which means Dk isn’t perfectly uniform. This becomes particularly important for differential pairs where skew can degrade signal quality. Isola addresses this with spread glass weaves in their high-performance materials—something to look for in the datasheets.

Glass Transition Temperature (Tg) and Decomposition Temperature (Td)

Tg is the temperature where the resin transitions from a rigid state to a more flexible, rubbery state. Above Tg, the material’s CTE (coefficient of thermal expansion) increases dramatically, which can stress vias and copper-to-laminate bonds. For lead-free assembly, you need a Tg of at least 170°C—and ideally higher for multiple reflow cycles.

Td (decomposition temperature) indicates when the material starts chemically breaking down. This is measured as the temperature at 5% weight loss. A higher Td provides more margin for assembly processes and gives you confidence the material won’t degrade during soldering.

Coefficient of Thermal Expansion (CTE)

CTE measures how much the material expands when heated. The Z-axis CTE is particularly important for multilayer boards because it affects via reliability. Copper has a CTE around 17 ppm/°C, while standard FR-4 can exceed 50 ppm/°C in the Z-axis above Tg. This mismatch creates stress that can crack barrel walls and lift pads over thermal cycles.

What matters most is the total Z-axis expansion through the assembly temperature range, typically expressed as a percentage from 50°C to 260°C. Materials with lower total expansion put less stress on plated through-holes and vias. For high-layer-count boards with small via diameters, this becomes a critical reliability factor. I’ve seen boards fail interconnect stress testing specifically because of poor CTE management.

Isola’s high-reliability materials like 370HR and FR408HR specifically address this with lower Z-axis CTE values, improving via reliability in demanding applications.

CAF Resistance

Conductive Anodic Filament (CAF) formation is a failure mechanism where conductive copper filaments grow along glass fiber interfaces under voltage bias and humidity. As designs get denser with tighter spacing, CAF becomes a real threat to long-term reliability. Isola has invested heavily in resin systems and glass treatments that resist CAF formation—materials like 370HR and IS550H lead the industry in CAF performance.

Material Property Classifications

Property	Standard FR-4	Mid-Tier	High-Performance
Dk (10 GHz)	4.2 – 4.5	3.5 – 4.0	3.0 – 3.5
Df (10 GHz)	> 0.020	0.008 – 0.015	< 0.005
Tg	130-150°C	170-190°C	200-260°C
Application	Consumer, < 1 GHz	1-10 GHz digital	RF/MW, >10 Gbps

Isola Product Portfolio: Material Categories

Isola organizes their products into several categories based on performance characteristics. Understanding this structure helps you narrow down options quickly.

Thermally Reliable Materials

These materials prioritize thermal performance and reliability for lead-free assembly and demanding operating environments.

370HR – Industry Standard for High Reliability

If I had to pick one Isola material that’s proven itself in the field more than any other, it’s 370HR. With a Tg of 180°C, Td of 340°C, and exceptional CAF resistance, it’s become the default choice for applications requiring high thermal reliability without exotic pricing.

Key specifications:

Tg: 180°C | Td: 340°C
Dk: 4.04 @ 2 GHz | Df: 0.021 @ 2 GHz
Z-axis CTE: 2.8% (50-260°C)
Best for: Automotive, aerospace, medical, industrial—anywhere reliability matters

The 370HR system uses high-quality E-glass fabric specifically selected for CAF resistance. It processes like standard FR-4 but delivers significantly better thermal cycling performance. I’ve used it on sequential lamination designs with excellent results.

One thing I particularly appreciate about 370HR is its availability. Unlike some specialty materials that require long lead times, 370HR is widely stocked at fabricators globally. This makes it practical for both prototype and production volumes. The consistent global supply also means you can qualify a design at one fab and transfer to another without material availability concerns.

FR408HR – Bridging Thermal and Electrical Performance

FR408HR takes the thermal reliability of 370HR and adds improved electrical performance. With a Tg of 190°C and 30% lower Df than standard high-Tg materials, it’s positioned for designs that need both thermal robustness and decent high-speed capability.

Key specifications:

Tg: 190°C | Td: 360°C
Dk: 3.68 @ 2 GHz | Df: 0.0092 @ 2 GHz
30% better Z-axis expansion than competitive products
Best for: Networking equipment, servers, telecom infrastructure

High-Speed Digital Materials

When data rates climb above 10 Gbps, insertion loss becomes a critical design constraint. These materials are engineered for low loss while maintaining processability.

I-Speed – Low Loss with FR-4 Processing

I-Speed represents an excellent balance point: significantly lower loss than standard FR-4 (Df of 0.0060 at 2 GHz) while maintaining familiar processing characteristics. It’s compatible with standard FR-4 fab processes, which keeps manufacturing costs reasonable.

Key specifications:

Tg: 180°C | Td: 360°C
Dk: 3.63 @ 2 GHz | Df: 0.0060 @ 2 GHz
Best for: 10-25 Gbps digital, high-speed backplanes, HDI designs

Tachyon 100G – Ultra-Low Loss for 100+ Gbps

When you’re designing for 100 Gbps Ethernet or next-generation data center switches, Tachyon 100G delivers the performance you need. With Dk of 3.02 and Df of 0.0021, it enables longer channel reaches and cleaner eye diagrams.

Key specifications:

Tg: 215°C | Td: 360°C
Dk: 3.02 @ 10 GHz | Df: 0.0021 @ 10 GHz
30% improvement in Z-axis CTE vs. competitive products
Best for: High-layer count backplanes, 100G+ line cards, data center equipment

I-Tera MT40 – Flexible Dk Options

I-Tera MT40 offers something unique: multiple Dk options (3.38, 3.45, 3.60, and 3.75) while maintaining consistent low-loss performance. This flexibility helps when you need to match impedances in hybrid designs or optimize trace widths for specific constraints.

Key specifications:

Tg: 215°C | Td: 360°C
Dk: 3.38-3.75 options @ 10 GHz | Df: 0.0031 @ 10 GHz
Best for: High-speed digital, RF hybrid designs, impedance-critical applications

RF/Microwave Materials

For frequencies above 10 GHz and into millimeter-wave territory, these specialized materials deliver the stability and low loss that RF designs demand.

Astra MT77 – PTFE Performance, FR-4 Processing

Astra MT77 is remarkable because it delivers electrical performance comparable to ceramic-filled PTFE materials while processing like FR-4. The ultra-low Df of 0.0017 at 10 GHz, combined with Dk stability from -40°C to +140°C through W-band frequencies, makes it ideal for automotive radar and 5G mmWave applications.

Key specifications:

Tg: 200°C | Td: 360°C
Dk: 3.00 @ 10 GHz | Df: 0.0017 @ 10 GHz
Dk stable through W-band (75-110 GHz)
Best for: 77 GHz automotive radar, 5G mmWave, satellite communications

TerraGreen & TerraGreen 400G – Halogen-Free Ultra-Low Loss

TerraGreen addresses the growing demand for environmentally compliant high-performance materials. The 400G variant is engineered for next-generation 5G infrastructure and data center applications, supporting data rates above 100 Gbps with a Df of just 0.0018 at 10 GHz.

Key specifications (TerraGreen 400G):

Tg: 200°C | Td: 380°C
Dk: 3.05 @ 10 GHz | Df: 0.0018 @ 10 GHz
Halogen-free, RoHS compliant
Best for: 5G infrastructure, AI computing, high-end servers

Specialty Materials

IS550H – Extreme Thermal Reliability for Automotive

IS550H was developed specifically for automotive electrification challenges. It handles continuous operation at 175°C and survives 2000 thermal cycles from -40°C to 175°C. The material demonstrates exceptional CAF resistance at 1500V for 1000 hours—critical for high-voltage EV applications.

Key specifications:

Continuous operating temperature: 175°C
Thermal cycling: 2000 cycles (-40°C to 175°C)
Thermal conductivity: 0.70 W/mK (enables embedded heat sinks)
Halogen-free
Best for: EV power electronics, on-board chargers, battery management systems

P95/P96 – Polyimide for Extreme Conditions

When even high-Tg epoxy isn’t enough, polyimide materials like P95 and P96 step in. With Tg of 260°C, they handle the most demanding thermal environments—think downhole drilling, engine control units, and space applications where no other material will survive.

Isola Material Comparison Table

Material	Tg (°C)	Td (°C)	Dk	Df	Category	Best Applications
370HR	180	340	4.04	0.021	Thermal	Automotive, aerospace, medical
FR408HR	190	360	3.68	0.0092	Mid-Loss	Servers, networking, telecom
I-Speed	180	360	3.63	0.0060	Low-Loss	10-25 Gbps digital, HDI
Tachyon 100G	215	360	3.02	0.0021	Ultra-Low	100G+ Ethernet, backplanes
Astra MT77	200	360	3.00	0.0017	RF/MW	77 GHz radar, 5G mmWave
TerraGreen 400G	200	380	3.05	0.0018	HF-Ultra	5G infra, AI computing
IS550H	175*	350+	~4.0	~0.015	Auto EV	EV power, BMS, chargers

*Continuous operating temp; Dk/Df values at 2 GHz unless noted

A few notes on interpreting this table: the Dk and Df values shown are typical specifications at standard test conditions. In actual designs, you’ll see variations based on resin content, glass style, and copper roughness. Always use your fabricator’s construction-specific data for impedance calculations rather than these headline numbers.

Application-Based Material Selection

Choosing the right material starts with understanding your application requirements. Here’s a practical decision framework based on common design scenarios.

Consumer Electronics & IoT

For most consumer products where cost is a significant factor and signal speeds stay under a few GHz, standard materials like IS410 or IS420 work well. These provide good thermal performance for lead-free assembly without the premium pricing of high-performance materials.

Recommended: IS410, IS420, or 370HR for higher reliability needs

Data Center & High-Speed Networking

At 25 Gbps and above, insertion loss becomes the primary constraint. For 100G Ethernet and beyond, you’re looking at Tachyon 100G or I-Tera MT40. For 10-25 Gbps applications, I-Speed or FR408HR often provide sufficient performance at lower cost.

Recommended: Tachyon 100G (100G+), I-Tera MT40 (hybrid designs), I-Speed (10-25 Gbps)

Automotive Electronics

Automotive applications span a wide range. For infotainment and body electronics, 370HR provides excellent reliability. For ADAS radar at 77 GHz, Astra MT77 is purpose-built. For EV power electronics facing extreme thermal cycling, IS550H is the go-to choice.

Recommended: 370HR (general), Astra MT77 (radar), IS550H (EV power)

Aerospace & Defense

Mission-critical applications demand proven reliability and often require extended temperature ranges. 370HR and FR408HR have extensive track records. For extreme temperatures, polyimide materials like P95/P96 may be necessary. RF systems benefit from Astra MT77’s stability through mmWave frequencies.

Recommended: 370HR (general), P95/P96 (extreme temp), Astra MT77 (RF/radar)

Medical & Industrial Equipment

Medical devices and industrial equipment typically prioritize reliability and longevity over cutting-edge performance. These products often have 10+ year service lives and must operate flawlessly in challenging environments. The key factors are consistent quality, excellent CAF resistance, and robust thermal performance for reflow and repair cycles.

Recommended: 370HR (general purpose), FR408HR (imaging equipment), IS550H (high-power industrial)

Design Tools and Resources

Isola provides several free tools that make material selection and stackup design much easier:

IsoStack Stackup Designer

The IsoStack tool (isodesign.isola-group.com/isostack) is invaluable for stackup planning. It calculates:

Layer thicknesses and dielectric constants for specific constructions
Impedance for single-ended and differential pairs
Resin content and finished thickness
Downloadable stackup visualizations for design review

Essential Datasheet Links

Always reference official datasheets for accurate specifications:

Isola Product Guide PDF: isola-group.com/wp-content/uploads/Isola_Product_Guide_Online
Individual datasheets: isola-group.com/pcb-laminates-prepreg/
Technical papers and presentations: isola-group.com/resources/
IsoDesign Studio (impedance calculator): isola-group.com/resources/design-tools/

Practical Tips for Material Selection

Work with Your Fabricator Early

Don’t finalize material selection without consulting your PCB fabricator. They know what’s in stock, what alternatives are available, and can flag potential PCB manufacturing issues. A material that looks perfect on paper might have 12-week lead times or limited prepreg thicknesses.

Consider Hybrid Constructions

You don’t always need ultra-low-loss material throughout the entire stackup. Hybrid designs using Astra MT77 for RF layers and 370HR for power/ground layers can optimize both performance and cost. Isola specifically designs materials like Tachyon 100G and Astra MT77 to be thermally compatible for hybrid builds.

Account for Manufacturing Variations

Datasheet values are typical, not guaranteed. Build margin into your design for Dk variations (±5-10% is common), thickness tolerances, and etch factors. Use the fab’s Dk/Df tables for specific constructions rather than marketing datasheet values when doing signal integrity analysis.

Don’t Over-Specify

It’s tempting to specify the best material “just to be safe,” but over-specification drives up costs without adding value. If your fastest signals are 5 Gbps, you don’t need Tachyon 100G. Match the material to the application—and document why you made that choice for future reference.

Understand the Cost Hierarchy

As a rough guide, material costs increase as you move from standard FR-4 to thermally robust materials (370HR, FR408HR), then to low-loss materials (I-Speed, I-Tera MT40), and finally to ultra-low-loss and RF materials (Tachyon 100G, Astra MT77). The premium for high-performance materials can be 3-10x standard FR-4, so make sure the application actually requires that performance level.

Plan for Second Sourcing

While this guide focuses on Isola materials, smart procurement planning includes identifying equivalent materials from other suppliers. Most Isola materials have roughly equivalent offerings from Panasonic (Megtron series), Shengyi (various), or other suppliers. Your fabricator can help identify appropriate alternatives, which provides supply chain resilience and potential cost leverage.

Frequently Asked Questions

1. What’s the difference between 370HR and FR408HR?

Both are high-reliability materials, but FR408HR offers about 30% lower dielectric loss (Df of 0.0092 vs 0.021). If your design involves signals above 3-5 GHz or you’re concerned about insertion loss, FR408HR is the better choice. For purely thermal reliability with cost sensitivity, 370HR remains the industry standard.

2. Can I mix different Isola materials in one stackup?

Yes, and Isola designs many of their products to be compatible for hybrid constructions. The key is matching CTE characteristics to avoid warpage and delamination. Materials like Tachyon 100G and Astra MT77 share similar thermal properties specifically to enable hybrid builds. Always verify compatibility with your fabricator and use IsoStack to model the stackup.

3. How do I choose between I-Speed, I-Tera MT40, and Tachyon 100G?

It comes down to data rate and loss budget. I-Speed works well up to about 25 Gbps with its Df of 0.006. I-Tera MT40 (Df of 0.0031) handles higher speeds and offers multiple Dk options for impedance flexibility. Tachyon 100G (Df of 0.0021) is optimized for 100 Gbps and beyond. Run your signal integrity simulations with actual trace lengths to determine what loss level you can tolerate.

4. Is Astra MT77 really comparable to PTFE performance?

For many applications, yes. With Dk of 3.0 and Df of 0.0017 at 10 GHz—stable through W-band—Astra MT77 rivals ceramic-filled PTFE materials. The big advantage is processability: it uses standard FR-4 fabrication methods, reducing cost and improving dimensional stability. For 77 GHz automotive radar and similar applications, it’s become the material of choice.

5. What material should I use for a design that needs to survive harsh automotive environments?

For standard automotive applications, 370HR provides excellent reliability with proven thermal cycling performance. For under-hood or EV power electronics facing extreme temperatures (up to 175°C continuous), IS550H is specifically designed for this environment with exceptional thermal cycling capability and CAF resistance at high voltage. For ADAS radar, Astra MT77 handles both the thermal requirements and 77 GHz electrical performance.

Conclusion

Selecting the right Isola material isn’t about finding the “best” laminate—it’s about matching material properties to your specific application requirements. The company’s portfolio spans everything from cost-effective general-purpose materials to ultra-low-loss options for cutting-edge 5G and automotive radar applications.

Start by understanding your key constraints: What are your operating frequencies and data rates? What thermal environment will the board face? What reliability requirements must you meet? What’s your budget? Armed with that information and the comparison tables in this guide, you can narrow down options quickly.

Remember to leverage Isola’s free tools—particularly IsoStack for stackup design—and work with your fabricator early in the design process. Material selection is ultimately a team effort, and getting it right upfront saves significant time and cost compared to discovering problems during validation or, worse, in the field.

The electronics industry keeps pushing toward higher frequencies, faster data rates, and denser designs. Isola continues to develop new materials to meet these challenges. Stay current with their latest offerings, and don’t hesitate to reach out to their technical support team for guidance on demanding applications—they’ve helped me solve more than a few tricky material selection problems over the years.

Looking Ahead: Emerging Requirements

As we move toward 800G data center switches, 6G research frequencies, and increasingly sophisticated automotive electronics, material requirements will continue to evolve. Halogen-free compliance is becoming standard rather than optional. Higher operating temperatures from dense packaging demand better thermal management. And sustainability considerations are influencing material development in ways we’re only beginning to see. Staying informed about these trends will help you make better material selection decisions today that won’t paint you into a corner tomorrow.