Compare ITEQ high-Tg FR-4 laminates — IT-158, IT-170G, IT-180A — with full specs, IPC-4101 slash sheets, and a practical selection guide for lead-free PCB designs.

Most PCB engineers have a love-hate relationship with FR-4. It’s cheap, widely available, and works fine for a huge range of applications — until it doesn’t. The moment you push into lead-free assembly, high layer counts, or tighter thermal budgets, standard FR-4 starts showing its limits. That’s where ITEQ high Tg FR-4 materials come in, and understanding the differences between ITEQ’s laminate grades is genuinely useful knowledge for anyone specifying boards today.

This guide covers ITEQ’s standard and high-Tg FR-4 laminate lineup in practical detail — what the grades are, what the specs actually mean, when to use which material, and how to specify them correctly. Written from an engineering perspective, not a marketing one.

What Makes a Laminate “High-Tg FR-4”

Before getting into ITEQ’s specific products, it’s worth being precise about what “high-Tg FR-4” actually means, because the term gets used loosely.

FR-4 is a material classification, not a single product. It defines a glass-reinforced epoxy laminate that meets UL 94 V-0 flammability requirements. The “FR” stands for flame retardant, and the “4” refers to the woven glass reinforcement. Within that classification, there’s enormous variation in resin chemistry, Tg, Td, Dk, Df, and other properties.

Tg: What It Is and Why It Matters

Tg — glass transition temperature — is the temperature at which the epoxy resin transitions from a rigid, glassy state to a softer, rubbery state. Below Tg, the material behaves predictably. Above Tg, the Z-axis CTE increases dramatically, dimensional stability degrades, and mechanical properties drop off.

For PCB reliability, Tg matters in two main scenarios:

Lead-free assembly: Peak reflow temperatures of 260°C+ put thermal stress on the laminate. While the board doesn’t stay at peak temperature long enough to reach Tg during a single reflow cycle, cumulative thermal cycling and multiple reflow passes stress materials with lower Tg more severely.

Operating temperature: Boards in industrial, automotive, or high-power applications may see sustained elevated temperatures in service. If the operating temperature approaches Tg, you’ll see accelerated degradation.

Standard vs. High-Tg: The Practical Dividing Line

Category	Tg Range	Typical Use Case
Standard FR-4	130–150°C	Consumer electronics, tin-lead assembly
Mid-Tg FR-4	150–160°C	Lead-free compatible, general commercial
High-Tg FR-4	170–180°C	Lead-free, multilayer, industrial
Very High-Tg	180°C+	High-reliability, demanding thermal environments

The industry generally considers 170°C Tg the threshold for “high-Tg” in the context of lead-free assembly. ITEQ’s lineup spans all of these categories.

ITEQ’s FR-4 Laminate Lineup: Full Overview

ITEQ PCB materials cover a wide range of performance tiers within the FR-4 family. Here’s the full picture of their standard and high-Tg offerings.

ITEQ Standard Tg Materials

IT-158: The Workhorse

IT-158 is ITEQ’s standard mid-Tg epoxy laminate — the product that competes directly with Shengyi S1141, Kingboard KB-6160, and similar mainstream FR-4 materials. It’s the default choice for cost-sensitive, general-purpose multilayer boards.

IT-158 Key Specifications:

Property	Value	Test Method
Tg (DSC)	150°C	IPC-TM-650 2.4.25
Td	310°C	IPC-TM-650 2.4.24.6
Dk @ 1 GHz	4.60	IPC-TM-650 2.5.5.5
Df @ 1 GHz	0.020	IPC-TM-650 2.5.5.5
Z-axis CTE (below Tg)	60 ppm/°C	IPC-TM-650 2.4.41
Peel strength (1 oz Cu)	≥1.05 N/mm	IPC-TM-650 2.4.8
Moisture absorption	≤0.35%	IPC-TM-650 2.6.2
Flammability	UL 94 V-0	UL 94
IPC-4101 slash sheet	/24	—

IT-158 is lead-free compatible for standard assembly processes, but for boards with high layer counts (12L+) or multiple reflow passes, the 150°C Tg starts to feel marginal. The Td of 310°C is adequate but not generous.

When to use IT-158:

4–8 layer commercial boards

Single or double reflow, standard lead-free process

Cost is a primary driver

Operating temperature below 100°C

IT-158G: Halogen-Free Version

IT-158G is the halogen-free variant of IT-158, qualified to IPC-4101 /92. Same performance tier, different resin chemistry to eliminate bromine and chlorine. Required for products targeting European markets under RoHS/WEEE or for customers with explicit halogen-free requirements.

The Tg on IT-158G is similar to IT-158, but halogen-free resins sometimes behave slightly differently in processing — particularly in terms of drill quality and lamination parameters. Confirm with your fabricator that they have experience with halogen-free materials if this is your first time specifying them.

ITEQ High-Tg FR-4 Materials

This is where ITEQ’s lineup gets more interesting from an engineering standpoint.

IT-170G: The High-Tg Standard

IT-170G is ITEQ’s primary high-Tg FR-4 material and one of their most widely used products globally. It’s the go-to choice for lead-free multilayer boards where you need reliable thermal performance without stepping up to specialty materials.

IT-170G Key Specifications:

Property	Value	Test Method
Tg (DSC)	170°C	IPC-TM-650 2.4.25
Td	335°C	IPC-TM-650 2.4.24.6
Dk @ 1 GHz	4.60	IPC-TM-650 2.5.5.5
Df @ 1 GHz	0.019	IPC-TM-650 2.5.5.5
Z-axis CTE (below Tg)	55 ppm/°C	IPC-TM-650 2.4.41
Z-axis CTE (above Tg)	240 ppm/°C	IPC-TM-650 2.4.41
Peel strength (1 oz Cu)	≥1.05 N/mm	IPC-TM-650 2.4.8
Moisture absorption	≤0.35%	IPC-TM-650 2.6.2
Flammability	UL 94 V-0	UL 94
IPC-4101 slash sheet	/26	—

The jump from IT-158 to IT-170G gives you 20°C more Tg and a meaningfully better Td (335°C vs. 310°C). That Td improvement is actually more important than the Tg bump for lead-free reliability — it gives you more margin against decomposition during peak reflow.

When to use IT-170G:

8–20+ layer multilayer boards

Lead-free assembly with multiple reflow passes

Boards with high via density where Z-axis CTE matters

Industrial or telecom applications with elevated operating temperatures

Any design where you’d previously specify “high-Tg FR-4” generically

IT-170GA: Halogen-Free High-Tg

IT-170GA is the halogen-free version of IT-170G, qualified to IPC-4101 /93. For designs that need both high-Tg performance and halogen-free compliance, this is the material. Performance is essentially equivalent to IT-170G with the resin chemistry adjusted for halogen-free compliance.

IT-180A: Very High-Tg for Demanding Applications

IT-180A steps up to 180°C Tg, targeting applications where IT-170G’s thermal margin isn’t sufficient. This includes high-layer-count backplanes, boards that see sustained elevated temperatures in service, and designs that go through more than two reflow cycles.

IT-180A Key Specifications:

Property	Value	Test Method
Tg (DSC)	180°C	IPC-TM-650 2.4.25
Td	350°C	IPC-TM-650 2.4.24.6
Dk @ 1 GHz	4.60	IPC-TM-650 2.5.5.5
Df @ 1 GHz	0.018	IPC-TM-650 2.5.5.5
Z-axis CTE (below Tg)	50 ppm/°C	IPC-TM-650 2.4.41
Moisture absorption	≤0.30%	IPC-TM-650 2.6.2
Flammability	UL 94 V-0	UL 94
IPC-4101 slash sheet	/26	—

The lower Z-axis CTE (50 ppm/°C vs. 55 ppm/°C for IT-170G) is a meaningful improvement for high-aspect-ratio vias. In a 3.2mm thick board with 0.3mm drill, the via barrel stress during thermal cycling is significantly affected by Z-axis CTE. IT-180A’s improvement here translates to better via reliability in thick, high-layer-count designs.

When to use IT-180A:

20+ layer backplanes and thick multilayer boards

High-aspect-ratio vias (aspect ratio > 10:1)

Boards with sustained operating temperatures above 100°C

Multiple reflow cycles (3+) or rework-intensive assembly processes

High-reliability applications where via barrel cracking is a known failure mode

ITEQ High-Tg FR-4 Comparison Table

Product	Tg (DSC)	Td	Dk @1GHz	Df @1GHz	Z-CTE (below Tg)	Halogen-Free	IPC-4101
IT-158	150°C	310°C	4.60	0.020	60 ppm/°C	No	/24
IT-158G	150°C	310°C	4.60	0.020	60 ppm/°C	Yes	/92
IT-170G	170°C	335°C	4.60	0.019	55 ppm/°C	No	/26
IT-170GA	170°C	335°C	4.60	0.019	55 ppm/°C	Yes	/93
IT-180A	180°C	350°C	4.60	0.018	50 ppm/°C	No	/26

Understanding Tg Measurement Methods: DSC vs. TMA

One thing that trips up engineers when comparing laminates across manufacturers is that Tg can be measured by different methods, and the results are not the same number.

The two most common methods are:

DSC (Differential Scanning Calorimetry): Measures the heat flow change as the material transitions. Generally gives a lower Tg value. This is the method specified in IPC-TM-650 2.4.25 and is the standard reference for IPC-4101 slash sheet compliance.

TMA (Thermomechanical Analysis): Measures dimensional change vs. temperature. Generally gives a higher Tg value than DSC for the same material — typically 10–15°C higher.

When ITEQ publishes Tg of 170°C for IT-170G, that’s the DSC value. If you see a competitor claiming 185°C Tg for a similar material, check whether they’re using TMA. A 170°C DSC Tg and a 185°C TMA Tg can be the same material measured differently.

Always compare Tg values using the same measurement method. For IPC-4101 compliance, DSC is the reference method.

Thermal Reliability in Lead-Free Assembly: What the Numbers Mean in Practice

The combination of Tg and Td determines how a laminate behaves through lead-free assembly. Here’s how to think about it practically.

The Lead-Free Reflow Profile

A typical lead-free reflow profile peaks at 245–260°C, with time above liquidus (TAL) of 30–60 seconds. The board doesn’t stay at peak temperature long, but the thermal shock is significant, and most products go through at least two reflow passes (top and bottom side).

Why Td Matters More Than Tg for Assembly

During reflow, the board temperature exceeds the Tg of even high-Tg materials. IT-170G has a Tg of 170°C — the board goes well above that during reflow. What prevents damage is:

The short time at peak temperature (the material doesn’t have time to fully transition)

The Td being well above the peak reflow temperature (decomposition doesn’t occur)

A material with Tg of 170°C and Td of 335°C (like IT-170G) handles lead-free reflow reliably. A material with Tg of 150°C and Td of 310°C (like IT-158) is more marginal, especially for thick boards or multiple reflow passes.

Via Reliability and Z-Axis CTE

The other thermal reliability concern is via barrel cracking during thermal cycling in service. This is driven by Z-axis CTE mismatch between the copper barrel and the laminate.

Copper has a CTE of about 17 ppm/°C. FR-4 laminates have Z-axis CTE of 50–70 ppm/°C below Tg and 200–300 ppm/°C above Tg. The mismatch puts the via barrel in tension during heating and compression during cooling. Over thousands of thermal cycles, this causes fatigue cracking.

Higher-Tg materials generally have lower Z-axis CTE below Tg, which reduces the mismatch and improves via fatigue life. IT-180A’s 50 ppm/°C Z-axis CTE vs. IT-158’s 60 ppm/°C is a 17% improvement — meaningful for high-cycle-count applications.

How to Select the Right ITEQ High-Tg FR-4 Grade

Here’s a practical decision framework for choosing between ITEQ’s FR-4 grades.

Selection Decision Tree

Step 1: Does your design require halogen-free materials?

Yes → Use IT-158G (/92), IT-170GA (/93)

No → Continue to Step 2

Step 2: What is your layer count and board thickness?

≤8 layers, ≤2.0mm → IT-158 may be sufficient

8–16 layers or 2.0–3.2mm → IT-170G is the right baseline

16+ layers or >3.2mm → Consider IT-180A

Step 3: How many reflow passes does your assembly process require?

1–2 passes, standard lead-free → IT-170G is adequate

3+ passes or rework-intensive → IT-180A provides better margin

Step 4: What is the operating temperature of the end product?

Below 85°C sustained → IT-170G is fine

85–105°C sustained → IT-170G with margin review

Above 105°C sustained → IT-180A or consider polyimide

Step 5: Are there specific reliability requirements (IPC-6012 Class 3, automotive, etc.)?

IPC-6012 Class 2 → IT-170G meets requirements

IPC-6012 Class 3 → IT-180A preferred, verify with your customer

Automotive (AEC-Q200 adjacent) → Review IT-150DA or IT-180A depending on requirements

Cost vs. Performance Tradeoff

Material	Relative Cost	Performance Tier	Best Fit
IT-158	$	Standard	Cost-driven, simple boards
IT-170G	$$	High-Tg	Most commercial multilayer
IT-180A	$$$	Very High-Tg	High-reliability, thick boards

The cost delta between IT-158 and IT-170G is typically 15–25% on the laminate itself, which translates to a smaller percentage of total board cost. For most designs, the reliability improvement of IT-170G over IT-158 is worth the modest cost increase. The jump to IT-180A is more significant in cost and is only justified when the application genuinely demands it.

Fabrication Considerations for ITEQ High-Tg FR-4

High-Tg FR-4 materials process similarly to standard FR-4, but there are a few things worth knowing.

Drilling

Higher-Tg resins are generally harder and more abrasive than standard FR-4. Drill bit wear is slightly higher, and drill parameters (feed rate, spindle speed, chip load) may need adjustment compared to standard FR-4. Most fabricators with experience in high-Tg materials have this dialed in, but it’s worth confirming if you’re working with a new shop.

Lamination

IT-170G and IT-180A require slightly higher lamination temperatures and pressures than standard FR-4 to achieve full cure. The prepreg cure cycle needs to be matched to the laminate grade. Using IT-170G prepreg with IT-158 core (or vice versa) in a hybrid stackup requires careful process validation.

Desmear and Via Processing

High-Tg resins can be more resistant to desmear chemistry, which is actually a good thing — it means cleaner via walls and better plating adhesion. But it also means that desmear process parameters need to be validated for the specific material. Plasma desmear is generally more effective than permanganate for high-Tg materials.

Storage and Handling

ITEQ prepregs should be stored at 5–22°C with relative humidity below 50%. Out-time (time at room temperature before lamination) affects resin flow and cure characteristics. Follow ITEQ’s published storage and handling guidelines — exceeding out-time limits can result in poor lamination quality.

Useful Resources for ITEQ High-Tg FR-4 Selection

ITEQ Official Resources

ITEQ Product Datasheets: iteq.com.tw/en/product.php — full specifications for all ITEQ laminates and prepregs, including Tg, Td, Dk, Df, and IPC-4101 slash sheet qualifications

ITEQ Technical Support: Available through their regional offices for stackup design assistance and material selection guidance

IPC Standards

IPC-4101D: Specification for Base Materials for Rigid and Multilayer Printed Boards — the primary standard for laminate qualification; purchase from ipc.org

IPC-TM-650: Test methods for Tg (2.4.25), Td (2.4.24.6), Dk/Df (2.5.5.5), CTE (2.4.41) — free download from IPC

IPC-6012E: Qualification and Performance Specification for Rigid Printed Boards — defines Class 2 and Class 3 requirements that drive material selection

IPC-2221B: Generic Standard on Printed Board Design — includes material selection guidance

PCB Design and Simulation Tools

Polar Instruments Si9000e: Impedance and loss simulation with laminate database — polarinstruments.com

Saturn PCB Toolkit: Free tool for impedance, via, and thermal calculations — saturnpcb.com

IPC Stackup Designer: Web-based tool for multilayer stackup planning

Industry Reference

IPC-7711/7721: Rework and repair standard — relevant for understanding how material Tg affects rework temperature limits

JEDEC JESD22-A104: Temperature cycling test standard — useful for understanding how Z-axis CTE drives via reliability requirements

FAQs: ITEQ High-Tg FR-4

Q1: Is ITEQ IT-170G a direct drop-in replacement for standard FR-4 in my existing design?

For most designs, yes. IT-170G processes on the same equipment as standard FR-4, uses the same copper foil options, and is compatible with standard lead-free assembly processes. The main thing to verify is that your fabricator has IT-170G in stock and that your stackup impedance targets don’t need adjustment — the Dk of IT-170G (4.60 @ 1 GHz) is essentially the same as standard FR-4, so impedance calculations don’t change. The upgrade is primarily in thermal reliability, not electrical performance.

Q2: My fabricator is offering “high-Tg FR-4” without specifying the brand. Should I be concerned?

It depends on your application. For general commercial boards, a generic high-Tg FR-4 meeting IPC-4101 /26 is usually fine. If you want to ensure you’re getting ITEQ material specifically — for supply chain consistency, qualification traceability, or because you’ve validated ITEQ material in your design — specify it explicitly on your fabrication drawing: “ITEQ IT-170G or equivalent per IPC-4101 /26.” This gives the fabricator flexibility while ensuring the material meets your performance baseline.

Q3: What’s the actual reliability difference between IT-170G and IT-180A for a 16-layer board?

For a 16-layer board going through standard two-pass lead-free assembly and operating below 85°C, IT-170G is typically sufficient. The improvement with IT-180A becomes meaningful when you have high-aspect-ratio vias (>10:1), more than two reflow passes, operating temperatures above 100°C, or IPC-6012 Class 3 requirements. If none of those conditions apply, IT-170G gives you good reliability at lower cost. If you’re on the fence, run the via reliability calculation using the actual Z-axis CTE values and your thermal cycling profile — the numbers will tell you whether the upgrade is justified.

Q4: Does ITEQ IT-170G meet automotive requirements?

IT-170G is not specifically qualified to automotive standards like AEC-Q200. For automotive applications, ITEQ’s IT-150DA (which has enhanced CAF resistance and is designed for automotive environments) or materials from their automotive-specific lineup are more appropriate. The key automotive laminate requirements beyond Tg include CAF resistance (critical for fine-pitch, high-voltage designs), moisture resistance, and qualification to IPC-6012 Class 3 or equivalent. Confirm specific automotive qualification requirements with ITEQ’s application engineering team.

Q5: How do I specify ITEQ IT-170G on my fabrication drawing to ensure the right material is used?

A clear fab note would read: “Base laminate: ITEQ IT-170G or approved equivalent per IPC-4101 /26. Tg minimum 170°C by DSC (IPC-TM-650 2.4.25). Td minimum 335°C (IPC-TM-650 2.4.24.6). Certificate of Conformance required with each shipment.” This covers the material identity, the performance standard it must meet, the specific thermal properties you require, and the documentation you need for traceability. If halogen-free is required, add: “Halogen-free per IEC 61249-2-21, IPC-4101 /93.”

Closing Thoughts

ITEQ’s high-Tg FR-4 lineup — IT-170G in particular — has become a reliable workhorse for commercial multilayer PCB production. It hits the right balance of thermal performance, fabrication compatibility, and cost for the majority of lead-free multilayer designs. IT-180A is there when you need more margin, and the halogen-free variants cover the regulatory requirements that come with European and consumer electronics markets.

The key takeaway for engineers: don’t default to standard FR-4 for lead-free multilayer designs just because it’s familiar. The cost delta to IT-170G is small, the reliability improvement is real, and the fabrication process is essentially identical. For most commercial multilayer boards today, IT-170G should be your baseline, not your upgrade.

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A complete engineering guide to ITEQ high-Tg FR-4 laminates — covering IT-158, IT-170G, and IT-180A specifications, IPC-4101 slash sheet qualifications, lead-free assembly reliability, and how to select the right grade for your PCB design.

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Compare ITEQ high-Tg FR-4 laminates — IT-158, IT-170G, IT-180A — with full specs, IPC-4101 slash sheets, and a practical selection guide for lead-free PCB designs.