IPC-4412: Complete Guide to Woven E-Glass Fabric for PCBs

Every PCB you’ve ever designed sits on a foundation of woven glass fabric. Whether it’s a simple two-layer board or a complex 24-layer HDI stackup, the glass reinforcement determines mechanical strength, electrical performance, and manufacturability. Yet most engineers never think about the glass fabric specification that makes it all possible.

IPC-4412 is the standard that defines woven E-glass fabrics for printed circuit boards. If you’ve ever wondered why your fabricator uses 1080 prepreg versus 2116, or what those yarn designations like “ECG 75-1/0” actually mean, this guide will give you the answers. Understanding IPC-4412 helps you make better material choices, especially when designing high-speed circuits where fiber weave effects can ruin signal integrity.

What Is IPC-4412?

IPC-4412 is officially titled “Specification for Finished Fabric Woven from ‘E’ Glass for Printed Boards.” Published by IPC (Association Connecting Electronics Industries), this standard covers the requirements for woven glass fiber fabrics used as reinforcement in PCB laminates and prepregs.

The current version is IPC-4412C, released in September 2021. This specification determines the nomenclature, definitions, general and chemical requirements for the glass, and physical requirements for finished woven glass fiber fabrics. All fabrics covered by IPC-4412 are plain weave construction.

What IPC-4412C Covers

The standard provides comprehensive tables describing each fabric style in detail, including:

• Yarn types used (warp and fill)
• Number of yarns per unit area (thread count)
• Basis weight (mass per unit area)
• Nominal thickness
• Breaking strength requirements

IPC-4412 is referenced by IPC-4101 (base materials for rigid boards) and works alongside related reinforcement standards like IPC-4411 (nonwoven para-aramid) and IPC-4130 (nonwoven E-glass mat).

Understanding E-Glass Fiber

Before diving into fabric styles, let’s clarify what E-glass actually is and why it dominates PCB reinforcement.

What Is E-Glass?

E-glass (electrical grade glass) is a borosilicate glass composition optimized for electrical insulation and mechanical strength. The “E” designation comes from its original development for electrical applications. E-glass composition typically includes:

Key E-Glass Properties

E-glass is cost-effective, readily available, and provides an excellent balance of electrical and mechanical properties for most PCB applications. For high-frequency designs requiring lower Dk, specialty glasses like NE-glass (Dk ~4.4-4.6) are available but at higher cost.

Glass Yarn Nomenclature System

One of the most confusing aspects of glass fabrics is the yarn designation system. IPC-4412 uses a standardized nomenclature that, once understood, tells you everything about the yarn construction.

Decoding Yarn Designations

A typical yarn designation like “ECG 75-1/0” breaks down as follows:

Filament Diameter Codes

The third letter indicates the individual glass filament diameter:

Understanding Yarn Weight

The number after the letters indicates yarn weight in terms of yardage. For example:

• ECG 75 = 7,500 yards per pound (finer yarn)
• ECG 150 = 15,000 yards per pound (very fine yarn)
• ECD 450 = 45,000 yards per pound (extremely fine yarn)
• ECD 900 = 90,000 yards per pound (ultra-fine yarn)

Higher numbers mean finer, lighter yarns. This directly affects the resulting fabric thickness and weight.

Common Glass Fabric Styles per IPC-4412

IPC-4412 defines numerous fabric styles, but a handful dominate PCB manufacturing. Here are the most commonly used styles:

Style 106

Style 106 is the thinnest commonly used glass fabric. Its high resin content (~70%) provides smooth surfaces ideal for fine-line imaging. Used primarily in thin cores and prepregs for HDI applications.

Style 1080

Style 1080 offers a good balance between thinness and structural integrity. Popular for multilayer boards where moderate thickness buildup is needed. Resin content typically around 60%.

Style 2116

Style 2116 is a workhorse fabric offering excellent dimensional stability with moderate thickness. Thread count is more balanced (nearly square weave), which helps reduce fiber weave effect in high-speed designs. Resin content approximately 50%.

Style 7628

Style 7628 is the heaviest common fabric. It’s the most economical choice for building thickness in rigid laminates. However, its open weave pattern creates larger resin pockets, which can cause drilling issues with small holes and increased fiber weave effect.

Glass Style Comparison Table

How Glass Style Affects Prepreg and Laminate Properties

The glass fabric style directly impacts finished prepreg and laminate characteristics. Understanding these relationships helps you make informed material selections.

Thickness and Resin Content

Lighter glass fabrics (106, 1080) have higher resin content percentages because less glass occupies the cross-section. This affects:

• Dielectric constant: Higher resin content generally means lower composite Dk
• Surface smoothness: More resin creates smoother surfaces for fine-line etching
• Drilling: Higher resin content improves small-hole drilling quality

Dimensional Stability

Heavier fabrics (2116, 7628) provide better dimensional stability because:

• More glass fiber constrains resin movement during thermal cycles
• Higher fiber content reduces CTE in X-Y plane
• Greater structural rigidity minimizes warpage

Cost Considerations

Heavier fabrics cost less per unit thickness because:

• Fewer fabric layers needed to achieve target thickness
• Faster lamination cycles (fewer plies to handle)
• Lower resin consumption per thickness unit

However, this cost advantage disappears when drilling small vias or routing fine traces, where heavier fabrics cause quality issues.

The Fiber Weave Effect and IPC-4412 Glass Styles

For high-speed digital and RF designs, the fiber weave effect (FWE) is a critical consideration directly related to glass fabric selection per IPC-4412.

What Causes Fiber Weave Effect

PCB laminates are not homogeneous materials. The woven glass fabric creates a periodic structure of:

• Glass bundles (Dk ≈ 6.0-6.6)
• Resin-filled gaps (Dk ≈ 3.0-3.5)

When a trace routes over glass-rich areas versus resin-rich areas, the signal sees different effective dielectric constants. This causes:

• Intra-pair skew: Differential pair signals arrive at different times
• Impedance variations: Local Dk changes affect characteristic impedance
• Resonances: At high frequencies, the periodic structure can create cavity resonances

Glass Style Impact on Skew

Open weave styles like 7628 create larger differential Dk regions, increasing skew potential. Tighter weaves like 106 and 1080 minimize the glass-resin Dk variation.

Mitigation Strategies

When fiber weave effect is a concern:

1. Use tighter weave styles (1080 or 2116 instead of 7628)
2. Specify spread glass fabrics when available
3. Consider NE-glass (lower Dk contrast with resin)
4. Route traces at angles to average out Dk variations
5. Request panel rotation (~10-12°) from your fabricator

Physical and Chemical Requirements in IPC-4412

IPC-4412 specifies requirements beyond just dimensions. These quality parameters ensure consistent laminate performance.

Physical Requirements

Finish Requirements

Glass fabrics require surface treatment (finish or sizing) to ensure proper resin adhesion. IPC-4412 addresses:

• Silane coupling agent compatibility
• Heat cleaning requirements
• Moisture content limits
• Finish weight specifications

Proper finish is critical—inadequate finish causes delamination, while excessive finish can interfere with resin flow during lamination.

Visual Quality Requirements

The standard defines acceptable limits for:

• Broken or missing yarns
• Contamination (foreign material)
• Weave distortions
• Splice frequency and marking

Quality Assurance per IPC-4412

IPC-4412 includes quality assurance provisions ensuring fabric consistency batch-to-batch.

Testing Requirements

Certification and Traceability

Fabric suppliers must provide:

• Certificate of conformance to IPC-4412
• Lot traceability information
• Test data for critical parameters

This traceability is essential for aerospace, military, and medical applications where material qualification is mandatory.

Read more IPC Standards:

IPC Standards Explained: A Comprehensive Guide to PCB & Electronics Assembly Standards

IPC 2615 Standard Explained: PCB Dimensioning & Tolerancing Requirements

MIL-STD-2000A: Military Soldering Standards for Electronic Assemblies

MIL-STD-1686: ESD Control Program Requirements for Military Electronics

IPC 1791 Standard: Everything You Need to Know About Trusted PCB Certification

MIL-STD-883: Complete Guide to Microelectronics Test Methods

J-STD-048 Explained: Complete Guide to Product Discontinuance Notifications

MIL-STD-750: Semiconductor Device Test Methods Explained

MIL-STD-454: General Requirements for Military Electronic Equipment

IPC 9194: Complete Guide to SPC for PCB Assembly Manufacturing

MIL-STD-202: Electronic Component Testing Methods & Procedures

IPC 4110: Complete Guide to Cellulose Paper Specs for Printed Circuit Boards

Boundary Scan Testing (JTAG) in PCB Design: A Complete DFT Guide

Axiomtek IPC-950 Review: Specs, Features & Performance [2026 Guide]

MIL-PRF-55681: Military Ceramic Chip Capacitor Specification Guide

Related IPC Standards

IPC-4412 works within a broader family of PCB material specifications:

Selecting the Right Glass Style for Your Design

Choosing appropriate glass fabric involves balancing multiple factors:

Decision Matrix

Working with Your Fabricator

When specifying materials:

1. Communicate your priorities (cost, performance, reliability)
2. Specify glass style if critical (don’t leave to fabricator default)
3. Discuss alternatives when preferred style unavailable
4. Request stackup review for high-speed designs

Useful Resources for IPC-4412

Official Documents

• IPC-4412C Standard: IPC Store
• IPC-4101 Base Materials: IPC Store
• IPC-EG-140 Glass Yarn: IPC Store

Standards Databases

• GlobalSpec/Engineering360: IPC-4412 Overview
• IHS Markit: IPC-4412 Documentation

Technical References

Glass Fabric Suppliers

Frequently Asked Questions About IPC-4412

What is the difference between IPC-4412 and IPC-4101?

IPC-4412 specifies the woven E-glass fabric used as reinforcement, while IPC-4101 specifies complete laminate and prepreg materials that incorporate these fabrics with resin systems. Think of IPC-4412 as defining the skeleton (glass reinforcement) and IPC-4101 as defining the complete body (glass plus resin as finished laminate). When ordering laminates per IPC-4101 slash sheets, the glass style per IPC-4412 is typically specified within the material construction.

Why does glass style matter for high-speed PCB design?

Glass style directly affects fiber weave effect, which causes intra-pair skew and impedance variations in high-speed differential pairs. Open weaves like 7628 create larger resin pockets where signal velocity differs significantly from glass-covered regions. At data rates above 10 Gbps, this skew can cause eye closure and bit errors. Tighter weaves (1080, 2116) or spread glass fabrics minimize these effects by creating more uniform dielectric distribution.

Can I specify glass style when ordering PCBs?

Yes, you can and should specify glass style for critical applications. Most fabricators accommodate glass style requests, though it may affect cost and lead time. For high-speed designs, specify glass style in your fabrication notes or stackup documentation. For standard designs, you can leave glass selection to the fabricator, who will optimize for cost and availability.

What is the difference between 1080 and 2116 prepreg?

Style 1080 uses finer yarns (ECD 450) creating thinner fabric (0.064 mm) with higher resin content (~60%). Style 2116 uses heavier yarns (ECE 225) creating thicker fabric (0.097 mm) with moderate resin content (~50%). Use 1080 when you need thinner dielectric layers or smoother surfaces; use 2116 when you need more thickness per ply or better dimensional stability. Both are widely available and cost-effective.

How do I know which glass style my fabricator uses?

Request the stackup documentation from your fabricator, which should list glass styles for each prepreg and core layer. If not specified, ask directly. For IPC-6012 Class 3 boards or aerospace applications, glass style traceability is typically required and documented in the fabrication data package. For commercial designs, you may need to specifically request this information.

Conclusion

IPC-4412 might seem like a behind-the-scenes specification, but it directly impacts every PCB’s performance and manufacturability. Understanding glass fabric styles helps you:

• Make informed material selections for your designs
• Communicate effectively with fabricators
• Troubleshoot signal integrity issues related to fiber weave effect
• Optimize cost without sacrificing quality

The key takeaways:

• IPC-4412C is the current standard for woven E-glass PCB fabrics
• Glass yarn nomenclature (ECG, ECD, ECE) indicates filament diameter and weight
• Common styles (106, 1080, 2116, 7628) offer different thickness and performance trade-offs
• Tighter weaves reduce fiber weave effect for high-speed designs
• Heavier fabrics offer cost advantages but can impact drilling and signal integrity

For most designs, your fabricator’s default glass selection works fine. But for high-speed, high-reliability, or cost-sensitive applications, specifying the right glass fabric per IPC-4412 gives you control over a critical material parameter.

This guide is intended for educational purposes. Always refer to the official IPC-4412C standard for authoritative requirements. Material specifications may vary by supplier and should be verified with your laminate manufacturer.