Prepreg Layer: Thickness Range 0.05-0.20 mm

Component Specifications

Definition

Prepreg (pre-impregnated) layer is a composite material consisting of fiberglass fabric impregnated with partially cured epoxy resin (B-stage). In HDI PCB manufacturing, it serves as the dielectric insulating layer between copper layers, providing electrical insulation, mechanical support, and thermal stability. During lamination under heat and pressure, the resin fully cures (C-stage), bonding adjacent copper layers and core materials to form a multilayer PCB structure.

Working Principle

The prepreg layer functions through thermosetting polymerization. During PCB lamination, heat (typically 180-200°C) and pressure (200-400 psi) cause the partially cured epoxy resin to flow, fill gaps, and fully cross-link, creating permanent bonds between copper layers and core materials while providing dielectric insulation with controlled thickness and electrical properties.

Materials

Fiberglass fabric (E-glass, 106-1080 style) impregnated with epoxy resin (FR-4 grade, tetrafunctional or multifunctional), typically with flame retardant additives (brominated compounds) to meet UL94 V-0 standards. Resin content: 45-65%, gel time: 90-180 seconds at 171°C.

Technical Parameters

Parameter	Typical range	Notes & selection driver
Gel Time	120-150 seconds @ 171°C
Resin Content	50-60%
Flow Percentage	25-40%
Thickness Range	0.05-0.20 mm
Dissipation Factor (Df)	0.015-0.025 @ 1 MHz
Dielectric Constant (Dk)	3.8-4.5 @ 1 MHz
Glass Transition Temperature (Tg)	140-180°C
Thermal Decomposition Temperature (Td)	>300°C

Ranges are indicative industry figures for RFQ preparation, not a supplier commitment. Confirm every value and standard with the legal manufacturer before ordering.

Standards

IPC-4101, IPC-4103, IEC 61249-2, UL 94

Parent Products

This component is used in the following industrial products

HDI PCB

A printed circuit board with high wiring density per unit area, featuring microvias, fine lines, and multiple sequential lamination layers.

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Engineering Analysis

Risks & Mitigation

Delamination under thermal stress
Resin starvation causing voids
Inconsistent dielectric properties
Moisture absorption affecting performance
Incomplete cure leading to reliability issues

FMEA Triads

Trigger: Insufficient resin flow during lamination
Failure: Voids and poor interlayer bonding
Mitigation: Optimize lamination pressure/temperature profiles and ensure proper resin content specifications

Trigger: Moisture absorption before lamination
Failure: Void formation and delamination during reflow
Mitigation: Proper storage in controlled humidity environments and pre-baking before use

Trigger: Inconsistent resin distribution
Failure: Variable dielectric properties across PCB
Mitigation: Implement statistical process control on resin content and uniformity measurements

Industrial Ecosystem

Compatible With

Typical Suppliers & Equivalents

Compliance & Inspection

Tolerance

Thickness tolerance: ±10%, Dielectric constant tolerance: ±0.2

Test Method

IPC-TM-650 test methods for dielectric properties, thermal analysis (DSC/TGA), and mechanical testing per IPC-4101 specifications

Procurement Evaluation Criteria

A practical evidence checklist for RFQ preparation and supplier evaluation.

Technical documentation

Request current drawings, revision history, and a signed specification sheet.

Manufacturing capability

Verify equipment lists, process limits, capacity, and representative production evidence.

Inspection readiness

Confirm test methods, calibrated equipment, sampling plans, and traceable reports.

Supplier transparency

Check the legal entity, factory address, ownership, certifications, and direct contacts.

CNFX does not score or rank suppliers. Buyers must verify all claims and documents with the legal manufacturer before ordering.

Manufacturers of Prepreg Layer

Manufacturer profiles associated with Prepreg Layer.

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Compiled and source-reviewed by the CNFX editorial team. Each manufacturer above links to the page on that company's own website where the product is listed, with the date we checked it. How we source and review

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Frequently Asked Questions

What is the difference between prepreg and core material in PCBs?

Core material is fully cured (C-stage) copper-clad laminate with copper on both sides, while prepreg is partially cured (B-stage) dielectric material without copper that bonds cores together during lamination.

How does prepreg thickness affect PCB performance?

Prepreg thickness determines interlayer dielectric spacing, affecting impedance control, signal integrity, and thermal management. Thinner prepreg enables higher density interconnections in HDI designs.

What happens if prepreg resin content is too low?

Insufficient resin content can cause resin starvation, leading to poor bonding, delamination risks, and reduced dielectric properties due to incomplete coverage of fiberglass weave.

Data Basis

Editorial classification, named public sources where available, and source-reviewed manufacturer records. See the editorial policy.

Preliminary Technical Classification

This page supports structured research, RFQ preparation, and supplier evaluation. It does not replace buyer-led supplier qualification, standards review, or technical approval.

Prepreg Layer