IEC 61249-3-6:2026

Materials for circuit boards and other interconnecting structures - Part 3-6: Sectional specification set for unreinforced base materials clad and unclad - Polytetrafluoroethylene (PTFE) filled laminate sheets of defined flammability (vertical burning test), copper-clad

IEC 61249-3-6:2026 specifies requirements for properties of polytetrafluoroethylene (PTFE) filled unreinforced laminated sheet of a thickness 0,02 mm up to 3,2 mm, of defined flammability (vertical burning test), copper-clad.
This document is applicable to the design, manufacture, use of PTFE filled unreinforced laminated sheet of defined flammability (vertical burning test), copper-clad.
Its flame resistance is defined in terms of the flammability requirements of 8.3.

Matériaux pour circuits imprimés et autres structures d’interconnexion - Partie 3-6: Collection de spécifications intermédiaires pour matériaux de base non renforcés, métallisés et non métallisés - Feuilles stratifiées en PTFE avec charges d’inflammabilité définie (essai de combustion verticale), plaquées cuivre

General Information

• Status: Published
• Publication Date: 18-May-2026
• ICS: 31.180 - Printed circuits and boards
• Technical Committee: TC 91 - Electronics assembly technology
• Drafting Committee: WG 4 - TC 91/WG 4
• Current Stage: PPUB - Publication issued
• Start Date: 19-May-2026
• Completion Date: 19-Jun-2026

Overview

IEC 61249-3-6:2026 is an international standard developed by the International Electrotechnical Commission (IEC) for materials used in circuit boards and other interconnecting structures. This document sets out the requirements for unreinforced base materials consisting of polytetrafluoroethylene (PTFE) filled laminate sheets of defined flammability (as determined by the vertical burning test) that are copper-clad. Applicable to PTFE filled unreinforced laminated sheets with thicknesses from 0.02 mm to 3.2 mm, the standard addresses the needs of designers, manufacturers, and users of printed circuit boards (PCBs) requiring high-performance flame-resistant materials.

Key aspects such as construction, material properties, electrical performance, mechanical tolerances, and conformity assessment are covered, ensuring consistency and safety in the application of these specialized laminates.

Key Topics

• Material Composition

  • PTFE or modified PTFE as base resin
  • Inorganic fillers (e.g., silicon dioxide, titanium dioxide, aluminium oxide, boron nitride) may be used
  • Copper-clad layers as per IEC 61249-5-1
  • No reinforcement (unreinforced base materials)

• Flammability Requirements

  • Defined by a vertical burning test according to IEC 61189-2
  • V-0 flammability (default unless otherwise specified)
  • Resist dripping and burning after flame application, ensuring the highest safety within electronic assemblies

• Electrical and Mechanical Properties

  • Surface and volume resistivity
  • Relative permittivity and dissipation factor
  • Electric strength, arc resistance, and dielectric breakdown
  • Peel strength of copper foil
  • Dimensional stability, thickness, and tolerance
  • Thermal properties such as decomposition temperature, Z-axis and X/Y-axis coefficient of thermal expansion

• Appearance and Quality Control

  • Visual inspection parameters for copper-clad and unclad faces
  • Permissible defect levels for indentations, scratches, wrinkles, and raised areas
  • Inspection and qualification procedures as defined in the standard

Applications

Materials that comply with IEC 61249-3-6:2026 are primarily used in the fabrication of printed circuit boards (PCBs) and other interconnecting structures in advanced electronics. The unique properties of PTFE-based copper-clad laminates make them well-suited for:

• High-frequency and RF electronic circuits
  PTFE laminates offer low dielectric loss and stable electrical properties at microwave frequencies, making them ideal for RF PCBs used in telecom, aerospace, and defense industries.

• Environments Requiring Enhanced Flame Resistance
  Ensuring compliance with strict flammability criteria is vital for power electronics, industrial controls, and safety-critical systems.

• Precision Electronic Applications
  The dimensional stability and defined tolerances support high-density interconnections and multilayer PCB construction.

• Custom and High-Performance PCBs
  As customization is supported (by agreement between user and supplier), this standard addresses specialized industry needs where specific performance or safety attributes are required.

Related Standards

• IEC 61189-2 Series: These documents detail the test methods for electrical materials, including those used for flammability, resistivity, and mechanical properties.
• IEC 61249-5-1: Specifies requirements for copper foils used in copper-clad laminates.
• ISO 11014: Pertains to the safety data sheets for chemical products, relevant for safe handling and material safety compliance.
• IPC-TM-650: Includes test methods widely referenced in PCB industry for measuring dielectric properties.

Practical Value

Adopting IEC 61249-3-6:2026 helps manufacturers, designers, and end-users to:

• Select high-quality, flame-resistant PTFE laminate materials for PCBs
• Comply with international requirements for electrical and flammability performance
• Facilitate quality control, procurement, and inspection processes
• Achieve safety and reliability in electronic device manufacturing

For more information or to obtain the standard, visit the IEC webstore.

Standards Content (Sample)

IEC 61249-3-6 ®
Edition 1.0 2026-05
INTERNATIONAL
STANDARD
Materials for circuit boards and other interconnecting structures -
Part 3-6: Sectional specification set for unreinforced base materials clad and
unclad - Polytetrafluoroethylene (PTFE) filled laminate sheets of defined
flammability (vertical burning test), copper-clad
ICS 31.180  ISBN 978-2-8327-1248-1

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CONTENTS
FOREWORD . 3
1 Scope . 5
2 Normative references . 5
3 Terms, definitions and abbreviated terms . 6
3.1 Terms and definitions. 6
3.2 Abbreviated terms . 6
4 Construction and materials . 6
4.1 Construction . 6
4.2 Resin system . 6
4.3 Filler . 6
4.4 Metal foil . 6
4.5 Reinforcement . 6
5 Internal marking . 6
6 Electrical properties . 6
7 Non-electrical properties of the base material . 7
7.1 Appearance of the copper-clad sheet . 7
7.1.1 General . 7
7.1.2 Indentations (pits and dents) . 7
7.1.3 Wrinkles . 8
7.1.4 Scratches . 8
7.1.5 Raised areas . 8
7.2 Appearance of the unclad face . 8
7.3 Laminate thickness . 9
7.4 Bow and twist . 9
7.5 Properties related to the copper foil bond . 9
7.6 Heat shock . 10
7.7 Machining . 10
7.8 Dimensional stability . 10
7.9 Sheet sizes and tolerances . 11
7.9.1 Typical sheet sizes . 11
7.9.2 Tolerances for sheet sizes . 11
7.10 Cut panels sizes, tolerances and rectangularity . 11
7.10.1 Cut panel sizes . 11
7.10.2 Size tolerances for cut panels . 11
7.10.3 Rectangularity of cut panels . 11
8 Non-electrical properties of the base material after complete removal of the
copper foil . 12
8.1 General . 12
8.2 Appearance of the dielectric base material . 12
8.3 Flammability . 12
8.4 Water absorption . 13
8.5 Glass transition temperature and cure factor . 13
8.6 Decomposition temperature . 13
8.7 Z-axis CTE . 13
8.8 X/Y-axis CTE . 13
8.9 Thermal conductivity . 14
9 Quality assurance . 14
9.1 Quality system . 14
9.2 Responsibility for inspection . 14
9.3 Qualification inspection . 14
9.3.1 General . 14
9.3.2 Samples . 14
9.3.3 Frequency . 14
9.3.4 Criterion rule . 14
9.4 Quality conformance inspection . 15
9.4.1 General . 15
9.4.2 Inspection lot . 15
9.4.3 Group A inspection . 15
9.4.4 Group B inspection . 15
9.4.5 Group C inspection . 16
9.4.6 Criterion rule . 16
9.4.7 Rejected lots . 16
9.5 Certificate of conformance . 16
9.6 Safety data sheet . 16
10 Packaging and marking . 16
11 Ordering information . 17
Annex A (informative) Engineering information . 18
A.1 General . 18
A.2 Electrical properties . 18
A.3 Non-electrical properties of the base material after complete removal of the
copper foil . 18
Bibliography . 19

Table 1 – Electrical properties . 7
Table 2 – Indentations . 8
Table 3 – Nominal thickness and tolerance of metal-clad laminate . 9
Table 4 – Bow and twist requirements . 9
Table 5 – Peel strength requirements . 10
Table 6 – Heat shock requirements . 10
Table 7 – Dimensional stability . 10
Table 8 – Size tolerances for cut panels . 11
Table 9 – Rectangularity of cut panels . 11
Table 10 – Flammability requirements . 12
Table 11 – Water absorption requirements . 13
Table 12 – Decomposition temperature requirements . 13
Table 13 – Z-axis CTE requirements . 13
Table 14 – X/Y-axis CTE requirements . 13
Table 15 – Qualification and conformance inspection . 14

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
Materials for circuit boards and other interconnecting structures -
Part 3-6: Sectional specification set for unreinforced base materials clad
and unclad - Polytetrafluoroethylene (PTFE) filled laminate sheets of
defined flammability (vertical burning test), copper-clad

FOREWORD
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shall not be held responsible for identifying any or all such patent rights.
IEC 61249-3-6 has been prepared by IEC technical committee 91: Electronics assembly
technology. It is an International Standard.
The text of this International Standard is based on the following documents:
Draft Report on voting
91/2102/FDIS 91/2110/RVD
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/publications.
A list of all parts in the IEC 61249 series, published under the general title Materials for circuit
boards and other interconnecting structures, can be found on the IEC website.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
– reconfirmed,
– withdrawn, or
– revised.
1 Scope
This part of IEC 61249 specifies requirements for properties of polytetrafluoroethylene (PTFE)
filled unreinforced laminated sheet of a thickness 0,02 mm up to 3,2 mm, of defined flammability
(vertical burning test), copper-clad.
This document is applicable to the design, manufacture, use of PTFE filled unreinforced
laminated sheet of defined flammability (vertical burning test), copper-clad.
Its flame resistance is defined in terms of the flammability requirements of 8.3.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies.
For undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 61189-2, Test methods for electrical materials, printed boards and other interconnection
structures and assemblies - Part 2: Test methods for materials for interconnection structures
IEC 61189-2-721, Test methods for electrical materials, printed board and other interconnection
structures and assemblies - Part 2-721: Test methods for materials for interconnection
structures - Measurement of relative permittivity and loss tangent for copper clad laminate at
microwave frequency using split post dielectric resonator
IEC 61189-2-803, Test methods for electrical materials, printed board and other interconnection
structures and assemblies - Part 2-803: Test methods for Z-axis expansion of base materials
and printed boards
IEC 61189-2-805, Test methods for electrical materials, printed boards and other
interconnection structures and assemblies - Part 2-805: X/Y CTE test for thin base materials by
TMA
IEC 61189-2-807, Test methods for electrical materials, printed board and other interconnection
structures and assemblies - Part 2-807: Test methods for materials for interconnection
structures - Decomposition temperature (T ) using TGA
d
IEC 61249-5-1, Materials for interconnection structures - Part 5: Sectional specification set for
conductive foils and films with or without coatings - Section 1: Copper foils (for the manufacture
of copper-clad base materials)
ISO 11014, Safety data sheet for chemical products - Content and order of sections
IPC-TM-650 TM 2.5.5.5, Stripline Test for Permittivity and Loss Tangent (Dielectric Constant
and Dissipation Factor) at X-Band
3 Terms, definitions and abbreviated terms
3.1 Terms and definitions
No terms and definitions are listed in this document.
ISO and IEC maintain terminology databases for use in standardization at the following
addresses:
– IEC Electropedia: available at https://www.electropedia.org/
– ISO Online browsing platform: available at https://www.iso.org/obp
3.2 Abbreviated terms
CTE Coefficient of thermal expansion
PTFE Polytetrafluoroethylene
4 Construction and materials
4.1 Construction
The sheet consists of an insulating base made of PTFE or modified PTFE as the primary resin,
with metal-foil bonded to one side or both.
4.2 Resin system
PTFE resin or modified PTFE as the primary resin, with a filler addition.
4.3 Filler
Typical filling (filler) materials can be silicon dioxide, titanium dioxide, aluminium oxide, boron
nitride, chopped fiber, hollow sphere. It is possible to use other or additional filling material to
achieve a specific characteristic.
4.4 Metal foil
Copper, as specified in IEC 61249-5-1, copper foil (for the manufacture of copper-clad
materials). The preferred foils are electrodeposited of defined ductility.
4.5 Reinforcement
No reinforcement.
5 Internal marking
Shall be as agreed upon between user and supplier.
6 Electrical properties
The electrical properties requirements are shown in Table 1. For some typical values, see
Annex A.
Table 1 – Electrical properties
Property Test method Units Requirement
Surface resistivity after damp heat
IEC 61189-2 2E04 MΩ ≥ 10 000
while in the humidity chamber
Volume resistivity after damp heat
IEC 61189-2 2E04 MΩ·m ≥ 5 000
while in the humidity chamber
Surface resistivity after E-24/125
IEC 61189
...