ISO/TS 25336:2025

Plastics - Thermosetting resin-based materials - Low-temperature cracking index test by embedded metal block method

This document defines a method for testing the low-temperature cracking index of thermosetting resin-based materials. The test method described in this document is suitable for quantifying and comparing the low-temperature cracking of thermosetting resin-based materials in laboratory settings. This document does not refer to thermosetting resin-based materials that can also crack at 0 °C and above.

Plastiques — Matériaux à base de résines thermodurcissables — Essai d'indice de fissuration à basse température par la méthode du bloc métallique

General Information

• Status: Published
• Publication Date: 23-Oct-2025
• ICS: 83.080.10 - Thermosetting materials
• Technical Committee: ISO/TC 61/SC 12 - Thermosetting materials
• Drafting Committee: ISO/TC 61/SC 12/WG 5 - Unsaturated polyesters, epoxy resins and other resins
• Current Stage: 6060 - International Standard published
• Start Date: 24-Oct-2025
• Due Date: 14-Feb-2028
• Completion Date: 24-Oct-2025

Overview

ISO/TS 25336:2025 - Plastics - Thermosetting resin-based materials - Low-temperature cracking index test by embedded metal block method provides a laboratory method to quantify and compare the low-temperature cracking behavior of thermosetting resin-based materials. The Technical Specification establishes the embedded metal block method, describes recommended mould and stress module designs, specimen preparation (casting, degassing, curing), and a procedure to determine the critical cracking temperature and calculate a low-temperature cracking index (CR). The document is intended for materials that crack below 0 °C and is applicable in screening and validation of encapsulation materials such as epoxy resins used in electronics.

Key topics and technical requirements

• Test principle: Simulates encapsulation stress by pre-embedding a metal stress module and cooling the specimen to identify the cracking temperature and calculate CR.
• Apparatus and environmental controls:
  • Temperature chambers down to −70 °C with controlled ramp rate 0.1–0.3 °C/min.
  • Vacuum equipment (degassing and batching) capable of at least 100 Pa.
  • Drying/curing ovens with appropriate temperature/time control.
• Mould and stress module design:
  • Specified metal mould components (e.g., 35CrMo7 or P20), plate thickness and surface roughness (Ra1.6), cavity and casting gate geometry, and stress module dimensions and chamfer radius as described in the specification.
• Specimen preparation:
  • Preheating mould (example: 100 °C for ≥2 h), preparing thermosetting resin-based compounds with fillers/curing agents, vacuum stirring/degassing, casting (including APG or vacuum casting), vacuum degassing (100–300 Pa for 30 min), and curing per product specification.
• Inspection and reporting:
  • Visual or instrumented crack detection, checking for porosity/gaps, and documenting test conditions and CR calculation.

Applications and who uses this standard

• Primary users: power electronics manufacturers, materials R&D teams, test laboratories, and quality assurance engineers evaluating encapsulants and potting compounds.
• Practical applications:
  • Screening and comparison of thermosetting encapsulation materials (epoxies, resin systems) for low-temperature brittleness.
  • Supporting material selection for automotive, aerospace, and industrial electronics exposed to cold environments.
  • R&D benchmarking to improve crack resistance and reliability of encapsulated devices.

Related standards

• ISO 472 - Plastics - Vocabulary (normative reference included in ISO/TS 25336:2025).
• ISO/TC 61 / SC 12 - Technical committee and subcommittee responsible for thermosetting materials.

Keywords: ISO/TS 25336:2025, low-temperature cracking index, embedded metal block method, thermosetting resin-based materials, epoxy resins, encapsulation, low-temperature testing, vacuum degassing, mould design.

Standards Content (Sample)

Technical
Specification
ISO/TS 25336
First edition
Plastics — Thermosetting
2025-10
resin-based materials — Low-
temperature cracking index test by
embedded metal block method
Plastiques — Matériaux à base de résines thermodurcissables —
Essai d'indice de fissuration à basse température par la méthode
du bloc métallique
Reference number
© ISO 2025
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
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Phone: [phone]
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Published in Switzerland
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Apparatus . 2
5 Test method . 2
5.1 mould and stress module .2
5.1.1 mould .2
5.1.2 Stress module .3
5.1.3 Assembly of mould .4
5.2 Specimen preparation .5
5.2.1 Preheat .5
5.2.2 Make thermosetting resin base compound .5
5.2.3 Casting thermosetting resin-based condensate . .6
5.2.4 Vacuum degassing .6
5.2.5 Curing .6
5.2.6 Demoulding and treatment .7
5.3 Test procedures .7
5.3.1 Preliminary test .7
5.3.2 Cracking temperature test .7
6 Low-temperature cracking index calculation . 8
7 Test report . 8
Bibliography .10

iii
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
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has been established has the right to be represented on that committee. International organizations,
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The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO document should be noted. This document was drafted in accordance with the editorial rules of the
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related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 61, Plastics, Subcommittee SC 12, Thermosetting
materials.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.

iv
Introduction
With the advancement of large-scale integration of integrated circuits and miniaturization of electronic
components, thermosetting resin-based materials have been increasingly adopted in power electronics
device encapsulation. However, their low-temperature brittleness can lead to encapsulation cracking
failures.
This document introduces the embedded metal block method, and the corresponding moulds, stress module
and sample preparation are also recommended. The method simulates encapsulation structures by pre-
embedding stress modules in test specimens and determines the critical temperature for material cracking
through thermal testing. A quantitative evaluation methodology, the low-temperature cracking index (CR),
is established accordingly. This method has been applied by power electronics manufacturers for screening
and validation of encapsulation materials such as epoxy resins.
This document facilitates innovation in material research and development and enhances the reliability of
electronic devices.
v
Technical Specification ISO/TS 25336:2025(en)
Plastics — Thermosetting resin-based materials — Low-
temperature cracking index test by embedded metal
block method
1 Scope
This document defines a method for testing the low-temperature cracking index of thermosetting resin-
based materials.
The test method described in this document is suitable for quantifying and comparing the low-temperature
cracking of thermosetting resin-based materials in laboratory settings.
This document does not refer to thermosetting resin-based materials that can also crack at 0 °C and above.
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.
ISO 472, Plastics — Vocabulary
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 472 and the following apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
thermosetting resin-based compound
liquid or semi-solid compound for pouring power electronic equipment comprising at least a thermosetting
resin and a curing agent, and optionally one or more of the additives such as fillers, tougheners, accelerators, etc.
3.2
thermosetting resin-based condensate
product formed by cu
...