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.