Overview
IEC 60539-2:2019 is the IEC sectional specification for surface mount directly heated negative temperature coefficient (NTC) thermistors. It applies to surface-mount NTC thermistors typically made from transition metal oxide semiconducting materials, with metallized connecting pads or soldering strips designed to be mounted directly onto substrates for hybrid circuits or printed circuit boards (PCBs). This 2019 edition updates structure and harmonization with ISO/IEC Directives and IEC 60539-1:2016, and adds expanded category temperatures and an additional SMT dimension (0402M).
Keywords: IEC 60539-2:2019, surface mount NTC thermistors, SMT thermistors, SMD thermistors, negative temperature coefficient thermistors
Key topics and technical requirements
- Scope and definitions: Applicable component types, terms and required detail in purchaser/manufacturer specifications.
- Information for detail specification: Outline drawings, mounting instructions, rated characteristics, marking and coding requirements.
- Preferred ratings and characteristics: Tolerances on zero-power resistance and specified climatic categories for reliability.
- Quality assessment procedures: Requirements for primary manufacture, structurally similar components, qualification approval, and lot-by-lot quality conformance inspection.
- Comprehensive test and measurement procedures, including:
- Mounting, drying and recovery practices
- Visual examination and dimensional checks
- Electrical tests (zero-power resistance, B-value or resistance ratio, R–T characteristic)
- Thermal tests (dissipation factor, thermal time constant)
- Resistance to soldering heat and solderability
- Environmental endurance tests: rapid temperature change, thermal shock, damp heat (steady state and cyclic), and long-term endurance at category temperatures
- Mechanical and chemical resistance: shear (adhesion), substrate bending, solvent resistance (component and marking)
- Annexes: Normative guidance on dimension coding for surface-mount NTC thermistors (including new 0402M size) and detailed quality assessment procedures.
- Notable updates in 2019 edition:
- Structure revised per ISO/IEC Directives, Part 2:2016
- Added upper category temperatures: 175 °C, 200 °C, 250 °C, 315 °C, 400 °C
- Added 0402M dimension in Annex A
Practical applications and who uses this standard
IEC 60539-2:2019 is used by:
- Component manufacturers for design, production and qualification of SMT NTC thermistors
- Test laboratories and QA teams for type approval, lot inspection and reliability testing
- PCB assemblers and electronics manufacturers to verify soldering and mounting compatibility
- Design engineers specifying temperature-sensing or temperature-compensation components in consumer, industrial, automotive and hybrid circuit applications
- Procurement and compliance officers ensuring purchased thermistors meet international test and marking requirements
This standard helps ensure reliable thermal and electrical performance of surface-mount NTC thermistors across manufacturing, assembly and end-use environments.
Related standards
- IEC 60539-1:2016 - General specifications for directly heated NTC thermistors (harmonized with this Part 2)
- ISO/IEC Directives, Part 2:2016 - structural/format guidance used in the 2019 revision
Keywords: IEC standards, NTC thermistor testing, solderability testing, thermistor qualification, surface mount thermistors