Overview
IEC TR 63091:2017 - "Study for the derating curve of surface mount fixed resistors – Derating curves based on terminal part temperature" is an IEC technical report that analyzes power derating for surface-mount device (SMD) fixed resistors. The report is applicable to SMB resistors with sizes equal to or smaller than RR6332M and covers typical rectangular and cylindrical SMD resistors referenced in IEC 60115-8. Rather than using ambient temperature alone, IEC TR 63091 investigates derating curves tied to the terminal part temperature and provides measurement methods, thermal resistance data, and guidance for establishing practical derating limits.
Key topics and technical requirements
- Derating approach: Comparison of existing ambient-temperature based derating curves with the proposed terminal part temperature–based derating curves and rationale for the change.
- Temperature measurement methods: Detailed procedures for measuring terminal part temperature using thermocouples and infrared thermographs, including attachment, wiring, spatial resolution and error considerations (Annexes G, I).
- Thermal resistance and heat paths: Measurement and definitions of thermal resistance from terminal to surface hotspot (R_th shs-t), plus methods used by resistor manufacturers (Annexes F, H).
- Test setups and environmental effects: Influence of printed circuit board (PCB) layout, number of mounted resistors, airflow/wind speed in test chambers, and board thermal properties on temperature rise (Annexes B, C, D, K).
- Practical guidance: Recommended measurement systems, calculation of measurement error, and suggestions for applying terminal-temperature derating curves in product design (Sections 4, Annex E).
- Terminology & scope: Terms, normative references and applicability to SMB-size SMD resistors (Sections 1–3).
Practical applications
- Establishing power derating limits for SMD resistors in high-reliability electronics.
- Validating resistor operating temperature for PCB designers, component engineers, and reliability engineers to prevent overheating and premature failure.
- Designing thermal test protocols in component and test laboratories to measure terminal temperatures and thermal resistance accurately.
- Informing resistor manufacturers on test-board configurations and reporting practices for datasheets and customer guidance.
Who should use this standard
- Resistor manufacturers and test laboratories
- Electronic component engineers and designers
- PCB/layout engineers concerned with thermal management
- Reliability and quality assurance teams
- Standards developers and consultants working with passive component qualification
Related standards
- IEC 60115-8 (referenced for resistor types and sizes)
- Relevant IEC test-method and component reliability standards for passive components
Keywords: IEC TR 63091:2017, derating curve, surface mount fixed resistors, terminal part temperature, SMD resistors, thermal resistance, thermocouple, infrared thermograph, power derating, PCB heat dissipation.