Directly heated negative temperature coefficient thermistors - Part 2: Sectional specification - Surface mount negative temperature coefficient thermistors (IEC 60539-2:2019); German version EN IEC 60539-2:2019
1Key Takeaways
This part of IEC 60539 is applicable to surface mount directly heated negative temperature coefficient thermistors, typically made from transition metal oxide materials with semiconducting properties.
2Expert Interpretation
A comprehensive interpretation of the DIN EN IEC 60539-2:2020 standard for surface mount negative temperature coefficient thermistors, covering technical specifications, test methods, quality assessment systems, and implementation key points, providing professional guidance for electronic component manufacturers and users.
Standard Overview and Technical Background
DIN EN IEC 60539-2:2020 is a specialized standard for surface mount negative temperature coefficient thermistors (NTC) published by the German Committee for Standardization (DKE) in December 2020. This standard replaces the previous version, DIN EN 60539-2, published in April 2011, with a transition period until August 23, 2022. This standard, part 2 of the IEC 60539 series, specifically addresses surface mount NTC thermistors.
The technical management unit for this standard is Subcommittee K 614, "Temperature and Voltage Dependent Resistors," of the DKE German Committee for Electrical, Electronic and Information Technology. This standard is fully consistent with the international standard IEC 60539-2:2019, demonstrating Germany's international coordination in the field of electronic component standardization.
Main technical changes and updates
Compared with the 2011 version of the standard, this revision includes the following important technical changes:
| Change items | 2011 version | 2020 version | Technical significance |
|---|---|---|---|
| Standard structure | Based on the old version of the directive | Compliant with ISO/IEC Directives, Part 2:2016 (7th Edition) | Enhanced standard coordination |
| Temperature category | Up to 155°C | Newly added 175°C, 200°C, 250°C, 315°C and 400°C | Expanded high temperature application range |
| Dimensions | 0402M not included | 0402M size added to Appendix A | Adapting to the trend of miniaturization |
| Harmonization | Independent requirements | Harmonized with IEC 60539-1:2016 | Improved the consistency of the standard system |
These changes reflect the electronics industry's increasing demand for high temperature performance and miniaturization of thermistors, especially the stringent requirements for component reliability in automotive electronics, industrial control and consumer electronics.
Scope of Application and Product Definition
This standard applies to directly heated surface-mount negative temperature coefficient thermistors, typically made from transition metal oxide semiconductor materials. These thermistors have metallized connections or pads and are designed for direct mounting on the substrate of a hybrid circuit or printed circuit board.
Key product features include:
- Surface mount technology (SMT) packaging
- Negative temperature coefficient (NTC) characteristics
- Based on transition metal oxide semiconductor materials
- Metallized electrode structure
Key Technical Parameters and Requirements
4.1 Zero-load Resistor Tolerance
The standard specifies preferred tolerance values for zero-load resistors: ±0.5%, ±1%, ±2%, ±3%, ±5%, and ±10%. These tolerance grades meet the resistance accuracy requirements of different application scenarios.
4.2 Climate Category
The standard provides a complete climate category classification system:
| Parameter Type | Optional Value | Application Area |
|---|---|---|
| Lower Category Temperature | -55°C, -40°C, -25°C, -10°C, -5°C, +5°C | Automotive Electronics, Outdoor Equipment |
| Upper Category Temperature | 70°C, 85°C, 100°C, 105°C, 125°C, 150°C, 155°C, 175°C, 200°C, 250°C, 315°C, 400°C | High Temperature Industrial Environment |
| Constant Damp Heat Duration | 21 days, 42 days, 56 days | Reliability Verification |
4.3 Dimensional Specifications
Appendix A specifies the size coding system for surface mount NTC thermistors, including the specific size requirements for common package sizes such as 0402M, 0603M, 1005M, 1608M, 2012M, 3216M, and 3225M.
Test Methods and Acceptance Criteria
7.1 Visual Inspection and Dimensional Inspection
The standard requires the use of a 10x magnifying glass for visual inspection, focusing on the following defects:
- The length of the ceramic crack does not exceed 25% of the L4 size
- The area of blistering on the glass package does not exceed 10% of the total area of a single side
- The area of metallization defects does not exceed 15% of the area of a single side
- The end face metallization peeling (leaching) does not exceed 25% of the relevant edge length
7.2 Electrical Performance Test
Includes verification of key electrical parameters such as zero-load resistance measurement, B value or resistance ratio determination, and resistance/temperature characteristic test.
7.3 Environmental Reliability Test
The standard specifies comprehensive environmental test items:
| Test Items | Test Criteria | Acceptance Criteria |
|---|---|---|
| Resistance to Soldering Heat | IEC 60068-2-58 | ΔR≤±5% |
| Solderability | IEC 60068-2-58 | Good Solder Coverage |
| Rapid Temperature Changes | IEC 60068-2-14 Na | ΔR≤±5% |
| Temperature shock | IEC 60068-2-14 Nc | ΔR≤±5% |
| Steady state damp heat | IEC 60068-2-78 Cab | ΔR≤±5% |
Quality assessment system
B.4 Quality consistency inspection
The standard establishes a complete quality assessment system, including:
- Initial manufacturing stage: The first component mixing process
- Structurally similar components: Grouping of components based on the same production process and size
- Type approval procedure: Fixed sample size inspection plan
- Batch inspection: Group A and Group B inspections
- Periodic inspection: Group C inspections
Inspection levels are selected according to IEC 61193-2 to ensure statistical validity.
Implementation Recommendations and Application Guidance
Manufacturing Process Control
Manufacturers should focus on the following process links:
- Strict control of material proportions and mixing processes
- Quality consistency of metallization processes
- Process optimization of welding heat resistance
- Process control of dimensional accuracy
Testing Laboratory Construction
It is recommended that the testing laboratory be equipped with the following equipment:
- 10x magnification visual inspection system
- High-precision resistance measurement equipment
- Environmental test chamber (temperature, humidity)
- Welding performance test equipment
- Mechanical reliability test equipment
Standard Conversion Implementation
For enterprises converting from the 2011 version to the 2020 version, it is recommended that:
- Complete the transition before August 23, 2022
- Update product specifications and technical documents
- Re-evaluate the temperature categories of high-temperature products
- Adjust quality control plans
Technology Development Trends and Outlook
As electronic equipment develops towards high temperature and high reliability, the technological development of surface mount NTC thermistors shows the following trends:
- Improved high-temperature performance: The addition of a 400°C upper temperature category meets the needs of automotive electronics and industrial applications
- Miniaturization: Support for smaller size specifications such as 0402M
- Increased reliability requirements: More stringent environmental testing conditions and acceptance criteria
- Standardization coordination: Further unification with international standards
This standard provides comprehensive technical specifications and quality assurance system for the design, manufacture and application of surface mount NTC thermistors, which is of great significance to promoting technological progress and improving product quality in the industry.