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IEC 62715-1-1: Flexible Display Devices Terminology and Symbols
Key Insight: IEC 62715-1-1:2013, developed by IEC TC 110 (Electronic Display Devices), provides the foundational terminology and letter symbols for the rapidly evolving field of flexible display technology. As the first part of the IEC 62715 series, it establishes a common language for engineers, researchers, and manufacturers working with bendable, rollable, and foldable displays.
1. Scope and Importance of Terminology Standardization
Flexible display technology represents a fundamental shift from the rigid glass substrates that dominated display manufacturing for decades. By 2013, when this standard was published, flexible displays were transitioning from laboratory research to commercial products, creating an urgent need for standardized terminology. Without a common vocabulary, engineers from different companies and research groups could not reliably communicate specifications, compare performance, or establish consistent quality metrics.
The standard covers five categories of terms: general terms (defining what flexible displays are and their classifications), terms related to physical properties (describing mechanical and optical behavior under bending), terms related to constructive elements (specifying the structural components of flexible displays), terms related to performances and specifications (quantifying display quality and durability), and terms related to the production process (covering manufacturing methods).
Why Terminology Matters: Before IEC 62715-1-1, terms like “bending radius” and “flexibility” were used inconsistently across the industry. A display that one manufacturer called “flexible” might only be “bendable” under another’s classification. This standard eliminated that ambiguity, enabling precise technical communication across the global supply chain.
2. Key Terminology and Definitions
2.1 General Terms and Classification
The standard defines “flexible display device” as a flexible display panel and flexible module that are mechanically bendable in one or more of the steps of substrate handling, manufacturing, storage, use, operation, shipping, and relocation. Critically, the definition notes that flexible display devices are “generally rugged under rough handling.”
The classification system distinguishes between different degrees of flexibility. Table 1 summarizes the key flexible display categories implicitly recognized by the standard’s terminology framework.
| Term | Definition | Typical Bending Radius | Application Example |
|---|---|---|---|
| Bendable Display | Can be bent to a specific curvature, typically for installation or occasional use in curved form | 10-100 mm | Curved smartphones, automotive dashboard displays |
| Rollable Display | Can be rolled into a cylindrical form for storage or transport | 5-20 mm | Rollable TVs, portable large-format displays |
| Foldable Display | Can be folded along a defined crease line, typically with a specific hinge mechanism | 1-5 mm | Foldable smartphones, tablet hybrids |
| Conformable Display | Can comply to a curved surface without creasing, maintaining intimate contact with the underlying shape | Variable | Wearable devices, curved architectural displays |
2.2 Physical Property Terms and Letter Symbols
The standard assigns specific letter symbols to key physical properties of flexible displays. Table 2 shows the critical symbols that engineers use in specifications and design documents.
| Symbol | Quantity | Unit | Description |
|---|---|---|---|
| R | Bending radius | mm | Radius of curvature to which the display can be bent without damage |
| epsilon | Strain | % | Relative deformation of the display substrate under mechanical stress |
| sigma | Stress | Pa (or N/m2) | Mechanical stress applied to the display during bending |
| E | Young’s modulus | Pa | Elastic modulus of the display substrate material |
| N | Bending cycles | cycles | Number of bending operations the display withstands before failure |
| L0 | Original length | mm | Initial dimension of the display along the bending axis |
| Delta L | Elongation | mm | Change in length under tensile stress during bending |
Engineering Design Insight: The relationship between bending radius (R) and strain (epsilon) is fundamental to flexible display design: epsilon = t/(2R), where t is the total thickness of the display stack. This means that reducing the display thickness is the most direct path to achieving smaller bending radii. For a foldable display with R = 2 mm and a total stack thickness of 0.5 mm, the maximum strain in the outermost layer is approximately 12.5%, which constrains material choices significantly.
3. Constructive Elements and Production Process
The standard defines terminology for the key structural elements of flexible displays. These include: the flexible substrate (typically polyimide, PET, or ultra-thin glass), the barrier layer (protecting sensitive organic materials from moisture and oxygen permeation), the thin-film transistor (TFT) backplane, the light-emitting or light-modulating layer, the encapsulation layer, and optional touch sensor integration.
Production process terms cover methods such as roll-to-roll processing (R2R, where flexible substrates are processed on continuous rolls rather than discrete sheets), flexible printed circuit bonding, and laser lift-off (used to separate the flexible display from the rigid carrier glass used during manufacturing).
Critical Consideration: The standard notes that terms related to production processes are particularly important because flexible display manufacturing fundamentally differs from conventional rigid display fabrication. Roll-to-roll processing introduces web tension control, registration accuracy, and defect management challenges that do not exist in sheet-based processing. Standardized terminology for these processes enables clearer specification of manufacturing equipment and process conditions.
4. Engineering Design Insights
For engineers designing products incorporating flexible displays, IEC 62715-1-1 provides the conceptual framework needed to navigate this complex field. The separation of physical property terms from performance terms is particularly important: a display’s bending radius (physical property) determines the mechanical envelope, while its luminance uniformity after bending (performance) determines user experience. The standard’s letter symbol system enables unambiguous specification writing and cross-referencing between design documents.
The strain-bending radius relationship (epsilon = t/2R) has profound implications for stack-up design. Engineers must carefully select and arrange each layer — substrate, barrier, TFT, pixel, encapsulation, cover — to ensure that the neutral plane (where strain is zero) is positioned optimally. Placing brittle layers (e.g., transparent conductive oxides like ITO) at or near the neutral plane dramatically improves bending reliability.
Future-Proofing: While the IEC 62715-1-1 terminology was published in 2013, it was designed with extensibility for future flexible display technologies. Terms like “stretchable display” and “self-healing display” — which have become research topics since publication — can be accommodated within the standard’s framework without requiring fundamental restructuring of the terminology system.
5. Frequently Asked Questions
Q1: What is the difference between a “flexible” display and a “bendable” display according to IEC 62715-1-1?
A: “Flexible” is the broader category encompassing all displays that can be mechanically deformed. “Bendable” describes displays that can be bent to a specific curvature, typically for installation or periodic use. The key distinction is the degree of deformation and the intended use case.
A: “Flexible” is the broader category encompassing all displays that can be mechanically deformed. “Bendable” describes displays that can be bent to a specific curvature, typically for installation or periodic use. The key distinction is the degree of deformation and the intended use case.
Q2: Why does the standard include letter symbols for physical properties?
A: The letter symbol system ensures unambiguous communication in technical specifications, engineering drawings, and scientific publications. For example, specifying “R = 5 mm” is clear and universal, while writing “can be bent quite a lot” is subjective and unverifiable.
A: The letter symbol system ensures unambiguous communication in technical specifications, engineering drawings, and scientific publications. For example, specifying “R = 5 mm” is clear and universal, while writing “can be bent quite a lot” is subjective and unverifiable.
Q3: How does the standard handle emerging flexible display technologies that did not exist when it was published?
A: The terminology framework was designed with extensibility in mind. The five-term classification system (general, physical properties, constructive elements, performance, production process) can accommodate new technologies by adding terms to existing categories or creating subcategories as needed.
A: The terminology framework was designed with extensibility in mind. The five-term classification system (general, physical properties, constructive elements, performance, production process) can accommodate new technologies by adding terms to existing categories or creating subcategories as needed.
Q4: What role does IEC 62715-1-1 play in the broader IEC 62715 series?
A: It is the foundational terminology document. Subsequent parts of IEC 62715 address specific test methods (e.g., mechanical stress testing, environmental endurance, optical measurement) and application-specific requirements. All later parts reference the terminology and symbols established in Part 1-1.
A: It is the foundational terminology document. Subsequent parts of IEC 62715 address specific test methods (e.g., mechanical stress testing, environmental endurance, optical measurement) and application-specific requirements. All later parts reference the terminology and symbols established in Part 1-1.
