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A Comprehensive Guide to Display Cover Glass

From Materials and Manufacturing Processes to Functional Coatings and Future Trends

I. Overview of Cover Glass: Definition and Core Value

1. What Is Display Cover Glass?

Display cover glass is the transparent protective layer positioned on the outermost surface of display devices such as smartphones, tablets, industrial monitors, automotive displays, and self-service terminals.

Core Materials

High-strength glass (mainstream choice)
Specialized transparent polymers (for lightweight or flexible applications)

2. Core Functions and Value of Cover Glass

Cover glass is far more than a simple protective layer—it is a critical carrier of functionality, performance, and user experience:

Physical Protection
Protects the underlying touch panel (TP) and display module (LCD / OLED) from scratches, impacts, and daily wear
Touch Interface
Provides a smooth, responsive, and stable surface for touch interaction
Optical Window
Ensures high light transmittance and low reflectance for accurate colors, sharp images, and clear visibility
Design Platform
Supports 2.5D / 3D curved edges, decorative silk printing, anti-glare, and anti-fingerprint functional designs

II. Manufacturing Foundation: The Origin of Cover Glass

1. Glass Substrate — Formation of the “Raw Glass Sheet”

The starting point of cover glass manufacturing is unstrengthened, unprocessed glass sheets, commonly referred to in the industry as raw glass.

Primary Raw Materials

Silica sand (SiO₂, main component)
Soda ash (Na₂CO₃)
Limestone (CaCO₃)
Feldspar and other auxiliary materials

Basic Manufacturing Process
Raw material batching → High-temperature melting (>1500°C) → Homogenization and fining → Forming → Annealing and cooling

2. Comparison of Two Mainstream Glass Forming Technologies

Aspect	Float Process	Overflow Down-Draw Process
Principle	Molten glass floats on molten tin and forms under gravity and surface tension	Molten glass flows down from both sides of an overflow trough and fuses at the bottom
Surface Condition	One side contacts tin, the other contacts atmosphere	Both sides are pristine surfaces with no contact
Key Features	Lower cost, good flatness, widely used	Exceptional purity, flatness, and mechanical strength
Typical Applications	Mid-range and general-purpose cover glass	High-end consumer electronics, industrial and automotive cover glass
Representative Manufacturers	AGC, NSG, CSG, Xinyi	Corning (Gorilla Glass), SCHOTT

Conclusion
The overflow down-draw process is the preferred choice for high-end cover glass applications.

III. From Raw Glass to Finished Cover Glass: Key Processing Steps

Overall Manufacturing Flow

Raw glass → CNC machining → Pre-grinding → Cleaning → Chemical strengthening → Post-grinding → Post-processing (silk printing / coating) → Inspection and packaging

1. CNC Shape Machining

Purpose

Precisely cut the final outline and dimensions
Create openings for speakers, cameras, buttons, and sensors

Equipment

High-precision CNC machines
Diamond cutting tools

2. Grinding and Polishing Processes

Purpose

Precisely control glass thickness
Improve surface flatness and smoothness
Eliminate cutting marks, micro-cracks, and residual stress

Process Types

Pre-grinding: thickness control before strengthening
Post-grinding: contour refinement after strengthening

3. Core Process: Chemical Strengthening

Principle
The glass is immersed in molten potassium nitrate (KNO₃) at high temperature, allowing sodium ions (Na⁺) in the glass surface to be replaced by potassium ions (K⁺).

Strengthening Effects

Larger K⁺ ions are forced into the glass surface
A strong surface compressive stress layer (CS) is formed
A corresponding internal tensile stress layer develops
Overall glass strength increases by several times to dozens of times

Key Parameters

Surface compressive stress (CS)
Depth of layer (DOL)

4. Cleaning, Silk Printing, and Post-Processing

Ultrasonic cleaning and drying: removes particles, oils, and ionic residues
Silk printing and decoration:
- Light blocking
- Concealment of internal structures
- Enhanced aesthetic appearance

IV. Functional Surface Coating Technologies

1. AG (Anti-Glare)

Problem Addressed: Severe screen glare under strong ambient light
Principle: Micro-textured surface converts specular reflection into diffuse reflection
User Benefit: Clear readability even in outdoor or high-light environments

2. AR (Anti-Reflection / Anti-Reflective)

Problem Addressed: Reflection reduces contrast and color saturation
Principle: Optical interference coatings cancel reflected light waves
User Benefit: Higher contrast, richer colors, and a “glass-free” visual experience

3. AF (Anti-Fingerprint)

Problem Addressed: Fingerprints and oil residue accumulation
Principle: Fluorinated nano-scale hydrophobic and oleophobic coating (lotus effect)
User Benefit: Smoother touch, easier cleaning, and improved durability

Industry Trend
AR + AF composite coatings have become standard in mid-to-high-end devices.

V. Reliability Validation: Ball Drop Impact Test

1. Test Method

A steel ball of specified material and mass is dropped freely from a fixed height onto designated positions of the cover glass (center or weakest area).

2. Impact Energy Calculation

Formula

\times g \times h

E: Impact energy (J)
m: Mass of the steel ball (kg)
g: Gravitational acceleration (9.8 m/s²)
h: Drop height (m)

3. Acceptance Criteria

No cracks or breakage after testing
Or crack length within specified limits
Requirements vary by application (consumer, industrial, automotive)

VI. Technology Trends and Future Evolution

1. Evolution of Cover Glass Form Factors

2D flat → 2.5D curved edge → 3D curved glass → Foldable UTG (Ultra-Thin Glass)

2. New Material Directions

Glass-Ceramics: Significantly higher hardness and toughness, offering major improvements in drop resistance
Sapphire Glass: Exceptional scratch resistance, but higher cost and weight, mainly used in camera covers and high-end watches

3. Industry Challenges and Future Outlook

Challenges

Achieving thinner, lighter, and more curved designs while maintaining or enhancing strength

Future Trends

Deep integration with display technologies (under-display cameras, Micro-LED)
Integration of sensing functions (fingerprint recognition, pressure sensing)
Cover glass is evolving from a protective component into an intelligent interaction platform