Toughened Ceramic with Residual Compressive Stress

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Solution Overview

Problem

Conventional electronic device enclosures, such as housing and cover glass, are susceptible to damage from shock events like drops, leading to material defects like cracks and dents that weaken their protective capabilities.

Innovation Solution

A ceramic component is formed with a residual compressive stress by applying a dopant material with a lower coefficient of thermal expansion to the exterior surface of a ceramic substrate, diffusing it, and then cooling to generate compressive stress in the external portion, enhancing the material's toughness and resistance to damage.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional durable materials are used for enclosures, then protection against shock events is provided, but material defects like cracks and dents are formed that weaken the material strength

Engineering Contradiction:

Improveprotection capabilityVSAvoidmaterial strength

Core Design Contradiction:

ReliabilityVSStrength

Solution Approach 1:

The patent applies a surface treatment process that modifies the physical and chemical parameters of the ceramic surface layer. By controlling diffusion conditions (temperature, time, composition), the surface layer's microstructure is changed to create compressive stress, transforming the material properties to achieve both high strength and damage resistance

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent creates a composite structure with a treated surface layer and a bulk substrate. The surface layer has different properties (compressive stress, modified composition) than the bulk material, forming a composite system where each layer performs its specific function: the surface layer resists crack initiation and propagation while the bulk provides structural support

Inventive Principle:

Principle #40Composite materials

2Strength

If the enclosure material is made tougher to prevent defects, then resistance to shock damage is improved, but the material may become more complex to manufacture

Engineering Contradiction:

ImprovetoughnessVSAvoidmanufacturing simplicity

Core Design Contradiction:

StrengthVSEase of manufacture

Solution Approach 1:

The patent utilizes thermal expansion differences between the surface layer and bulk substrate. During cooling after heat treatment, the surface layer contracts at a different rate than the bulk, generating compressive stress that toughens the material. This thermally-driven process avoids complex mechanical reinforcement while achieving enhanced toughness

Inventive Principle:

Principle #37Thermal expansion

Solution Approach 2:

The patent replaces complex mechanical reinforcement structures with a thermally-induced stress field. Instead of adding physical layers or structural elements to increase toughness, the solution uses controlled thermal processing to create internal compressive stresses that provide the same protective function more simply

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

The ceramic component exhibits improved strength, reduced brittleness, and mitigated surface defect propagation, effectively protecting internal components from shock-related damage.

Implementation Method 1

diffusing at least a portion of the material into an external portion of the ceramic substrate

Methodology Applied

Scientific EffectDiffusion: Diffusion

Implementation Method 2

cooling the material and the ceramic substrate thereby generating a compressive stress within the external portion of the ceramic substrate

Methodology Applied

Scientific EffectThermal contraction: Thermal Contraction

Data Source

PatentUS11104616B2Ceramic having a residual compressive stress for use in electronic devices

Publication Date: 2021.08.31 APPLE INC

AI summary

A toughened ceramic component having a residual compressive stress and methods of forming the toughened ceramic component is disclosed. The ceramic component may include an internal portion having a first coefficient of thermal expansion (CTE) and an external portion substantially surrounding the internal portion and forming an exterior surface of the ceramic component. The external portion may have a second CTE that is less than the first CTE. Additionally, the external portion may be in compressive stress.