Composite Substrate LED Assembly Thermal Stress

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Solution Overview

Problem

Conventional semiconductor light-emitting element assemblies face challenges with heat dissipation due to thermal expansion coefficient differences between materials, leading to deformation and reduced reliability, and existing solutions are costly or inefficient.

Innovation Solution

A semiconductor light-emitting element assembly featuring a composite substrate with a thermal expansion coefficient ≤12×10−6/°C and thermal conductivity ≥150 W/mK, combined with a flexible adhesive layer and a recess structure for improved heat dissipation and reduced thermal stress, using materials like metal matrix composites, polymer matrix composites, or ceramic matrix composites.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Temperature

If a metal heat-dissipating plate (e.g., copper) is used, then heat dissipation performance is improved, but thermal expansion coefficient difference causes deformation and fatigue

Engineering Contradiction:

Improveheat dissipation performanceVSAvoiddeformation and fatigue

Core Design Contradiction:

TemperatureVSReliability

Solution Approach 1:

The patent uses a composite substrate comprising a metal substrate (providing heat dissipation) and a ceramic coating layer (providing low thermal expansion coefficient). This composite structure combines the advantages of both materials to achieve good heat dissipation while reducing thermal expansion coefficient difference with the LED chip.

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The ceramic coating layer is applied locally on the metal substrate surface where the LED chip is mounted. This localized approach provides low thermal expansion coefficient where needed (at the chip interface) while maintaining the overall heat dissipation capability of the metal substrate.

Inventive Principle:

Principle #3Local quality

2Reliability

If ceramic material (e.g., AlN) is used for heat-dissipating plate, then thermal expansion coefficient difference is reduced, but cost increases significantly

Engineering Contradiction:

Improvethermal expansion coefficient matchingVSAvoidmanufacturing cost

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

Instead of using expensive pure ceramic material throughout, the patent creates a composite structure with a cost-effective metal substrate and a relatively thin ceramic coating layer. This reduces the overall amount of expensive ceramic material needed while still achieving the desired thermal expansion coefficient matching at the critical interface.

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The patent uses a relatively thin ceramic coating layer rather than a thick ceramic substrate, reducing the quantity of expensive ceramic material required. This cost-effective approach maintains the essential function of thermal expansion coefficient matching without the full cost of a complete ceramic heat sink.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

3Device complexity

If mechanical connection method is used, then assembly is simple, but space requirement increases

Engineering Contradiction:

Improveassembly simplicityVSAvoidinstallation space

Core Design Contradiction:

Device complexityVSArea of stationary object

Solution Approach 1:

The patent integrates the LED chip directly onto the composite substrate using soldering, merging the mounting function with the heat dissipation function. This eliminates the need for separate mechanical mounting structures and reduces the overall assembly space required.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The patent replaces mechanical connection methods (screws, clips) with direct soldering connections. This substitution eliminates the need for mechanical fastening components and their associated space requirements, achieving a more compact assembly.

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 solution effectively reduces thermal stress and enhances heat dissipation performance while maintaining reliability and cost-effectiveness by minimizing thermal expansion coefficient differences and utilizing efficient heat transfer materials.

Implementation Method 1

a composite substrate with a thermal expansion coefficient substantially smaller than or equal to 12×10−6/° C., and with a thermal conductivity coefficient substantially greater than or equal to 150 W/mK

Methodology Applied

Scientific EffectThermal conduction: Conduction (thermal)

Implementation Method 2

The difference between the thermal expansion coefficients is likely to cause deformation and fatigue between the LED (12) and the heat-dissipating plate (10) under high temperature

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Data Source

PatentUS7745832B2Semiconductor light-emitting element assembly with a composite substrate

Publication Date: 2010.06.29 ENNOSTAR CORP

AI summary

A semiconductor light-emitting element assembly, comprising a composite substrate, a circuit layout carrier, a connecting structure, a recess, and a semiconductor light-emitting element, is disclosed. The connecting structure is used for bonding the composite substrate with the circuit layout carrier. The recess is formed by the circuit layout carrier and extends toward the composite substrate. The semiconductor light-emitting element is deposited in the recess and electrically connected to the circuit layout carrier.