Semiconductor Light-Emitting Device Thermal Expansion Mismatch

Solution Overview

Problem

Conventional semiconductor light-emitting devices face reliability issues due to thermal expansion mismatch between encapsulating resins and wavelength converting materials during reflow soldering, leading to peeling and potential degradation of optical characteristics.

Innovation Solution

A semiconductor light-emitting device design featuring a base board with a through hole cavity and a thermal expansion coefficient mismatch between the encapsulating resin and wavelength converting material, where a space is created to prevent contact and stress between the two, using a silicone resin for the wavelength converting material and an epoxy resin for encapsulation, and a concave shape for the wavelength converting material's top surface to enhance light emission.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a wavelength converting material including silicone resin is used to cover the semiconductor light-emitting chip, then thermal resistance is improved and degradation of the wavelength converting material is prevented, but thermal expansion coefficient mismatch with the encapsulating resin causes peeling and cracks during reflow soldering

Engineering Contradiction:

Improveprevention of degradation of wavelength converting materialVSAvoidpeeling between encapsulating resin and wavelength converting material

Core Design Contradiction:

ReliabilityVSStability of the object's composition

Solution Approach 1:

A resin layer is formed between the encapsulating resin and the wavelength converting material to act as a stress-absorbing buffer. This intermediate resin layer prevents direct stress transmission during thermal expansion and contraction cycles, thereby preventing peeling and cracks while maintaining the thermal resistance benefits of the silicone-based wavelength converting material.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

Solution Approach 2:

An intermediate resin layer is introduced as a mediator between the encapsulating resin and the wavelength converting material. This intermediate layer has thermal expansion properties that bridge the gap between the two materials, reducing the mismatch stress and preventing interface failure during reflow soldering processes.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Stability of the object's composition

If an encapsulating resin with low thermal expansion coefficient is used, then dimensional stability is improved, but stress concentration occurs at the interface with the wavelength converting material during temperature changes

Engineering Contradiction:

Improvedimensional stability of encapsulating resinVSAvoidstress concentration at material interface

Core Design Contradiction:

Stability of the object's compositionVSStress or pressure

Solution Approach 1:

The resin layer is positioned beforehand between the encapsulating resin and wavelength converting material to cushion and distribute thermal stresses. This prevents stress concentration at the interface by providing a compliant intermediate zone that absorbs expansion and contraction forces during temperature cycling.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

3Device complexity

If the encapsulating resin directly contacts the wavelength converting material, then device structure is simplified, but cracks occur in the encapsulating resin during reflow soldering due to thermal expansion mismatch

Engineering Contradiction:

Improvestructure simplicity of encapsulating resin and wavelength converting material interfaceVSAvoidcrack prevention in encapsulating resin

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

A resin layer is formed between the encapsulating resin and the wavelength converting material to act as a stress-absorbing buffer. This intermediate resin layer prevents direct stress transmission during thermal expansion and contraction cycles, thereby preventing peeling and cracks while maintaining the thermal resistance benefits of the silicone-based wavelength converting material.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

Solution Approach 2:

An intermediate resin layer is introduced as a mediator between the encapsulating resin and the wavelength converting material. This intermediate layer has thermal expansion properties that bridge the gap between the two materials, reducing the mismatch stress and preventing interface failure during reflow soldering processes.

Inventive Principle:

Principle #24Intermediary (Mediator)

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 design enhances reliability by preventing cracks and maintaining high light-emitting efficiency and light-harvesting efficiency, even under high temperatures, with improved directional light distribution and reduced stress between materials.

Implementation Method 1

a part of the light emitted from a semiconductor light-emitting chip is converted into light having a different wavelength by a phosphor

Methodology Applied

Scientific EffectWavelength conversion by phosphor: Photoluminescence

Implementation Method 2

thermal expansion coefficient mismatch between the encapsulating resin and wavelength converting material

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Data Source

PatentUS8860047B2Semiconductor light-emitting device

Publication Date: 2014.10.14 STANLEY ELECTRIC CO LTD

AI summary

A reliable semiconductor light-emitting device can include a wavelength converting material in a cavity mounting at least one semiconductor light-emitting chip. The device can also include an encapsulating resin to cover the wavelength converting material so as to emit a wavelength-converted light using light emitted from the chip. The wavelength converting material should include a transparent resin having a large thermal expansion coefficient to maintain a high thermal resistance, and the encapsulating resin is subject to cracks due to a high transparent resin. The semiconductor device can be configured to form a space between the wavelength converting material and the encapsulating resin so that each of the encapsulating resin and the wavelength converting material cannot contact with each other even under a high temperature. Thus, the disclosed subject matter cannot stress in the encapsulating resin when the wavelength converting material expands, and therefore can provide the reliable semiconductor light-emitting device.