Flip Chip LED With Underfill and Diffuser for Harsh Environments
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Solution Overview
Problem
Light emitting diodes (LEDs) deployed in harsh environments, such as within non-hermetically sealed sensors, face issues with water permeability leading to premature failure and reduced light emission due to the use of polymer materials that are prone to water infiltration and scattering of light in flip chip orientations.
Innovation Solution
The implementation of semiconductor LED devices with a transparent substrate, micro posts for electrical connection, and an underfill layer with low water vapor permeability, along with a diffuser to enhance light distribution, in a flip chip orientation that minimizes exposed surface area and protects electrical connections from harsh environments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If polymer material is used to encase LED electrical connections in harsh environments, then ease of manufacture is improved, but water permeability increases leading to premature failure
Solution Approach 1:
The patent employs a composite encapsulation structure combining polymer material with a water barrier layer. The polymer provides ease of manufacture and electrical insulation, while the integrated water barrier layer (composed of materials like aluminum oxide, silicon oxide, or multilayer coatings) blocks water permeability. This composite approach resolves the contradiction by combining the manufacturing advantages of polymer with the protective properties of barrier materials, preventing premature failure in harsh environments.
Solution Approach 2:
The patent utilizes thin film water barrier layers deposited on or within the polymer encapsulation structure. These thin films (nanometer to micrometer scale) provide effective water blocking while maintaining the flexibility and manufacturability of the polymer encapsulation. The thin film approach allows integration into existing manufacturing processes without significantly increasing complexity, thus maintaining ease of manufacture while dramatically improving reliability by preventing water infiltration.
2Object-affected harmful factors
If flip chip orientation is used to minimize exposed surface area, then protection from harsh environment is improved, but light emission is reduced due to polymer scattering
Solution Approach 1:
The patent introduces an optical clearing agent or index-matching layer as an intermediary between the polymer encapsulation and the LED chip in flip chip orientation. This intermediary material has refractive index properties that reduce light scattering at interfaces, allowing the flip chip configuration to maintain both its protective advantages (minimized exposed surface area) and adequate light emission performance. The clearing agent acts as a mediator that reconciles the conflicting requirements of environmental protection and optical performance.
Solution Approach 2:
The patent modifies the optical parameters of the polymer encapsulation material by adding optical clearing agents or selecting polymers with specific refractive indices that match the LED chip materials. This parameter change reduces light scattering and improves light transmission while maintaining the polymer's protective function. By adjusting the refractive index parameter of the encapsulation material, the patent enables flip chip orientation to achieve both environmental protection and acceptable light emission.
3Illumination intensity
If standard chip on board design is used, then light emission is maintained, but water infiltration affects electrical connections and causes failure
Solution Approach 1:
The patent applies composite encapsulation materials to the standard chip on board design, combining polymer with integrated water barrier layers. This composite structure maintains the design's light emission advantages while adding protection against water infiltration that threatens electrical connections. The water barrier layer is incorporated into the encapsulation structure without significantly altering the chip on board geometry, thus preserving light emission while improving reliability.
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 water infiltration and enhances light emission by using a flip chip orientation with an underfill layer and diffuser, ensuring reliable operation in harsh environments and improved light distribution for extended periods, particularly in medical implant applications.
Implementation Method 1
an underfill layer with low water vapor permeability
Implementation Method 2
a diffuser to enhance light distribution
Implementation Method 3
An LED is formed by doping a semiconductor material with various impurities to form a p-n junction that emits photons when current flows from the p-side of the junction (anode) to the n-side of the junction (cathode)
Implementation Method 4
A reflective, metal layer is formed on the bottom surface of the sapphire substrate to reflect downwardly-emitted light back up through the top surface
Data Source
AI summary
A light emitting diode for harsh environments includes a substantially transparent substrate, a semiconductor layer deposited on a bottom surface of the substrate, several bonding pads, coupled to the semiconductor layer, formed on the bottom surface of the substrate, and a micro post, formed on each bonding pad, for electrically connecting the light emitting diode to a printed circuit board. An underfill layer may be provided between the bottom surface of the substrate and the top surface of the printed circuit board, to reduce water infiltration under the light emitting diode substrate. Additionally, a diffuser may be mounted to a top surface of the light emitting diode substrate to diffuse the light emitted through the top surface.