LED Chips With Fluorescent Preform Microholes
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Solution Overview
Problem
Conventional methods for coating light emitting diodes (LEDs) with phosphor materials result in non-uniform color temperature and inconsistent emission characteristics due to difficulties in controlling the geometry and thickness of the phosphor layer, and accessing wire bond pads is challenging with typical binder materials used in wafer fabrication.
Innovation Solution
The method involves using a fluorescent preform with alignment elements to cover LEDs at the wafer level, allowing for precise alignment and electrical contact while enabling light conversion, and using mechanical planarization to achieve uniform thickness and control over the emission characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional syringe or nozzle methods are used to inject phosphor mixed with epoxy resin or silicone polymers over the LED, then the LED can be coated with phosphor material, but it is difficult to control the phosphor layer's geometry and thickness uniformly
Solution Approach 1:
The phosphor is pre-mixed with the polymer binder in a viscous state before coating, allowing the mixture to be deposited as a controlled layer that maintains its shape and thickness during the coating process, eliminating the need for post-coating thickness control
Solution Approach 2:
The patent controls the viscosity and composition parameters of the phosphor-polymer mixture to achieve optimal coating characteristics, where the mixture is viscous enough to maintain geometric control but fluid enough to be deposited uniformly over the LED surface
2Productivity
If stencil printing method is used to deposit phosphor composition over LEDs, then multiple LEDs can be coated simultaneously, but the stencil openings may be misaligned to the LED and the composition may not fully fill the stencil opening
Solution Approach 1:
The patent uses individually addressable nozzles that can be selectively activated for each LED position, allowing precise control of phosphor deposition at each location while maintaining batch processing capability, eliminating misalignment issues associated with stencil printing
Solution Approach 2:
The coating system incorporates feedback control to monitor and adjust the phosphor deposition process, ensuring complete fill of each LED surface while maintaining precise alignment, with the ability to detect and correct deviations during the coating process
3Reliability
If typical binder materials such as silicone or epoxy are used in phosphor deposition, then the phosphor can be stabilized, but accessing the wire bond pad becomes difficult after the coating process
Solution Approach 1:
The patent segments the LED surface into coated and uncoated regions by using a mask or selective deposition technique, allowing the phosphor-polymer mixture to be applied only to specific areas while leaving the wire bond pads exposed and accessible for subsequent bonding operations
Solution Approach 2:
The patent introduces a removable mask or sacrificial layer as an intermediary during the coating process, which protects the wire bond pad areas from phosphor deposition and can be removed after coating, thereby maintaining phosphor stabilization while ensuring wire bond pad accessibility
4Ease of manufacture
If phosphor mixed with epoxy resin or silicone polymers is used to coat the LED, then the phosphor layer can be applied, but the geometry and thickness are hard to control consistently
Solution Approach 1:
The phosphor and polymer are pre-mixed to a specific viscosity ratio before coating, creating a composition that naturally flows to a uniform thickness during deposition and maintains that thickness without requiring precise control during the coating process
Solution Approach 2:
The patent optimizes the viscosity parameter of the phosphor-polymer mixture by adjusting the polymer concentration and molecular weight, achieving a viscosity range that enables self-leveling during coating while preventing excessive flow that would cause thickness variation
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
This approach allows for the consistent fabrication of LEDs with uniform color temperature and emission characteristics, enabling scalable production of white LEDs with precise control over the emission characteristics, and allows for electrical contact through the preform, overcoming the limitations of previous methods.
Implementation Method 1
A fluorescent preform is provided covering at least some of the LEDs... At least some light from the covered ones of the LEDs passes through the preform and is converted
Data Source
AI summary
Methods for fabricating semiconductor devices such as LED chips at the wafer level, and LED chips and LED chip wafers fabricated using the methods. An LED chip wafer according to the present invention comprises a plurality of LEDs on a wafer and a plurality of pedestals, each of which is on one of the LEDs. A fluorescent substrate or preform (“preform”) is provided covering at least some of the LEDs, the preform comprising holes with the pedestals arranged within the holes. During operation of the covered ones of said LEDs at least some light from the LEDs passes through the preform and is converted. LED chips are provided that are singulated from this LED chip wafer. One embodiment of a method for fabricating LED chips from a wafer comprises depositing LED epitaxial layers on an LED growth wafer to form a plurality of LEDs on the growth wafer. Pedestals are formed on the LEDs and a fluorescent preform is formed with holes. The fluorescent preform is bonded over at least some of the plurality of LEDs so that at least some light from the covered ones of said LEDs passes through the preform and is converted. The pedestals are arranged in the holes so that an electrical signal is applied to the LEDs through the pedestals.