LED Phosphor Containment Structure for Wafer-Level Coating
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Solution Overview
Problem
Conventional methods for coating light emitting diodes (LEDs) with phosphor layers face challenges in controlling geometry and thickness, leading to non-uniform color temperature and inconsistent emission characteristics, and often require complex processes that make it difficult to access wire bond pads.
Innovation Solution
The method involves forming containment structures on LEDs at the wafer level to define deposition areas for phosphor and binder coatings, allowing for precise application while keeping wire bond pads accessible, enabling consistent and repeatable coating of LEDs with down-converter layers before dicing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional syringe or nozzle methods are used to inject phosphor mixed with epoxy resin or silicone polymers over the LED, then phosphor coating can be applied, but it is difficult to control the phosphor layer's geometry and thickness uniformly
Solution Approach 1:
The patent applies preliminary action by forming a cured layer of transparent binder material over the LED chip surface before applying the phosphor-containing binder. This pre-formed layer serves as a controlled substrate that enables precise geometric definition and thickness control of the subsequent phosphor coating, resolving the manufacturing precision issue while maintaining ease of manufacture
Solution Approach 2:
The patent introduces an intermediary cured binder layer between the LED chip and the phosphor-containing binder. This intermediary layer acts as a mediator that provides a controlled interface for phosphor deposition, enabling precise control over the phosphor layer's geometry and thickness while facilitating the coating application process
2Productivity
If stencil printing method is used to deposit phosphor composition in stencil openings, then multiple LEDs can be coated simultaneously, but the stenciling composition may not fully fill the stencil opening and can stick to the stencil opening reducing composition on the LED
Solution Approach 1:
The patent applies preliminary action by pre-forming a cured binder layer on the LED chip surface before phosphor deposition. This pre-formed layer creates a controlled receptacle that ensures complete filling during phosphor composition application, preventing both incomplete filling and stencil adhesion issues, thereby achieving uniform and consistent phosphor layers across multiple LEDs
Solution Approach 2:
The cured binder layer serves as an intermediary between the stencil and the LED chip. This intermediary layer prevents the phosphor-containing composition from sticking to the stencil opening while ensuring complete transfer and uniform distribution onto the LED surface, resolving both the filling and adhesion problems
3Ease of operation
If phosphor coating is applied at the package level after wire bonding, then wire bond access is maintained, but the process becomes costly and sensitive to packaging geometry effects
Solution Approach 1:
The patent applies preliminary action by performing the phosphor coating operation at the wafer level before dicing and packaging. The containment structures are formed and phosphor layers are deposited on the wafer substrate while multiple LED chips are still attached, maintaining wire bond pad accessibility throughout the process. This preliminary coating approach eliminates subsequent coating steps and reduces sensitivity to packaging geometry variations
Solution Approach 2:
The patent merges multiple operations by combining the phosphor coating process with the wafer-level fabrication and testing processes. By integrating phosphor deposition into the wafer fabrication sequence before dicing, the method combines several discrete steps into a unified process flow, reducing overall device complexity and eliminating the need for separate post-packaging coating operations
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 consistent fabrication and testing of LEDs at the wafer level with uniform phosphor coverage, eliminating the need for post-dicing phosphor application and simplifying the process, resulting in LEDs with stable emission characteristics and easier integration into packages.
Implementation Method 1
The surrounding phosphor material 'downconverts' the wavelength of some of the LED's blue light, changing its color to yellow
Data Source
AI summary
Methods for fabricating a semiconductor devices, and in particular light emitting diodes (LEDS) comprising providing a plurality of semiconductor devices on a substrate and forming a contact on at least some of the semiconductor devices. A containment structure is formed on at least some of the semiconductor devices having a contact with each containment structure defining a deposition area excluding the contact. A coating material is deposited then within the deposition area, with the coating material not covering the contact. A light emitting diode (LED) chip wafer comprising a plurality of LEDs on a substrate wafer with at least some of the LEDs having a contact. A plurality of containment structures are included, each of which is associated with a respective one of the plurality of LEDs. Each of the containment structures at least partially on its respective one of the LEDs and defining a deposition area on its respective one of the LEDs. The deposition area excludes the contact. A coating is included in each of the deposition areas.