Two-Stage Singulation for Phosphor-Coated LED Wafers
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Solution Overview
Problem
The mechanical dicing of phosphor-coated wafers for light emitting devices results in a wider kerf width, requiring increased spacing between elements and reducing wafer area utilization, as laser dicing damages the phosphor layer.
Innovation Solution
A two-stage singulation process is employed, where light emitting elements are initially laser-diced before phosphor application, and then mechanically diced after phosphor coating, using a flexible film to accommodate the wider kerf width by stretching the film to provide necessary spacing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If mechanical dicing is used for phosphor-coated wafers, then the phosphor layer is not damaged, but the kerf width increases from 10-15 um to 50-100 um
Solution Approach 1:
The patent divides the singulation process into two separate stages: first laser dicing before phosphor coating to create initial separations, then mechanical dicing after coating to complete the separation. This segmentation allows each process to be optimized independently - laser for precision and mechanical for phosphor protection.
Solution Approach 2:
The patent performs preliminary laser dicing before phosphor coating to create initial gaps between elements. This preliminary action reduces the burden on the subsequent mechanical dicing step, allowing smaller streets while still accommodating the wider mechanical kerf width.
2Reliability
If wider kerf width is used for mechanical dicing, then phosphor layer is protected, but wafer area utilization decreases from 90% to 36%
Solution Approach 1:
By segmenting the dicing process into two stages, the patent achieves both wide mechanical kerfs for phosphor protection and high wafer utilization. The first laser stage creates precise initial separations, enabling tighter element spacing that compensates for the wider mechanical kerf width.
Solution Approach 2:
The patent changes the state of the wafer between dicing operations - first dicing in the uncoated state with laser, then after phosphor coating with mechanical means. This parameter change (coating state) enables optimization of both kerf width and street width independently.
3Manufacturing precision
If laser dicing is used after phosphor coating, then precise cuts are achieved, but the phosphor layer is damaged
Solution Approach 1:
The patent performs the laser dicing action before phosphor coating, when the phosphor layer is not yet present to be damaged. This preliminary action achieves precise cuts without exposing phosphor to harmful laser energy.
Solution Approach 2:
The patent extracts the harmful interaction between laser and phosphor by performing laser dicing at a different stage - before phosphor coating. This separates the precision-cutting function from the phosphor-protection requirement.
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 significantly increases wafer area utilization, from 36% to 88% for 500x500 um dies and from 64% to 94% for 1000x1000 um dies, while maintaining the ability to apply phosphor in a wafer-scale process.
Implementation Method 1
the tape is stretched to provide space between the individual light emitting elements that allows for the wider kerf width of the subsequent mechanical dicing
Data Source
AI summary
A two-stage singulation process is used in the fabrication of phosphor coated light emitting elements. Prior to the application of the phosphor coating, the individual light emitting elements are singulated using a laser dicing process; after application of the phosphor coating, the phosphor coated light emitting elements are singulated using a mechanical dicing process. Before laser dicing of the light emitting elements, the wafer is positioned on a piece of dicing- or die-attach-tape held by a frame; after laser dicing, the tape is stretched to provide space between the individual light emitting elements that allows for the wider kerf width of the subsequent mechanical dicing after application of the phosphor coating.