Alkaline Cleaning for Selective Gallium Removal on LED Chips
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Solution Overview
Problem
The challenge in producing LED mounting substrates is the unintentional precipitation of metal Ga during laser lift-off, leading to connection failures due to dissolution or alteration of bumps on LED chips by acidic cleaning solutions.
Innovation Solution
A method using an alkaline cleaning solution with specific concentration, temperature, and time conditions to selectively remove Ga without affecting other metals on the LED chips, such as bumps, by immersing the LED chips in an alkaline solution with pH ranging from 9.5 to 14.0, containing sodium hydroxide or potassium hydroxide, and other alkalis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an acidic cleaning solution is used to remove metal Ga from LED chips, then metal Ga is removed, but the bump metals are dissolved or altered causing connection failure
Solution Approach 1:
The patent changes the chemical parameter of the cleaning solution from acidic to alkaline. This parameter change enables selective removal of metal Ga while preserving bump metals, as alkaline solutions do not dissolve metals like In, Sn, Ag, or Cu that constitute the bumps, thereby preventing connection failures
Solution Approach 2:
The patent converts the harmful effect of metal Ga precipitation into a beneficial selective cleaning process. By using alkaline cleaning solution, the metal Ga that precipitates during LLO becomes a removable contaminant that can be selectively eliminated without harming other components, turning a process defect into a controllable cleaning opportunity
2Object-affected harmful factors
If the bump is deeply embedded into the adhesive layer to protect it from the cleaning solution, then the bump is protected, but separation of the adhesive layer from the bump becomes difficult
Solution Approach 1:
Instead of protecting the bump by embedding it deeper into the adhesive layer, the patent inverts the approach by making the cleaning solution itself selective - using alkaline solution that naturally protects the bump through chemical selectivity rather than physical embedding, thus avoiding the separation difficulty while maintaining protection
3Reliability
If a cleaning method is developed to selectively remove Ga without affecting other metals, then connection failure is reduced, but the cleaning process becomes more complex
Solution Approach 1:
The patent achieves selective cleaning by changing a single fundamental parameter - the pH of the cleaning solution from acidic to alkaline. This simple parameter change provides inherent selectivity based on differential chemical reactivity, avoiding the need for complex multi-step processes or specialized equipment while maintaining high connection 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
This method produces high-quality LED mounting substrates with reduced connection failures by ensuring selective removal of Ga without altering the bump metals, thereby improving production yield and reducing costs.
Implementation Method 1
metals used for the bump (such as In or SnAgCu-based alloy (SAC)) and Ga (gallium) are often proximate in a periodic table, and it is considered that selective removal of gallium is difficult in a state where the bump and gallium are in contact with the cleaning solution
Implementation Method 2
laser lift-off (LLO) is performed to separate micro-LED chips from the sapphire substrate. The LLO step, for example, is a step of irradiating a GaN layer of the LED chip with an excimer laser to decompose the GaN layer into gaseous N2 and metal Ga
Implementation Method 3
irradiating a GaN layer of the LED chip with an excimer laser to decompose the GaN layer into gaseous N2 and metal Ga
Data Source
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AI summary
The present invention is a method for producing an LED mounting substrate, the method includes a step of cleaning an LED chip, being transferred from on top of a sapphire substrate onto a receptor substrate by laser lift-off, with an alkaline cleaning solution. This provides: the method for producing an LED mounting substrate capable of producing the LED mounting substrate by selectively removing metal Ga adhered to the LED chip, which has been transferred from the top of the sapphire substrate onto the receptor substrate by laser lift-off, without dissolving or altering another metal; a cleaning solution usable for this method; a cleaning method for selectively removing the gallium adhered to the LED chip without dissolving or altering the other metal; and a cleaning method for selectively removing gallium from a component having the gallium and a metal other than the gallium on a surface without dissolving or altering the metal other than the gallium.