Liquid-Assisted Micro Cold Binding for Indium Electrodes
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Solution Overview
Problem
The transfer process of micro devices to a substrate is challenging, particularly in bonding them securely to a conductive pad, as existing methods struggle with achieving strong and reliable electrical contact.
Innovation Solution
A method of liquid-assisted micro cold binding is employed, where a conductive indium pad is formed on a substrate, a liquid layer is created, and a micro device with an indium electrode is placed over it, gripped by capillary force, and then the liquid is evaporated to establish a strong electrical connection between the electrode and the pad.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional bonding methods are used for micro devices, then the bonding process is simple, but the bonding strength and electrical contact reliability are insufficient for small-dimensional micro devices
Solution Approach 1:
A liquid layer is introduced as an intermediary substance between the micro device electrode and the conductive pad. This liquid layer generates capillary force during evaporation to enhance bonding strength, while also facilitating electrical contact. The liquid mediator resolves the contradiction by providing a mechanism that simultaneously improves bonding reliability and electrical contact without requiring complex high-temperature or high-pressure equipment.
Solution Approach 2:
The method changes the physical state parameters of the bonding interface by introducing a liquid phase that transitions to vapor phase. The liquid layer's capillary pressure (a physical parameter) is utilized during evaporation to maintain strong bonding force. This parameter change approach enables reliable bonding of small-dimensional devices without complicating the overall process infrastructure.
2Manufacturing precision
If micro devices with small dimensions are bonded, then the precision is high, but the capillary force from liquid layer becomes insufficient to grip the device
Solution Approach 1:
The bonding system uses a composite approach combining liquid layer (providing capillary force) with indium material (providing strong metallic bonding and electrical conductivity). The indium conductive pad and indium electrode combination enhances the overall bonding strength beyond what liquid capillary force alone could provide for small-dimensional devices, while maintaining placement precision.
Solution Approach 2:
The method utilizes the curvature and surface tension characteristics of the liquid layer to maximize capillary force generation. The liquid's surface curvature during evaporation creates enhanced capillary pressure that effectively grips even small-dimensional micro devices, resolving the force insufficiency issue while maintaining precision placement.
3Strength
If liquid layer is used to grip micro device, then the bonding strength increases, but the process time increases due to evaporation step
Solution Approach 1:
The liquid layer is used as a temporary, disposable medium that serves its purpose during bonding and then evaporates completely. This short-living liquid phase provides strong gripping force during the critical bonding moment, then disappears without requiring removal steps, thus minimizing additional process time while maximizing bonding strength during the operation.
Solution Approach 2:
The evaporation step is designed to occur rapidly by skipping intermediate drying stages. The liquid layer transitions quickly from liquid to vapor phase, providing the necessary capillary force for bonding in a condensed time window. This rushing through the phase transition minimizes the time penalty while maintaining bonding strength.
4Reliability
If indium material is used for conductive pad and electrode, then the electrical conductivity is excellent, but the material cost increases
Solution Approach 1:
Indium material is applied locally only at the critical bonding interface where electrical contact is required (conductive pad and electrode contact areas), rather than throughout the entire device structure. This localized application maintains excellent electrical conductivity at the bonding interface while minimizing the total quantity of expensive indium material used, resolving the contradiction between reliability and material quantity.
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 enhances the solidity and reliability of the binding process, ensuring the micro device remains securely attached and facilitates subsequent processes, particularly effective for micro devices with small dimensions where traditional methods fail due to capillary force limitations.
Implementation Method 1
the micro device is in contact with the liquid layer and is gripped by a capillary force produced by the liquid layer between the micro device and the conductive pad
Implementation Method 2
evaporating the liquid layer such that the electrode is bound to the conductive pad and is in electrical contact with the conductive pad
Data Source
AI summary
A method of liquid assisted micro cold binding is provided. The method includes: forming a conductive pad on the substrate in which the conductive pad consists essentially of indium; forming a liquid layer on the conductive pad; placing a micro device having an electrode facing the conductive pad over the conductive pad such that the micro device is in contact with the liquid layer and is gripped by a capillary force produced by the liquid layer between the micro device and the conductive pad in which the electrode consists essentially of indium; and evaporating the liquid layer such that the electrode is bound to the conductive pad and is in electrical contact with the conductive pad.