Clustered Micro Pick-Up Arrays for High-Density Sequential Placement
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Solution Overview
Problem
Integration and packaging issues, particularly in transferring micro devices such as RF MEMS microswitches, LEDs, and quartz-based oscillators, are hindered by traditional direct printing and transfer printing methods that require de-bonding the transfer wafer and involve the entire wafer in the transfer process, limiting commercialization and efficiency.
Innovation Solution
A mass transfer tool with articulating transfer head assemblies and micro pick-up arrays, featuring clusters of transfer heads with intra- and inter-cluster spacing, enabling high-density pick and place operations using elastomeric contact, vacuum, or electrostatic principles, allowing for efficient transfer of micro devices between donor and receiving substrates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If traditional direct printing or transfer printing methods are used, then the transfer process can be performed with simpler equipment, but the throughput is low and device integrity is compromised due to de-bonding requirements
Solution Approach 1:
The transfer tool is segmented into multiple independent transfer heads arranged in arrays, with each head capable of handling individual micro devices. This segmentation enables parallel processing of multiple devices simultaneously, dramatically increasing throughput while maintaining simple individual head designs that avoid complex wafer-level operations
Solution Approach 2:
A release layer is introduced as an intermediary between the micro devices and the donor substrate, enabling non-destructive release of devices during transfer. This intermediary layer allows devices to be released without de-bonding the entire transfer wafer, preserving device integrity while enabling efficient transfer operations
2Productivity
If the entire transfer wafer is involved in the transfer process, then batch processing is achieved, but the process complexity increases due to de-bonding requirements and device integrity is compromised
Solution Approach 1:
The invention extracts the de-bonding step from the transfer process by using a release layer that allows direct release of individual devices or small groups from the donor substrate. This eliminates the need to de-bond an entire transfer wafer, maintaining batch processing capability while preserving device integrity through gentle, localized release mechanisms
Solution Approach 2:
The release layer serves as a mediator between the donor substrate and micro devices, enabling batch transfer operations without requiring de-bonding of the transfer wafer. This intermediary enables reliable device release while maintaining both batch processing efficiency and device integrity
3Productivity
If transfer heads are arranged with smaller spacing to increase density, then transfer capacity increases, but device protection decreases due to reduced shielding and compliance
Solution Approach 1:
Each transfer head is equipped with self-compliant mechanisms including flexible fingers and integrated force sensors that automatically adjust to device characteristics during contact. This self-service capability allows high-density arrangement while maintaining adequate protection, as each head independently adapts its contact force and positioning without requiring excessive spacing for external compliance mechanisms
Solution Approach 2:
Flexible contact surfaces and thin-film structures are used in the transfer head design, enabling close spacing between heads while maintaining compliance with devices. These flexible elements deform to accommodate device variations and provide cushioning protection, allowing high-density arrangements without compromising device integrity
4Manufacturing precision
If electrostatic transfer heads are used, then transfer precision improves through controlled electrostatic forces, but device sensitivity to stray electric fields increases
Solution Approach 1:
The transfer head design uses asymmetric electrode configurations where driven electrodes generate controlled electrostatic fields for precise positioning, while undiven electrodes and grounded shields create asymmetric field cancellation zones. This asymmetric arrangement maintains precise electrostatic control while directing stray fields away from devices, reducing their harmful effects
Solution Approach 2:
Grounded electrostatic shields and intermediate grounded layers are positioned between the electrostatic actuators and the micro devices. These intermediary grounded structures act as field barriers that block stray electric fields from reaching devices while allowing the controlled electrostatic forces needed for precise placement to act on the devices
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
The solution enables high-density transfer of micro devices with increased throughput and reduced costs, protecting device integrity through compliant transfer heads and electrostatic shielding, facilitating precise placement and higher pixel density on display substrates.
Implementation Method 1
the transfer heads operate in accordance with principles of electrostatic grippers, using the attraction of opposite charges to pick up the micro devices
Implementation Method 2
vacuum, or operate in accordance with electrostatic principles
Data Source
AI summary
Mass transfer tools and methods for high density transfer of arrays of micro devices are described. In an embodiment, a mass transfer tool includes a micro pick up array with an array of transfer heads arranged in clusters. The clusters of transfer heads can be used to pick up a high density group of micro devices followed by sequential placement onto a receiving substrate.