Micro-LED Driving Substrate Pad Thickness and Protection

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Solution Overview

Problem

Micro-LED display devices face challenges with first pad breakage and inadequate contact area during edge grinding due to their thin thickness, leading to instability and reduced yield in the manufacturing process.

Innovation Solution

The driving substrate features first pads with a thickness range of 0.5 to 2 microns, second pads with stacked sub-layers, a protective adhesive layer with specific hardness, and side traces formed via transfer printing, along with a chamfered vertex angle to enhance stability and contact area.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If the thickness of first pads is reduced to achieve finer pitch and higher resolution, then the resolution and pixel density are improved, but the pads become more prone to breakage and have insufficient contact area during edge grinding

Engineering Contradiction:

Improvepad thickness controlVSAvoidpad breakage resistance

Core Design Contradiction:

Manufacturing precisionVSReliability

Solution Approach 1:

The patent specifies a controlled thickness range of 0.5-2 microns for first pads, optimizing the parameter to balance resolution requirements with mechanical strength. This parameter optimization prevents pad breakage during edge grinding while maintaining the fine pitch needed for high resolution displays.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The first pads are constructed with composite material structure including a copper layer (third sub-layer) and a solder layer (fourth sub-layer). This composite structure provides both the electrical conductivity needed for signaling and the mechanical strength required to resist breakage during manufacturing processes like edge grinding.

Inventive Principle:

Principle #40Composite materials

2Reliability

If the thickness of first pads is increased to improve strength and contact area, then the reliability and manufacturing yield are improved, but the ability to achieve fine pitch and ultra-high resolution is compromised

Engineering Contradiction:

Improvepad contact areaVSAvoidpitch precision

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The patent establishes an optimized thickness range of 0.5-2 microns that simultaneously satisfies both fine pitch requirements for ultra-high resolution and sufficient contact area for reliable electrical connections. This parameter window allows the pads to be thin enough for high density while remaining thick enough to prevent breakage.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent introduces a multi-layer vertical structure (copper sub-layer plus solder sub-layer) to increase the effective contact area and strength in the vertical dimension, allowing the horizontal footprint to remain small for fine pitch while maintaining adequate mechanical and electrical properties through the stacked layers.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

3Area of stationary object

If edge grinding is performed to achieve narrow bezel and full-screen display, then the display area and aesthetic quality are improved, but the risk of pad breakage and manufacturing defects increases

Engineering Contradiction:

Improvedisplay areaVSAvoidpad breakage during processing

Core Design Contradiction:

Area of stationary objectVSObject-affected harmful factors

Solution Approach 1:

The patent employs beforehand cushioning by providing a protective adhesive layer covering the first pads before edge grinding occurs. This protective layer acts as a cushion that prevents direct mechanical stress on the thin pads during the edge grinding process, significantly reducing the risk of pad breakage while enabling narrow bezel fabrication.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

Solution Approach 2:

The first pads utilize composite material construction with copper and solder layers, where the solder layer (with higher ductility and toughness) serves as a protective outer layer that absorbs mechanical stress during edge grinding, cushioning the more brittle copper layer underneath and preventing pad fracture.

Inventive Principle:

Principle #40Composite materials

4Reliability

If protective adhesive layer with high hardness is used to protect pads during edge grinding, then the pad protection and manufacturing yield are improved, but the risk of pad damage due to stress and cracking increases

Engineering Contradiction:

Improvepad protection during processingVSAvoidadhesive layer stress on pads

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The patent specifies a controlled hardness range of 70-90 Shore D for the protective adhesive layer, optimizing this parameter to provide sufficient protection during edge grinding while maintaining flexibility to avoid generating excessive stress that could crack the thin first pads. This hardness window balances protective capability with stress mitigation.

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS11276674B2Driving substrate and manufacturing method thereof, and display device

Publication Date: 2022.03.15 BOE MLED TECH CO LTD

AI summary

A driving substrate includes a base substrate. The base substrate has a display region and a peripheral region, and the peripheral region includes a bonding region between the display region and a first side face of the base substrate. The driving substrate further includes a plurality of first pads spaced apart from each other, which are disposed in the bonding region of the base substrate. A first side face of each first pad is flush with the first side face of the base substrate. A thickness of the first pad is approximately in a range from 0.5 microns to 2 microns.