LED Chip Laser Bonding for Clean, Precise Display Mounting

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Solution Overview

Problem

The existing methods for mounting LED chips on circuit boards face challenges such as contamination of semiconductor elements by adhesive layers, complex processing techniques for forming electrode protrusions, and misregistration of LED chips during the joining process.

Innovation Solution

A manufacturing method involving the formation of a connecting electrode on a circuit board, an adhesive layer on the electrode, and laser-irradiation to melt-join the connecting electrode with the LED chip's terminal electrode, forming a eutectic alloy with a higher carbon concentration, which temporarily fixes the LED chip and prevents misregistration.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If an adhesive layer is used to join LED chips and circuit boards, then the LED chips can be mounted on the circuit board, but semiconductor elements may be contaminated by alkaline components in the adhesive layer

Engineering Contradiction:

Improvemounting processVSAvoidcontamination

Core Design Contradiction:

Ease of manufactureVSObject-affected harmful factors

Solution Approach 1:

The patent extracts and removes the adhesive layer from the joining process, replacing it with a direct solder bump connection between the LED chip electrode pad and the circuit board electrode pad. This eliminates the source of alkaline contamination while maintaining the mounting function.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent introduces solder bumps as an intermediary element between the LED chip and circuit board, replacing the adhesive layer. The solder bumps provide both mechanical connection and electrical connection, eliminating the need for adhesive and thus preventing contamination.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If electrode protrusions are formed on LED chip electrode pads to penetrate the adhesive layer, then electrical connection can be achieved, but complex processing techniques are required

Engineering Contradiction:

Improveelectrical connectionVSAvoidprocessing technique

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

Instead of forming protrusions on the LED chip side to penetrate the adhesive, the patent inverts the approach by forming solder bumps on the circuit board side that rise to contact the LED chip electrode pad. This simplifies the processing by eliminating the need for complex protrusion formation on the chip.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The patent replaces the mechanical protrusion formation process with a soldering process. Solder bumps are formed on the circuit board electrode pad and automatically rise to contact the LED chip electrode pad during reflow soldering, achieving both mechanical and electrical connection without complex mechanical processing.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Ease of manufacture

If adhesive layers are used for joining, then LED chips can be attached to the circuit board, but misregistration of LED chips during the joining process occurs

Engineering Contradiction:

Improveattachment processVSAvoidalignment

Core Design Contradiction:

Ease of manufactureVSManufacturing precision

Solution Approach 1:

The patent replaces the adhesive-based mechanical attachment system with a solder bump-based system. The solder bumps provide precise positional registration through their fixed geometry and strong bonding, eliminating the misregistration issues associated with adhesive layers that can shift or spread during curing.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent changes the bonding mechanism from adhesive bonding (which involves viscosity, curing time, and potential shifting) to solder bonding (which involves melting point, surface tension, and fixed geometric constraints). This parameter change ensures precise alignment and prevents misregistration during the joining process.

Inventive Principle:

Principle #35Parameter changes

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 simplifies the LED chip mounting process, reduces contamination risks, and ensures precise alignment and firm attachment of LED chips, enhancing the reliability and transparency of the display device.

Implementation Method 1

joining the connecting electrode and the terminal electrode by irradiating a laser light

Methodology Applied

Scientific EffectLaser heating: Laser

Implementation Method 2

irradiating a laser light... joining the connecting electrode and the terminal electrode

Methodology Applied

Scientific EffectMelting: Melting

Implementation Method 3

An alloy layer that joins the connecting electrode to the terminal electrode... has a higher concentration of carbon than the connecting electrode and the terminal electrode

Methodology Applied

Scientific EffectDiffusion: Diffusion

Data Source

PatentUS11894335B2Display device and method for manufacturing the same

Publication Date: 2024.02.06 JAPAN DISPLAY INC

AI summary

A method for manufacturing a display device includes preparing a circuit board including a drive circuit for driving a LED chip, forming a connecting electrode on the circuit board, forming an adhesive layer on the connecting electrode, adhering a terminal electrode of the LED chip on the adhesive layer and joining the connecting electrode and the terminal electrode by irradiating a laser light. The adhesive layer may be formed only on a upper surface of the connecting electrode.