Rear-Mounted LED Light Pipe for Uniform PCB Legend Illumination

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Solution Overview

Problem

In touch-sensitive display panels with restricted space, existing backlighting solutions, such as LEDs, face challenges like limited space for mounting, uneven light distribution, and high costs due to the need for larger LEDs, which exacerbate issues with multiple LEDs and varying light intensity.

Innovation Solution

A diffusion-based illumination device with remotely located light sources, typically SMT LEDs mounted on the rear of a printed circuit board, uses a light pipe to direct and diffuse light through an aperture in the PCB to illuminate regions evenly, reducing the need for multiple LEDs and minimizing component count.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Illumination intensity

If standard LEDs are mounted on the PCB topside, then illumination is provided, but space is insufficient between PCB and fascia

Engineering Contradiction:

ImprovebacklightingVSAvoidmounting space

Core Design Contradiction:

Illumination intensityVSVolume of moving object

Solution Approach 1:

The patent inverts the conventional LED mounting approach by placing LEDs on the rear surface of the PCB rather than the topside. This allows the light to pass through the PCB and illuminate the fascia from behind, eliminating the space constraint between PCB and fascia while still providing the required illumination.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The patent transitions from a two-dimensional mounting problem (topside PCB surface) to a three-dimensional solution by utilizing the rear surface of the PCB. This dimensional change allows LED placement in a different spatial location that does not conflict with the fascia assembly.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Illumination intensity

If reverse through hole LED is used behind hole in PCB, then illumination is provided, but LED legs foul the fascia plastic

Engineering Contradiction:

ImprovebacklightingVSAvoidfascia contamination

Core Design Contradiction:

Illumination intensityVSObject-affected harmful factors

Solution Approach 1:

The patent extracts the problematic LED legs from the equation by using surface mount technology LEDs that are soldered to the PCB surface rather than through-hole LEDs that require legs passing through the PCB. This eliminates the source of fascia contamination while maintaining illumination functionality.

Inventive Principle:

Principle #2Taking out (Extraction)

3Area of stationary object

If larger LEDs are used to span the hole, then illumination coverage is improved, but cost increases due to size

Engineering Contradiction:

Improveillumination coverageVSAvoidLED size and cost

Core Design Contradiction:

Area of stationary objectVSQuantity of substance

Solution Approach 1:

The patent segments the illumination function by using multiple small SMT LEDs distributed across the PCB rear surface rather than relying on a single large LED. This segmentation allows each small LED to cover a portion of the required area, achieving full coverage through collective action of multiple components.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent combines the illumination output of multiple small LEDs to achieve the total light output and coverage area previously requiring a single large LED. This merging approach reduces individual component size and cost while maintaining overall illumination performance.

Inventive Principle:

Principle #5Merging (Combining)

4Volume of moving object

If LEDs are placed close to fascia, then space is saved, but light distribution becomes uneven with bright spots

Engineering Contradiction:

Improvemounting spaceVSAvoidlight distribution uniformity

Core Design Contradiction:

Volume of moving objectVSIllumination intensity

Solution Approach 1:

The patent introduces the PCB itself as an intermediary medium between the LEDs and the fascia. The light passes through the PCB material which acts as a diffusion medium, scattering the light rays and eliminating direct beam paths that cause bright spots. This intermediary approach achieves uniform illumination while maintaining compact spacing.

Inventive Principle:

Principle #24Intermediary (Mediator)

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 solution provides cost-effective, even backlighting for touch-sensitive display panels, reduces component failure rates, simplifies construction and maintenance, and allows for efficient use of space, while ensuring uniform illumination without bright spots.

Implementation Method 1

the light is diffused by the directing means as it moves along the path

Methodology Applied

Scientific EffectLight diffusion: Diffusion

Data Source

PatentUS7690828B2Illumination device

Publication Date: 2010.04.06 ARRIS ENTERPRISES LLC

AI summary

An illumination device comprising an LED (14) mounted on a rear of a PCB (12), and a light pipe (16) to direct light from the LED through an aperture (18) in the PCB to illuminate a legend (10) on the front of the PCB, the light pipe diffusing the light so as to prevent uneven illumination of the legend.