Optical Module Thermal Stress Mitigation via Flexible PCB

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Solution Overview

Problem

Conventional optical modules experience fluctuations in characteristics due to temperature changes, causing stress and positional displacement between the planar lightwave circuit (PLC) and photodiode (PD) packages, resulting from differing thermal expansion coefficients between the PLC, printed circuit board, and housing.

Innovation Solution

The optical module incorporates a housing with a protrusion to fix the PLC, using elastic adhesive and flexible printed circuits to connect packages, and a printed circuit board with spaces or notches to absorb thermal stress, allowing for movement and reducing stress on PD packages.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Stability of the object's composition

If the PLC, printed circuit board, and housing are rigidly fixed together, then structural stability is improved, but thermal stress causes positional displacement and characteristic fluctuation due to different thermal expansion coefficients

Engineering Contradiction:

Improvestructural stabilityVSAvoidcharacteristic stability under temperature fluctuation

Core Design Contradiction:

Stability of the object's compositionVSReliability

Solution Approach 1:

The patent introduces a flexible printed circuit board that can bend and deform to accommodate thermal expansion differences between the PLC substrate and housing. This flexible connection allows the system to maintain structural integrity while absorbing thermal stress, preventing positional displacement of optical components during temperature fluctuations.

Inventive Principle:

Principle #30Flexible shells and thin films

Solution Approach 2:

The patent changes the mechanical parameters of the connection structure by using a flexible printed circuit board with specific bending radius and elasticity characteristics. This allows the connection to dynamically adjust its stiffness parameter in response to thermal stress, maintaining optimal optical coupling while accommodating expansion differences.

Inventive Principle:

Principle #35Parameter changes

2Device complexity

If the PD packages are used to fix both the PLC and provide electrical connection, then device complexity is reduced, but thermal stress concentrates on the PD packages causing positional displacement

Engineering Contradiction:

Improvefixing structure complexityVSAvoidthermal stress on PD packages

Core Design Contradiction:

Device complexityVSStress or pressure

Solution Approach 1:

The patent separates the optical fixing function and electrical connection function into independent components. The PLC is fixed to the housing using a dedicated mechanical structure, while the PD packages are electrically connected through the flexible printed circuit board. This segmentation distributes thermal stress away from the PD packages, preventing positional displacement while maintaining functional integration.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The flexible printed circuit board acts as an intermediary element that provides electrical connection without bearing the mechanical load of fixing the PLC. This mediator absorbs thermal expansion differences and protects the PD packages from concentrated thermal stress, maintaining both electrical functionality and optical alignment.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Manufacturing precision

If rigid connections are used between components, then manufacturing precision is improved, but thermal expansion causes stress and characteristic fluctuation

Engineering Contradiction:

Improveassembly precisionVSAvoidoperational stability under temperature change

Core Design Contradiction:

Manufacturing precisionVSReliability

Solution Approach 1:

The patent transitions from rigid static connections to a dynamic flexible connection system. The flexible printed circuit board can dynamically adjust its shape and position in response to thermal stress, maintaining optimal electrical connection and optical alignment across varying temperature conditions while preserving manufacturing precision during assembly.

Inventive Principle:

Principle #15Dynamics

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 configuration effectively mitigates thermal fluctuations in characteristics by reducing stress and positional displacement between the PLC and PD packages, enhancing the stability of the optical module.

Implementation Method 1

fixing the PLC to a protrusion of a bottom section of the housing by means of elastic adhesive

Methodology Applied

Scientific EffectElasticity: Elasticity

Implementation Method 2

the PLC, printed circuit board, and the housing have different thermal expansion coefficients. Thus, when the optical module has a temperature fluctuation, each size of the substrate, the printed circuit board and the housing varies respectively

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Data Source

PatentUS8545111B2Optical module

Publication Date: 2013.10.01 NIPPON TELEGRAPH & TELEPHONE CORP

AI summary

An optical module has a structure for reducing the stress applied to a package. The optical module is structured so that an end face of a waveguide (37) of a planar lightwave circuit (30) is joined to a plurality of packages (40) storing therein optical elements so that the waveguide is optically coupled to the optical elements. The optical module includes a housing (3) storing therein a planar lightwave circuit and a plurality of packages in which an upper face of a protrusion (270) formed in the bottom section is fixed to the planar lightwave circuit (30). Each of the plurality of packages (40) is electrically connected to an electric part (22) provided in the housing (3) via flexible printed circuits (271a, 271b).