Optical Module Resin Filling for Thermal-Stable Bump Joints

Solution Overview

Problem

The use of underfill materials with large thermal expansion in optical modules leads to breakage of bump joints due to thermal stress, especially when electrodes are disposed on one side of the optical element, causing deformation and stress concentration at the joints.

Innovation Solution

A method involving the use of optical transparent resin with low thermal expansion, photocured between the substrate and optical element, and encapsulation resin with even lower thermal expansion to seal the module, ensuring the bump joints are not subjected to large stress.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Illumination intensity

If an optical transparent resin without filler is used to fill the gap between substrate and optical element, then light transmission is improved, but thermal expansion increases causing bump joint breakage

Engineering Contradiction:

Improvelight transmissionVSAvoidbump joint integrity

Core Design Contradiction:

Illumination intensityVSReliability

Solution Approach 1:

The underfill material is divided into two distinct segments: an optical transparent resin segment without filler for light transmission, and a separate encapsulation resin segment with filler for thermal stability. This segmentation allows each material to perform its specialized function without compromise.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the gap are filled with different materials having different properties. The region requiring optical clarity receives filler-free transparent resin, while the region requiring thermal stability receives filler-containing encapsulation resin. This local differentiation resolves the contradiction by assigning appropriate material properties to specific locations.

Inventive Principle:

Principle #3Local quality

2Reliability

If a filler such as silica is contained in the optical transparent resin, then thermal expansion is reduced, but light is scattered or blocked

Engineering Contradiction:

Improvethermal stabilityVSAvoidlight transmission

Core Design Contradiction:

ReliabilityVSIllumination intensity

Solution Approach 1:

The underfill material is divided into two distinct segments: an optical transparent resin segment without filler for light transmission, and a separate encapsulation resin segment with filler for thermal stability. This segmentation allows each material to perform its specialized function without compromise.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the gap are filled with different materials having different properties. The region requiring optical clarity receives filler-free transparent resin, while the region requiring thermal stability receives filler-containing encapsulation resin. This local differentiation resolves the contradiction by assigning appropriate material properties to specific locations.

Inventive Principle:

Principle #3Local quality

3Device complexity

If electrodes are disposed only on one side of the optical element, then device complexity is reduced, but thermal stress causes greater deformation and bump joint breakage

Engineering Contradiction:

Improveelectrode configurationVSAvoidbump joint integrity

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The encapsulation resin with low thermal expansion coefficient is specifically applied to the electrode-side region of the optical element, providing localized thermal compensation exactly where the bump joints are located. This targeted approach compensates for the asymmetry caused by single-sided electrode configuration.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The encapsulation resin is applied in advance to cushion and compensate for thermal expansion effects before thermal stress is applied. This pre-positioned protective layer prevents deformation and protects bump joints from thermal stress, especially on the non-electrode side where deformation would be greatest.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

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 method effectively suppresses breakage of bump joints by minimizing thermal deformation, ensuring the optical module's structural integrity under thermal stress.

Implementation Method 1

a step of applying light through the optical waveguide toward the at least one of the light reception unit and the light emission unit to photocure the optical transparent resin located between the optical waveguide and the at least one of the light reception unit and the light emission unit

Methodology Applied

Scientific EffectPhotocuring: Photopolymerisation

Data Source

PatentUS20250389907A1Method for producing optical module, and optical module

Publication Date: 2025.12.25 PANASONIC INTELLECTUAL PROPERTY MANAGEMENT CO LTD

AI summary

A method for producing an optical module includes: a step of bonding an electrode formed on a surface of a substrate and an electrode described on a surface of an optical element via a bump; a step of injecting an optical transparent resin to be cured by light into a gap between the substrate and the optical element; a step of applying light through an optical waveguide, formed on the substrate, toward a light reception unit formed on the optical element to photocure the optical transparent resin located between the optical waveguide and the light reception unit; a step of removing an uncured portion of the optical transparent resin; a step of injecting a encapsulation resin that has a coefficient of thermal expansion smaller than that of the optical transparent resin and is to be cured by heat into the gap between the substrate and the optical element; and a step of thermally curing the encapsulation resin.