Adhesive Bonding Composition for Hidden-Joint Ambient Curing

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Solution Overview

Problem

Conventional photoinitiators for polymer curing require direct line-of-sight access to a light source, limiting their use in applications like multilayer silicon die stacks and causing thermal expansion mismatches during curing, which can lead to stress and warpage issues.

Innovation Solution

A curable adhesive composition comprising a polymerizable monomer, a photoinitiator responsive to specific wavelengths of light, and an energy converting material that emits this wavelength when exposed to ionizing radiation, allowing for indirect photoinitiation and ambient temperature curing without thermal expansion mismatches.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of operation

If conventional photoinitiators are used for polymer curing, then curing can be achieved at ambient temperature, but direct line-of-sight access to light source is required which limits application in multilayer structures

Engineering Contradiction:

Improvecuring accessibilityVSAvoidapplication scope

Core Design Contradiction:

Ease of operationVSAdaptability or versatility

Solution Approach 1:

The patent introduces an intermediary substance (phosphor or scintillator material) that converts ionizing radiation into visible light, enabling photoinitiation in locations where direct light access is impossible. This mediator allows the curing process to occur deep within multilayer structures by converting penetrating radiation into the specific wavelength needed by the photoinitiator.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent replaces the conventional UV light source system with an ionizing radiation-based system. Instead of using external UV lamps that require line-of-sight access, the system uses ionizing radiation (X-rays or gamma rays) that can penetrate deep into structures, combined with phosphor materials that convert this radiation into the appropriate wavelength for photopolymerization.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Reliability

If thermoset adhesives are cured by heating, then polymerization can be achieved, but thermal expansion mismatch causes stress and warpage issues

Engineering Contradiction:

Improvebonding qualityVSAvoidthermal stress

Core Design Contradiction:

ReliabilityVSStress or pressure

Solution Approach 1:

The patent changes the curing parameter from thermal energy to photonic energy. By using photoinitiation triggered by ionizing radiation conversion, the process occurs at or near ambient temperature, eliminating the thermal expansion mismatch that causes stress and warpage in conventional heat-cured adhesives.

Inventive Principle:

Principle #35Parameter changes

3Manufacturing precision

If UV light is used for curing adhesives, then polymerization can be initiated, but the light cannot penetrate into the interior of multilayer stacks

Engineering Contradiction:

Improvecuring completenessVSAvoidadhesive bead volume

Core Design Contradiction:

Manufacturing precisionVSVolume of moving object

Solution Approach 1:

The patent uses phosphor or scintillator materials as intermediaries that are distributed throughout the adhesive formulation. These materials absorb ionizing radiation throughout the entire volume and convert it to visible light locally, enabling uniform curing throughout the bulk of the adhesive without requiring light penetration from the surface.

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

Enables curing of adhesives within the entire volume of the adhesive bead, regardless of line-of-sight access, and reduces thermal stress by allowing bonding at ambient temperatures, improving the reliability and efficiency of adhesive applications in microelectronics and other fields.

Implementation Method 1

an energy converting material selected to emit said wavelength of light when exposed to ionizing radiation

Methodology Applied

Scientific EffectScintillation: Scintillation

Implementation Method 2

at least one photo-initiator responsive to a selected wavelength of light

Methodology Applied

Scientific EffectPhotopolymerisation: Photopolymerisation

Data Source

PatentUS11901331B2Adhesive bonding composition and electronic components prepared from the same

Publication Date: 2024.02.13 IMMUNOLIGHT LLC

AI summary

A polymerizable composition includes at least one monomer, a photoinitiator capable of initiating polymerization of the monomer when exposed to light, and a phosphor capable of producing light when exposed to radiation (typically X-rays). The material is particularly suitable for bonding components at ambient temperature in situations where the bond joint is not accessible to an external light source. An associated method includes: placing a polymerizable adhesive composition, including a photoinitiator and energy converting material, such as a down-converting phosphor, in contact with at least two components to be bonded to form an assembly; and, irradiating the assembly with radiation at a first wavelength, capable of conversion (down-conversion by the phosphor) to a second wavelength capable of activating the photoinitiator, to prepare items such as inkjet cartridges, wafer-to-wafer assemblies, semiconductors, integrated circuits, and the like.