Silver Joining Material Viscosity Control for Void-Free Bonding
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Solution Overview
Problem
Existing methods for joining conductive components using silver-based joining materials face issues with void generation and reduced electrical conductivity and strength due to shifting during transportation or drying processes, leading to unsatisfactory bonding results.
Innovation Solution
A joining material with specific viscosity and particle size distribution, including silver particles, is used to form a joining portion by attaching to one conductive component, laminating, drying, and firing, which suppresses void generation and enhances conductivity and strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If a member to be joined is placed on pre-fired joining material in a dried or semi-dried state, then the joining material can be prepared in advance, but the member to be joined is not sufficiently fixed and may shift during transportation
Solution Approach 1:
The joining material is applied to the conductive component and allowed to remain in a wet or semi-dried state during transportation, performing the positioning action in advance before firing. This preliminary positioning is maintained because the material has not yet undergone complete drying and firing, thus avoiding shift during transport while enabling pre-positioning.
Solution Approach 2:
Instead of the conventional approach of drying or semi-drying the joining material before placing the component (which causes shifting), the invention inverts the sequence by placing the component on wet or semi-dried material and then drying/firing together. This reversal eliminates the positioning problem while achieving fixation.
2Manufacturing precision
If a conductive component is placed on undried joining material and then dried and fired, then positioning accuracy is improved, but voids are generated between the component and joining material
Solution Approach 1:
The invention changes the viscosity parameter of the joining material by controlling particle size (D50: 0.15-0.8 μm) and viscosity (70 Pa·s or greater). These parameter changes enable the material to maintain positioning accuracy during drying while preventing void formation through appropriate rheological properties that accommodate component placement and subsequent drying without air entrapment.
3Reliability
If the joining material has high viscosity and specific particle size, then void generation is suppressed, but the material may be difficult to apply
Solution Approach 1:
The invention optimizes specific parameters including viscosity (70 Pa·s or greater) and particle size distribution (D50: 0.15-0.8 μm) to achieve a balance between ease of application and void prevention. These parameter changes ensure the material remains workable during application while preventing void formation during the subsequent drying and firing processes.
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 proposed method effectively prevents voids in the joining portion, improving electrical conductivity and strength by using a joining material with controlled viscosity and particle size distribution, ensuring stable bonding of conductive components.
Implementation Method 1
drying the joining material in the laminate to form a dried joining material
Implementation Method 2
firing the dried joining material at a temperature higher than a temperature at which the joining material has been dried to thereby form the joining portion from the dried joining material
Data Source
Figure 1~2E
Figure 3A~3E
AI summary
A joining material includes: metal particles containing metal particles (a); and a solvent for dispersing the metal particles, wherein the joining material has a viscosity, as measured according to JIS Z 3285:2017, of 70 Pa·s or greater, and the metal particles (a) have a particle size D50 at a cumulative volume of 50%, as measured by laser diffraction/scattering particle size distribution measurement, of greater than 0.15 µm and less than 0.8 µm.