Conductive Paste Bimodal Particle Distribution for Thermal Stress Resistance
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Solution Overview
Problem
Conductive connecting members, such as bumps and die bonding portions, face issues with thermal stress resistance and mechanical strength due to variations in particle size and the formation of voids and cracks during the sintering process, leading to reduced reliability and lifespan in semiconductor devices.
Innovation Solution
A conductive paste is developed with a specific ratio of metal fine particles (1-150 nm) and larger particles (1-10 μm) mixed with an organic solvent, which prevents coarse void formation and enhances bonding strength by controlling particle distribution and sintering conditions, resulting in a porous body with improved thermal cycle characteristics and mechanical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If plating process is used to form bumps, then fine patterned bumps can be formed with controlled height, but the bumps have poor thermal stress resistance and are prone to breakage due to excessive strain from applied pressure
Solution Approach 1:
The patent uses porous metal particles as the base material for conductive paste. These porous particles provide inherent compliance and stress absorption capability, allowing the bump to deform under pressure without accumulating excessive strain. The porous structure acts as a buffer that mitigates thermal stress and mechanical strain, resolving the contradiction between achieving precise bump formation and maintaining thermal stress resistance.
Solution Approach 2:
The conductive paste comprises a composite system with porous metal particles as the base material and fine metal particles filling the voids. This composite structure combines the compliance and stress absorption of porous material with the density and conductivity of fine particles, creating a bump that simultaneously achieves good manufacturability, thermal stress resistance, and electrical conductivity.
2Strength
If porous body is used to reduce strain and improve thermal stress resistance, then crack resistance improves, but coarse voids and cracks may form during sintering process
Solution Approach 1:
The patent employs a nested particle structure where fine metal particles are positioned within the voids of porous metal particles. This nested arrangement ensures that fine particles fill the spaces between larger porous particles during sintering, preventing the formation of coarse voids and cracks while maintaining the stress absorption benefits of the porous structure.
Solution Approach 2:
The conductive paste exhibits local quality variation with different particle sizes distributed in specific regions. Porous metal particles provide the overall structure and stress absorption, while fine metal particles locally fill voids and enhance density in critical areas. This localized particle distribution prevents coarse void formation while maintaining crack resistance throughout the sintered bump.
3Manufacturing precision
If only fine metal particles (1-150 nm) are used in conductive paste, then good filling properties are achieved, but coarse voids and cracks form during sintering due to particle aggregation
Solution Approach 1:
The patent segments the particle size distribution into two distinct populations: porous metal particles (1-10 μm) and fine metal particles (1-150 nm). This segmentation allows each particle size to perform its specific function - porous particles provide structural framework and prevent aggregation, while fine particles fill voids and enhance density. The segmented structure prevents coarse void formation and improves crack resistance.
Solution Approach 2:
The patent changes the particle size parameter by using a bimodal distribution instead of a single size population. The porous metal particles with larger size (1-10 μm) serve as spacers that prevent fine particle aggregation, while the fine particles (1-150 nm) provide good filling properties. This parameter variation resolves the contradiction between uniform particle distribution and crack resistance.
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 solution provides enhanced bonding strength, crack resistance, and thermal cycle characteristics, ensuring reliable electrical and mechanical connections in semiconductor devices by preventing voids and cracks, thus improving the durability and performance of conductive connecting members.
Implementation Method 1
a porous body is known, which is formed by sintering the conductive paste containing metal fine particles
Data Source
AI summary
Providing the conductive paste for the material forming the conductive connecting member without disproportionately located holes (gaps), coarse voids, and cracks, which improves thermal cycle and is excellent in crack resistance and bonding strength. An conductive paste including metal fine particles (P) comprising metal fine particles (P1) of one or more than two kinds selected from metal and alloy thereof, having mean primary particle diameter from 1 to 150 nm, and metal fine particles (P2) of same metal as the metal fine particles (P1), having mean primary particle diameter from 1 to 10 μm, mixing ratio of (P1/P2) being from 80 to 95 mass % for P1 and from 20 to 5 mass % for P2 (a total of mass % being 100 mass %); and organic dispersion medium (D) comprising organic solvent (S), or organic solvent (S) and organic binder (B), mixing ratio (P/D) of the metal fine particles (P) and the organic dispersion medium (D) being from 50 to 85 mass % for P and from 50 to 15 mass % for D (a total of mass % being 100 mass %).