Copper Paste Bonding Material Void Suppression
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Solution Overview
Problem
The existing bonding materials using fine silver particles are expensive and prone to void formation, leading to reliability issues due to stress concentration at voids during thermal cycles, which compromises the bonding strength.
Innovation Solution
A copper paste bonding material with a copper powder average particle diameter of 0.1 to 1 µm and an alcohol solvent content of 5% to 20% by weight, providing a viscosity of 150 Pa·s or less, is used to bond articles via a copper bonding layer, reducing void formation and increasing shear strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the content of metal particles in the bonding material is increased, then the cost is reduced and bonding strength is improved, but the viscosity of the bonding material is increased making it difficult to print
Solution Approach 1:
The patent changes the particle size parameter of copper powder to 0.1-1 μm (specifically 0.3-0.5 μm in embodiments), which allows achieving high metal content (80-90 wt%) while maintaining acceptable viscosity for screen printing. The fine particle size reduces aggregation and improves flow characteristics despite high solid content.
Solution Approach 2:
The patent replaces expensive fine silver particles with inexpensive copper particles, achieving cost reduction while maintaining bonding functionality. Copper is significantly cheaper than silver, allowing higher metal content in the paste without proportionally increasing cost.
2Quantity of substance
If the content of solvent in the bonding material is decreased, then the content of metal particles is increased, but the viscosity of the bonding material is increased making it difficult to apply by screen printing
Solution Approach 1:
The patent optimizes the particle size parameter of copper powder to 0.1-1 μm, which fundamentally changes the rheological properties of the paste. This particle size range allows achieving 80-90 wt% metal content while maintaining viscosity at 150 Pa·s or less, enabling screen printing application.
3Reliability
If voids exist on the bonded surfaces, then stress is applied to the portions of the voids during cooling/heating cycles, but cracks are formed in the bonding layer from the voids deteriorating the reliability of bonding
Solution Approach 1:
The patent optimizes copper particle size to 0.1-1 μm and controls metal content at 80-90 wt%, which improves paste flow and filling characteristics during screening and bonding. This reduces void formation in the bonded joints, eliminating stress concentration points that would lead to crack propagation during thermal cycling.
Solution Approach 2:
The patent uses alcohol-based solvent system that provides appropriate wetting and flow characteristics, allowing the paste to fully fill the screen mesh and bonding area, minimizing air entrapment and void formation during the bonding process.
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 copper paste bonding material allows for reliable bonding with minimal voids and high shear strength, achieving a bonding solution that is cost-effective and printable, while maintaining structural integrity under thermal cycles.
Implementation Method 1
heating the bonding material to sinter copper therein to form a copper bonding layer to bond the articles to each other
Data Source
AI summary
There is provided an inexpensive bonding material, which can be easily printed on articles to be bonded to each other and which can suppress the generation of voids in the bonded portions of the articles to be bonded to each other, and a bonding method using the same. In a bonding material of a copper paste which contains a copper powder containing 0.3 % by weight or less of carbon and having an average particle diameter of 0.1 to 1 µm, and an alcohol solvent, such as a monoalcohol, a diol, a triol or a terpene alcohol, the content of the copper powder is in the range of from 80 % by weight to 95 % by weight, and the content of the alcohol solvent is in the range of from 5 % by weight to 20 % by weight.