Capped Copper Sintering Powder for Low-Temperature Die Attach
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Solution Overview
Problem
Current sintering technologies using silver nanoparticles face high sintering temperatures, cost issues due to silver's high price, and ion migration problems, while copper nanoparticles are prone to oxidation, limiting their application in electronics for die attach applications.
Innovation Solution
A sintering powder comprising copper particles coated with a capping agent, exhibiting a specific particle size distribution (D10 ≥ 100 nm and D90 ≤ 2000 nm), which reduces oxidation and allows for lower temperature sintering, providing equivalent benefits to nanosilver in conductivity and mechanical properties at a lower cost, and enabling versatile joining of different surface finishes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If copper nanoparticles are used as sintering powder, then cost is reduced and ion migration problem is eliminated, but oxidation resistance deteriorates
Solution Approach 1:
The patent uses composite materials by combining copper particles with a protective coating layer. The coating material (such as organic compounds, polymers, or inorganic materials) forms a composite structure that protects the copper particles from oxidation while maintaining their electrical and thermal conductivity properties. This resolves the contradiction by integrating two materials with complementary properties: copper for conductivity and coating for oxidation resistance.
Solution Approach 2:
The patent creates an inert protective environment around copper particles through coating materials that form barrier layers. These coatings prevent direct contact between copper and oxygen, effectively creating a localized inert atmosphere that protects against oxidation. This approach allows copper to maintain its superior conductivity properties without suffering from oxidation degradation.
2Reliability
If silver nanoparticles are used for sintering, then electrical and thermal conductivity is improved, but cost increases
Solution Approach 1:
The patent replaces expensive silver nanoparticles with cheaper copper particles that can achieve similar performance outcomes. The protective coating extends the effective lifetime of copper particles by preventing oxidation, making them a cost-effective alternative to silver. This principle is applied by substituting a high-cost material (silver) with a low-cost material (copper) while using the coating to maintain performance over time.
Solution Approach 2:
The patent changes the material parameter from silver to copper, which has lower cost but potentially different oxidation behavior. By adjusting other parameters (adding protective coatings, controlling particle size, optimizing sintering conditions), the patent maintains the desired electrical conductivity while reducing material cost. This demonstrates parameter changes by modifying material composition and protective measures rather than changing the fundamental copper-to-silver substitution.
3Temperature
If high pressure is applied during sintering, then sintering temperature is reduced, but process automation becomes difficult and work pieces may be damaged
Solution Approach 1:
The patent changes the sintering parameters by using copper particles with specific size distributions (D10 ≥ 100 nm and D90 ≤ 2000 nm) and protective coatings, which enable effective sintering at lower temperatures compared to conventional materials. The protective coating facilitates lower temperature processing by preventing oxidation during sintering, allowing the use of milder thermal conditions that are more compatible with automated processes and sensitive substrates.
Solution Approach 2:
The protective coating acts as an intermediary substance that enables lower temperature sintering by preventing direct oxidation of copper particles. This intermediary layer allows the sintering process to proceed at reduced temperatures without compromising the integrity of the copper particles or the work pieces, thereby facilitating automation and reducing the risk of damage.
4Quantity of substance
If copper particles are used without protective coating, then cost is reduced, but oxidation resistance deteriorates
Solution Approach 1:
The patent creates a composite structure by coating copper particles with protective materials. This composite approach maintains the low cost advantage of copper while adding a thin protective layer that prevents oxidation. The coating material constitutes a small fraction of the total material cost but provides critical protection, achieving a cost-effective balance between material expense and oxidation resistance.
Solution Approach 2:
The patent applies thin film coatings on copper particles to provide oxidation protection. These thin films form flexible protective shells that prevent oxygen access to the copper surface without significantly increasing material cost or particle size. The thin film approach maintains cost effectiveness while providing adequate protection against oxidation during storage and processing.
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 sintering powder is air-stable, non-agglomerated, and offers improved sinterability, thermal, and electrical conductivity with reduced ion migration, making it suitable for die attach applications and versatile surface joining, while being cost-effective and resistant to oxidation.
Implementation Method 1
the inherent tendency of copper nanoparticles to oxidize is still a major problem... copper particles coated with a capping agent... resistant to oxidation
Implementation Method 2
The resulting atomic diffusion of the metal atoms forms a bond between the two work pieces
Implementation Method 3
sintering the metal powder... sintering powder comprising copper particles
Implementation Method 4
copper also possesses a very high conductivity... improved sinterability, thermal, and electrical conductivity
Implementation Method 5
copper also possesses a very high conductivity (only 6% less than that of Ag)... improved sinterability, thermal, and electrical conductivity
Data Source
AI summary
A sintering powder comprising copper particles, wherein: the particles are at least partially coated with a capping agent, and the particles exhibit a D10 of greater than or equal to 100 nm and a D90 of less than or equal to 2000 nm.