Capped Nano Copper Paste for Low-Temperature Sintered Die Attach
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Solution Overview
Problem
Current sintering technologies for electronics face challenges with high sintering temperatures, cost issues due to silver usage, and ion migration problems, particularly with silver nanoparticles, while copper nanoparticles are prone to oxidation, limiting their application in conductive die attach pastes.
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 sintering temperatures, providing equivalent benefits to nanosilver with lower costs and preventing ion migration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If silver nanoparticles are used for sintering, then electrical and thermal conductivity is improved, but cost increases and ion migration occurs at high temperature and humidity
Solution Approach 1:
The patent replaces expensive silver nanoparticles with copper nanoparticles, which are significantly cheaper while providing comparable electrical and thermal conductivity. The copper particles are used in a disposable paste form that is screen-printed and sintered to form permanent conductive paths, eliminating the need for expensive silver materials.
Solution Approach 2:
The patent changes the material parameter from silver to copper, and controls particle size parameters (D10 ≥ 100 nm and D90 ≤ 2000 nm) to optimize performance. This parameter change allows copper to achieve conductivity levels comparable to silver while avoiding ion migration issues through proper particle size control and sintering process optimization.
2Object-generated harmful factors
If copper nanoparticles are used to reduce cost, then material cost decreases, but oxidation resistance worsens
Solution Approach 1:
The patent applies preliminary protective action by coating copper particles with organic capping agents during particle synthesis. This preliminary protection prevents oxidation during storage and handling, and the capping agents are subsequently removed during the sintering process, leaving clean copper particles for sintering while having already protected against oxidation during the critical manufacturing and storage phases.
Solution Approach 2:
The patent creates an inert environment by using organic capping agents that form protective layers around copper particles, effectively isolating them from oxygen during storage and handling. The sintering process is also conducted in a controlled atmosphere that prevents oxidation, allowing copper particles to be processed without encountering harmful oxidative conditions.
3Temperature
If high pressure is applied during sintering, then sintering temperature decreases, but automation difficulty increases and work piece damage occurs
Solution Approach 1:
The patent changes the sintering parameters by using smaller copper particles with controlled size distribution (D10 ≥ 100 nm and D90 ≤ 2000 nm). These smaller particles have higher surface area to volume ratios, which increases their reactivity and allows sintering to occur at lower temperatures without requiring high pressure, thereby maintaining ease of automation and preventing work piece damage.
Solution Approach 2:
The patent employs mechanical vibration during the sintering process to enhance particle contact and diffusion at lower temperatures. The vibration energy promotes particle rearrangement and bonding without requiring high pressure, enabling low-temperature sintering while maintaining processability and avoiding work piece damage.
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 enables efficient, cost-effective, and oxidation-resistant sintering with improved mechanical, thermal, and electrical conductivity, suitable for diverse surface joins, including copper-to-copper and copper-to-aluminum, while being air-stable and non-agglomerated, thus overcoming the limitations of silver and conventional copper powders.
Implementation Method 1
the inherent tendency of copper nanoparticles to oxidize is still a major problem... copper nanoparticles can resist oxidation under ambient conditions if they are coated by a proper protective layer
Implementation Method 2
A typical method of forming a sintered joint involves placing a metal powder, often in the form of a powder compact, between two work pieces to be joined and then sintering the metal powder. The resulting atomic diffusion of the metal atoms forms a bond between the two work pieces
Implementation Method 3
Sintered joints formed by atomic diffusion of silver nanoparticles can be processed at a temperature significantly lower than the melting temperature of the bulk
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.