Core-Shell Sintering Powder for Oxidation-Resistant Die Attach
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Solution Overview
Problem
Current lead-free die attach materials face limitations in high temperature operations, leading to solder joint fatigue and reliability issues due to intermetallic compound growth, and are costly, with noble metal nanoparticles being expensive and copper nanoparticles prone to oxidation.
Innovation Solution
A sintering powder with a core-shell structure, where the core is a low-cost, high-conductivity material like copper and the shell is a noble metal with lower oxidation potential, such as silver, reducing oxidation and allowing for low-temperature sintering with minimal pressure, thereby enhancing electrical and thermal conductivity while minimizing manufacturing costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If copper nanoparticles are used to replace noble metal nanoparticles, then manufacturing cost is reduced and electrical conductivity is improved, but oxidation resistance deteriorates
Solution Approach 1:
The invention uses a core-shell composite structure where copper nanoparticles form the core and provide high electrical conductivity and low cost, while a protective shell material forms the outer layer and provides oxidation resistance. This composite structure combines the advantages of both materials to achieve reliable die attach performance.
Solution Approach 2:
The shell material acts as an intermediary protective layer between the copper core and the oxidizing environment. This intermediate layer prevents direct contact between oxygen and the copper surface, thereby preventing oxidation while allowing the copper core to maintain its electrical conductivity function.
2Ease of manufacture
If conventional lead-based solder paste is used, then ease of manufacture is maintained, but high temperature operation capability deteriorates due to solder joint fatigue
Solution Approach 1:
The invention changes the material parameters by using metal nanoparticles with specific size distributions and surface properties that enable low-temperature sintering. This allows the formation of strong metallurgical bonds at temperatures below 200°C, avoiding the high-temperature limitations of conventional solders while maintaining ease of manufacture through simple paste formulation and application processes.
3Reliability
If noble metal nanoparticles are used, then electrical and thermal conductivity are improved, but manufacturing cost increases
Solution Approach 1:
The invention applies local quality by concentrating the expensive noble metal shell material only at the surface where oxidation protection is needed, while the bulk of the particle (the core) is made of inexpensive copper. This localized use of noble metal minimizes cost while maintaining the electrical and thermal conductivity benefits.
4Strength
If high pressure is applied during sintering, then bonding strength is improved, but device complexity and processing difficulty increase
Solution Approach 1:
The invention utilizes phase transition mechanisms at the nanoscale level, where the high surface energy of nanoparticles enables solid-state diffusion and bonding at low temperatures without requiring high pressure. The nanoparticles undergo structural reorganization and coalescence through thermal activation alone, simplifying the sintering process while achieving strong bonds.
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 sintering powder achieves high electrical and thermal conductivity with reduced susceptibility to oxidation, enabling strong and reliable sintered joints suitable for electronic applications without the need for high pressures or temperatures, thus improving the reliability and cost-effectiveness of die attachment processes.
Implementation Method 1
a shell at least partially coating the core, the shell comprising a second material having a lower oxidation potential than the first material
Implementation Method 2
Nanoparticles have high surface energy which enables them to undergo particle coalescence at a much lower processing temperature as compared to the bulk materials
Implementation Method 3
A sintering temperature well below the melting point for nanoscale metals is of great advantage for semiconductor packaging
Data Source
AI summary
A sintering powder, wherein a least a portion of the particles making up the sintering powder comprise:a core comprising a first material; anda shell at least partially coating the core, the shell comprising a second material having a lower oxidation potential than the first material.