Core-Shell Metal Nanoparticles for Low-Temperature 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, necessitating the development of alternative materials with high electrical and thermal conductivity.
Innovation Solution
A sintering powder comprising a copper core coated with a silver shell, which offers high electrical and thermal conductivity while reducing oxidation and manufacturing costs, allowing for low-temperature sintering with minimal pressure, thus forming strong and reliable joints.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If noble metal nanoparticles (silver, gold) are used for high thermal conductivity and nonoxidizing properties, then electrical and thermal performance is improved, but manufacturing cost increases significantly
Solution Approach 1:
The patent uses composite core-shell nanoparticles where a copper core provides high electrical and thermal conductivity at low cost, while a silver shell provides oxidation resistance and maintains surface conductivity. This composite structure combines the advantages of both materials to achieve noble metal performance at reduced cost.
Solution Approach 2:
The silver shell is applied only as a thin coating on the copper core surface, providing oxidation protection and surface conductivity where needed, while the bulk copper core provides the majority of the thermal and electrical conduction pathways. This local application of expensive material optimizes cost-performance ratio.
2Ease of manufacture
If conventional lead-based solder paste is used for die attachment, then ease of manufacture is improved, but high-temperature operation reliability deteriorates due to solder joint fatigue and intermetallic compound growth
Solution Approach 1:
The patent changes the material composition from traditional lead-based solder to copper-silver core-shell nanoparticles, fundamentally altering the thermal and mechanical properties to enable high-temperature operation while maintaining manufacturability through sintering processes.
3Strength
If high sintering temperature is applied to achieve strong joints, then joint strength is improved, but circuit damages and die level stresses increase
Solution Approach 1:
The nanoparticle structure enables sintering at lower temperatures compared to bulk materials due to higher surface energy and reduced diffusion distances, achieving strong joints while avoiding thermal damage to sensitive electronic components.
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 at lower temperatures and pressures, enhancing the reliability and cost-effectiveness of semiconductor packaging.
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
Sintered joints are formed by atomic diffusion of metal particles placed between two work pieces to be joined
Implementation Method 4
Nanoparticles of several elements including gold, palladium, silver and copper have been well-studied due to their potential applications as conducting materials
Implementation Method 5
Noble metal nanoparticles such as silver and gold, because of their high thermal conductivity and excellent nonoxidizing properties
Data Source
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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; and a shell at least partially coating the core, the shell comprising a second material having a lower oxidation potential than the first material.