Lead-Free Solder Paste for Thermal Fatigue Resistance
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Solution Overview
Problem
Existing methods for connecting electronic components to substrates in microelectronics face challenges with thermal fatigue due to the limitations of lead-free solder pastes, which lack sufficient resistance to periodic temperature fluctuations and mechanical load, and require improvements in thermal and electrical conductivity.
Innovation Solution
A method using a solder paste with 10-30% copper particles, 60-80% tin or tin-copper alloys, and 3-30% flux, where the average particle diameter is ≤15 μm, forming a contact layer with a eutectic and intermetallic phase ratio of 5-50% by weight, allowing for increased thickness and stability through isothermal solidification and intermetallic phase formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If lead-free solder pastes with large particle diameter (25-45 μm) are used, then the connection provides sufficient resistance to thermal fatigue, but the contact layer has limited thermal and mechanical load capacity due to sandwich structure formation
Solution Approach 1:
The patent changes the particle diameter parameter from 25-45 μm to ≤15 μm, which fundamentally alters the solidification process. This parameter change enables the formation of a homogeneous contact layer with interspersed intermetallic phases throughout the eutectic structure, rather than the sandwich structure formed by larger particles, thereby improving thermal and mechanical load capacity while maintaining thermal fatigue resistance
Solution Approach 2:
The patent creates a composite contact layer structure where intermetallic phases are distributed within the eutectic phase matrix. This composite structure combines the advantages of both phases: the eutectic phase provides thermal fatigue resistance while the interspersed intermetallic phases enhance thermal and mechanical load capacity, resolving the contradiction between these two requirements
2Strength
If diffusion soldering is used to create high-temperature-resistant contact layers, then the contact layer contains only intermetallic phases with high strength, but the thickness must be increased to achieve sufficient strength, complicating the process
Solution Approach 1:
The patent merges the advantages of fusion soldering (eutectic phase formation) and diffusion soldering (intermetallic phase formation) into a single process. By using fine particles (≤15 μm) that melt and solidify to form eutectic structure with interspersed intermetallic phases, the method achieves high strength without requiring the complex multi-step process of traditional diffusion soldering, thereby reducing device complexity while maintaining strength
3Reliability
If lead-containing solder pastes are used, then the connection has sufficient stability against thermal fatigue, but lead-free alternatives are required by directive 2002/95/EC
Solution Approach 1:
The patent changes the compositional parameters of the solder paste to be lead-free while maintaining thermal fatigue resistance by optimizing the particle diameter (≤15 μm) and creating a specific microstructure with interspersed intermetallic phases within the eutectic structure. This parameter optimization allows lead-free solder to achieve performance comparable to or exceeding lead-based solder, eliminating the harmful lead content while preserving reliability
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 method achieves a significant increase in strength and stability of the contact layer, enhancing thermal resistance and conductivity without reducing thermal and electrical performance, addressing the limitations of previous lead-free solder pastes and diffusion soldering techniques.
Implementation Method 1
the contact layer having a proportion of eutectic phase and a proportion of intermetallic phase
Implementation Method 2
forming a contact layer with a eutectic and intermetallic phase ratio of 5-50% by weight
Implementation Method 3
allowing for increased thickness and stability through isothermal solidification and intermetallic phase formation
Implementation Method 4
enhancing thermal resistance and conductivity without reducing thermal and electrical performance
Implementation Method 5
enhancing thermal resistance and conductivity without reducing thermal and electrical performance
Data Source
AI summary
The invention relates to a simple method for cohesively joining an electronic component to a substrate, wherein a) an electronic component with a first surface to be joined and a substrate with a second surface to be joined is provided, b) a soldering paste is applied to at least one of the surfaces to be joined, c) the electronic component and the substrate are arranged in such a way that the first surface of the electronic component to be joined is in contact to the second surface to be joined via the soldering paste and d) the arrangement from c) is soldered in order to create a cohesive joint between the electronic component and the substrate, wherein the soldering paste (i) comprises 10-30 wt % of copper particles, (ii) 60-80 wt % of particles of at least one material chosen from the group comprising tin and tin-copper-alloys and (iii) 3-30 wt% of flux material, wherein the median particle diameter of the copper particles and the particles from a material chosen from the group comprising tin and tin-cooper-alloys is not more than 15 μm and wherein the application thickness of the soldering paste is at least 20 μm.