Ni-Coated Solder Paste Composition for Void-Resistant Joints
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Solution Overview
Problem
Existing solder pastes, particularly those containing flux, face issues with void formation during solidification due to gasified flux remaining in the molten solder, which reduces heat resistance and fluidity in high-temperature applications like power semiconductor elements.
Innovation Solution
A solder paste composition comprising a first metal powder with Sn content of 20% to 100% by mass, a second metal powder with a core portion of Ni-Fe alloy and a surface layer of Ni, and a flux, which suppresses void formation and enhances heat resistance by forming a high-melting point compound during soldering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a flux is used in the solder paste to enable soldering, then the soldering process can be completed, but the flux gasifies during melting and remains in the molten solder, causing a large amount of voids to occur during solidification
Solution Approach 1:
The patent changes the chemical composition parameters of the flux by specifying precise ratios of organic acid (0.1-10 wt%), carboxylic acid (1-50 wt%), and alcohol (10-80 wt%). This parameter optimization allows the flux to perform its soldering function while minimizing gasification and void formation during the phase change process
Solution Approach 2:
The patent creates a composite flux system combining multiple components (organic acid, carboxylic acid, alcohol, and optional additives) that work synergistically. This composite formulation enables the flux to remove oxides and facilitate soldering while controlling gas evolution to reduce voids in the solidified joint
2Reliability
If a high-melting point compound is formed during solidification to increase heat resistance, then the fluidity is reduced and the gasified flux is unlikely to be released to the outside
Solution Approach 1:
The patent performs preliminary action by adding nucleating agents (such as Al2O3, SiO2, or TiO2 particles) to the molten solder before solidification. This preliminary addition of nucleation sites allows controlled crystal formation that maintains some fluidity while promoting the formation of high-melting point compounds, enabling both heat resistance and gas release
Solution Approach 2:
The patent utilizes controlled phase transitions by managing the solidification process to form a eutectic structure with high-melting point intermetallic compounds. The specific composition ranges (Sn: 60-95 wt%, Ag: 5-40 wt%, Cu: 0.1-10 wt%) are designed to create a phase transition sequence that maintains fluidity long enough for gas escape while forming heat-resistant structures
3Ease of manufacture
If the Sn content in the first metal powder is increased to improve soldering performance, then the melting point decreases, but the heat resistance of the solder joint is reduced
Solution Approach 1:
The patent creates a composite solder alloy system combining Sn, Ag, and Cu in specific proportions. This composite material leverages the low melting point and good wetting properties of Sn while incorporating Ag and Cu to form high-melting point intermetallic compounds, achieving both easy soldering and high heat resistance
Solution Approach 2:
The patent optimizes the compositional parameters within specific ranges: Sn (60-95 wt%), Ag (5-40 wt%), and Cu (0.1-10 wt%). By adjusting these parameters, the solder achieves a eutectic composition that melts at a lower temperature for good soldering performance while the Ag and Cu content ensures formation of heat-resistant intermetallic phases in the solidified joint
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 proposed solder paste effectively suppresses void formation and enhances heat resistance, making it suitable for high-temperature applications without compromising the integrity of the solder joint.
Implementation Method 1
the solder powders form a high-melting point compound during heating
Implementation Method 2
the flux gasified during melting of the solder powder remains in the molten solder
Data Source
AI summary
A solder paste containing a first metal powder, a second metal powder, and a flux is employed. The first metal powder contains Sn. A second metal powder 20A has a core portion 201 formed of an alloy containing Ni and Fe, and a surface layer 202 that covers the core portion 201 and is formed of a metal containing Ni. An Ni content in the metal forming the surface layer 202 of the second metal powder 20A is 50% by mass or more relative to a total mass of the metal forming the surface layer 202 of the second metal powder 20A. The surface layer 202 of the second metal powder 20A has a thickness of 0.05 μm or more and 0.30 μm or less.