Sn-Ni-Fe Preform Solder for Low-Void High-Temperature Joints
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Solution Overview
Problem
Existing soldering technologies face challenges in suppressing void formation and ensuring bonding strength under high temperature conditions, particularly with silicon carbide power semiconductor elements, due to issues like flux volatility, oxide film formation, and reduced fluidity, leading to inferior reliability and increased risk of cracks.
Innovation Solution
A preform solder with a metal structure comprising a continuous phase of Sn and a dispersed phase of a Ni-Fe alloy, where the Sn phase has a melting point of 250 °C or less and the Ni-Fe alloy has a melting point exceeding 250 °C, optimized in composition and particle size to minimize voids and enhance bonding strength through intermetallic compound formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If TLP paste containing flux is used for soldering, then soldering can be performed, but flux volatilizes during melting and cavities remain in the solder, causing voids
Solution Approach 1:
The invention removes the flux component from the solder paste formulation, extracting the harmful element that causes volatilization and void formation. The solder paste consists only of solder powder and organic vehicle without any flux, eliminating the source of the problem while maintaining soldering functionality.
Solution Approach 2:
The invention changes the compositional parameters of the solder paste by defining specific ranges for solder powder particle size (3-50 μm) and the ratio of solder powder to organic vehicle (95:5 to 5:95 by mass). These parameter adjustments optimize the paste properties for void-free soldering without requiring flux.
2Reliability
If heating temperature is increased to improve fluidity and release cavities, then cavity release may improve, but thermal damage to semiconductor element occurs
Solution Approach 1:
The invention performs preliminary action by optimizing the solder paste composition before heating occurs. The specific particle size range and paste formulation are designed in advance to ensure proper fluidity and cavity release at moderate temperatures, eliminating the need for high-temperature processing that would cause thermal damage.
Solution Approach 2:
The invention changes the physical parameters of the solder paste, specifically controlling particle size distribution (3-50 μm) and paste composition ratios, to achieve optimal flow characteristics at lower heating temperatures. This allows cavity release without exceeding thermal damage thresholds for semiconductor elements.
3Object-affected harmful factors
If heating temperature is lowered and heating time is lengthened to prevent thermal damage, then thermal damage is reduced, but fluidity is not improved and voids occur
Solution Approach 1:
The invention changes the compositional parameters of the solder paste to achieve optimal viscosity and fluidity characteristics. By controlling solder powder particle size (3-50 μm) and the ratio of solder powder to organic vehicle, the paste maintains proper flow properties at lower heating temperatures, enabling cavity release without thermal damage and preventing void formation.
4Stability of the object's composition
If strong oxide film is formed on solder powder surface during heating, then oxidation protection occurs, but oxide film is not reduced and solder powders cannot fuse, causing cavities and voids
Solution Approach 1:
The invention removes flux from the paste formulation, which eliminates the reducing environment that would otherwise be needed to reduce oxide films. Instead, the invention relies on the organic vehicle to provide controlled oxidation resistance without forming problematic oxide films on the solder powder surfaces, enabling proper fusion without cavities or voids.
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 solution effectively reduces void occurrence and increases shear strength in solder joints, improving thermal reliability and bonding quality under high temperature conditions without the use of flux, thereby enhancing the performance and durability of solder joints.
Implementation Method 1
a melting point of the metal that composes the first phase is 250 °C or less
Implementation Method 2
enhance bonding strength through intermetallic compound formation
Data Source
Figure 1~2
AI summary
Provided is a preform solder including a first metal containing Sn and a second metal formed of an alloy containing Ni and Fe. Alternatively, provided is a preform solder (1) having a metal structure including a first phase (10) that is a continuous phase and a second phase (20) dispersed in the first phase (10), the first phase (10) contains Sn, the second phase (20) is formed of an alloy containing Ni and Fe, and a grain boundary (15) of a metal is present in the first phase (10).