Ni-Fe Preform Solder Structure for Low-Void High-Temperature Joints
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Solution Overview
Problem
Existing soldering technologies face challenges in minimizing voids and ensuring strong bonding under high temperature conditions, particularly with silicon carbide power semiconductor elements, due to issues like flux volatility, oxide film formation, and reduced bonding strength.
Innovation Solution
A preform solder composed of a first metal containing Sn and a second metal alloy with Ni and Fe, where the second metal's content is 5 to 70 mass % and has a particle size of 0.1 to 1000 μm, is used, along with a manufacturing method involving mixing and rolling to create a metal structure with a continuous phase and dispersed phase, minimizing voids and enhancing shear strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a TLP paste containing flux is used for soldering, then the solder powders form high melting point compounds to suppress remelting, but the flux volatilizes during melting causing cavities and voids in the solder joint
Solution Approach 1:
The invention extracts and removes the flux component from the soldering system, replacing it with a flux-free TLP solder paste formulation. This eliminates the source of volatilization that causes cavities and voids, while maintaining the core TLP mechanism of forming high melting point compounds between Cu and Sn powders for remelting suppression.
Solution Approach 2:
The invention creates a composite solder paste material consisting of Cu powder, Sn powder, and organic vehicle without flux. The composite structure allows the metal powders to directly form intermetallic compounds during heating, achieving reliable bonding without the harmful effects of flux decomposition.
2Object-generated harmful factors
If heating temperature is increased to improve fluidity for cavity release, then cavities can be released more easily, but thermal damage occurs to the semiconductor element
Solution Approach 1:
The invention changes the chemical composition parameters of the solder paste by eliminating flux and optimizing the Cu/Sn powder ratio and particle size distribution. This allows the soldering process to proceed at lower temperatures with sufficient fluidity, releasing cavities without subjecting the semiconductor element to damaging high temperatures.
3Object-generated harmful factors
If highly active reducing agent is added to flux to reduce oxide film, then oxide film is reduced, but reducing gas is incorporated during melting creating porous solder joint with lowered bonding strength
Solution Approach 1:
The invention removes the reducing agent component entirely by adopting a flux-free formulation. Oxide film management is achieved through alternative means such as controlled atmosphere soldering or surface preparation, eliminating the problem of reducing gas incorporation that creates porous structures and weakens bonding.
Solution Approach 2:
The invention introduces an organic vehicle as an intermediary medium that wets the metal powders and facilitates uniform distribution without requiring reducing agents. The organic vehicle decomposes cleanly without generating harmful gases that would be incorporated into the solder joint.
4Stability of the object's composition
If particle size of solder powder is reduced for uniform dispersion in flux, then uniform dispersion is achieved, but specific surface area increases making oxidation easier and voids more significant
Solution Approach 1:
The invention formulates a composite powder mixture with optimized particle size distribution where finer particles provide uniform dispersion while coarser particles reduce total surface area. The absence of flux prevents oxidation of the increased surface area, and the organic vehicle in the flux-free formulation provides protective coverage during processing.
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 approach effectively reduces void occurrence and increases shear strength in solder joints, particularly under high temperature conditions, by forming intermetallic compounds that suppress porous structures and improve heat resistance.
Implementation Method 1
a second metal formed of an alloy containing Ni and Fe... forming intermetallic compounds that suppress porous structures
Implementation Method 2
a rolling process of rolling the metal powder mixture and fabricating a preform solder
Data Source
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).