Silver-Bismuth Paste Bonding for High-Temperature Semiconductor Devices
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Solution Overview
Problem
Current bonding methods for semiconductor devices, such as silicon carbide (SiC) devices, face challenges with high-temperature operation due to solder materials with low melting points and the use of expensive high-temperature solders or sintering processes that require long times and can increase electrical resistance with non-metallic mediator materials like glass frit.
Innovation Solution
A method using a silver paste containing silver and bismuth particles, where the paste is heated above the melting point of bismuth to form a bonding layer, allowing for transient liquid phase diffusion bonding without the need for glass frit, thereby reducing sintering time and electrical resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If solder material is used for bonding semiconductor devices, then bonding process is simple, but bonding temperature is limited to below 230°C
Solution Approach 1:
The invention changes the material composition parameters of the bonding paste by incorporating bismuth particles (1-10 μm) alongside silver particles. This compositional parameter change enables the bonding process to occur at temperatures above 230°C (specifically 250-300°C) while maintaining reliable high-temperature operation stability, resolving the contradiction between bonding temperature and operational reliability.
2Temperature
If high-temperature solder containing gold is used to increase bonding temperature, then high-temperature operation is enabled, but cost increases and joining strength deteriorates
Solution Approach 1:
The invention replaces expensive gold-containing high-temperature solder with a cost-effective formulation using silver particles (1-10 μm) and bismuth particles. This substitution achieves the same high-temperature bonding capability (250-300°C) without the high manufacturing cost of gold, resolving the contradiction between bonding temperature and manufacturing cost.
3Temperature
If sintering process is used for high-temperature bonding with silver particles, then high-temperature operation is enabled, but process time increases and device characteristics deteriorate
Solution Approach 1:
The invention utilizes the phase transition of bismuth from solid to liquid at its melting point (271°C) to enable rapid bonding. When heated to 250-300°C, the bismuth particles melt and facilitate immediate bonding between silver particles and substrates, eliminating the need for prolonged sintering processes. This phase transition mechanism resolves the contradiction between achieving high-temperature bonding and minimizing process time.
4Productivity
If glass frit is added to activate sintering between large-sized silver particles, then sintering is activated, but residual glass increases electrical resistance
Solution Approach 1:
The invention extracts and eliminates the glass frit component from the bonding paste formulation while retaining the essential bonding function through the silver-bismuth particle system. By removing the non-conductive glass frit, the invention achieves efficient sintering activation through bismuth's phase transition without introducing residual glass that would increase electrical resistance, thus resolving the contradiction between sintering efficiency and electrical resistance.
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
This method enables high-temperature bonding of semiconductor devices with reduced exposure time and lower electrical resistance, using relatively large-sized silver particles and eliminating the need for non-metallic sintering mediator materials.
Implementation Method 1
heating the silver paste to transform the bismuth particles into bismuth liquids
Implementation Method 2
diffusing the bismuth liquids into the silver particles; and diffusing the silver particles into the bismuth liquids
Data Source
AI summary
A method for bonding with a silver paste includes coating a semiconductor device or a substrate with the silver paste. The silver paste contains a plurality of silver particles and a plurality of bismuth particles. The method further includes disposing the semiconductor on the substrate and forming a bonding layer by heating the silver paste, wherein the semiconductor and the substrate are bonded to each other by the bonding layer.