Molded Solder Composition for High-Temperature SiC Bonding
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Solution Overview
Problem
Conventional solder alloys used for bonding power semiconductors like SiC elements have a solidus temperature lower than 300°C, making them unsuitable for high-temperature applications and hindering productivity due to the need for prolonged high-temperature heating and pressing, which can lead to erosion and void formation.
Innovation Solution
A molded solder composed of a mixture of metal powders with different solidus and liquidus temperatures, where the first metal powder with a lower liquidus temperature is melted and the second with a higher liquidus temperature is dispersed, forming an intermetallic compound that increases the solidus temperature of the solder, allowing bonding at temperatures as low as 250°C without preheating, thus preventing remelting and improving thermal conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional solder alloy with solidus temperature lower than 300°C is used, then bonding process is simpler, but it cannot bond SiC elements reliably at high temperatures and causes remelting during operation
Solution Approach 1:
The patent uses a composite material consisting of high melting point metal particles (such as Ag, Cu, or Mo with melting points above 300°C) dispersed in a solder alloy matrix. This composite structure allows the bonding material to maintain its shape and strength at high temperatures while still providing good bonding properties. The high melting point particles act as reinforcement that prevents remelting during SiC element operation, directly resolving the contradiction between bonding reliability and solidus temperature.
Solution Approach 2:
The patent changes the physical and chemical parameters of the bonding material by incorporating high melting point metal particles with specific melting points above 300°C. This parameter change transforms the bonding material from a conventional low-temperature solder alloy to a high-temperature resistant composite, enabling reliable bonding of SiC elements that operate at elevated temperatures without remelting.
2Strength
If metal powder is sintered at high temperature (200°C to 300°C) to bond SiC elements, then bonding strength is improved, but productivity decreases due to prolonged heating and pressing time
Solution Approach 1:
The patent utilizes phase transition by melting the solder alloy matrix at a relatively low temperature while maintaining the high melting point metal particles in solid state. This selective phase transition allows the bonding material to become fluid for filling and wetting, then solidify to provide strong bonding, eliminating the need for prolonged high-temperature sintering and significantly improving productivity while maintaining bonding strength.
Solution Approach 2:
The solder alloy matrix acts as an intermediary that facilitates bonding at lower temperatures. It provides a eutectic reaction mechanism that enables the high melting point metal particles to be embedded and bonded without requiring the entire system to reach high sintering temperatures, thus reducing heating and pressing time while maintaining bonding strength.
3Reliability
If high melting point metal particles are added to increase solidus temperature, then remelting is prevented, but manufacturing complexity increases
Solution Approach 1:
The patent applies local quality by concentrating the high melting point metal particles specifically at the bonding interface where they are most needed for preventing remelting during SiC element operation. The solder alloy matrix provides the bulk bonding properties, while the dispersed high melting point particles provide localized high-temperature resistance exactly where required, optimizing reliability without excessive complexity.
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 enables reliable bonding of SiC elements to a DCB substrate at 250°C, preventing remelting and void formation, while maintaining high thermal conductivity and productivity by adjusting the melting temperature through intermetallic compound formation, resulting in a highly reliable solder joint.
Implementation Method 1
the first metal powder has a first solidus temperature and a first liquidus temperature... when the molded solder is heated to a temperature equal to or higher than the first liquidus temperature, the first metal powder is melted
Implementation Method 2
the second metal powder... is dispersed, forming an intermetallic compound that increases the solidus temperature of the solder
Implementation Method 3
maintaining high thermal conductivity... resulting in a highly reliable solder joint
Data Source
AI summary
Molded solder includes first metal powder and second metal powder. The first metal powder has a first solidus temperature and a first liquidus temperature and includes an alloy containing metal elements. The second metal powder has a melting temperature or a second solidus temperature and a second liquidus temperature and includes single metal element or an alloy containing metal elements. The melting temperature and the second liquidus temperature are higher than the first liquidus temperature. The molded solder is so constructed that a mixture of the first metal powder and the second metal powder are press-molded. The molded solder is so constructed that a first solidus temperature of a solder becomes higher when the molded solder becomes the solder after the first metal powder has been melted by heating the molded solder at a temperature equal to or higher than the first liquidus temperature.