Intermetallic Compound Solder Paste for High-Temperature Bonding
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conductive materials used in electronic component mounting, such as solder pastes, face challenges with low-melting point metals like Sn remaining after soldering, leading to reduced bonding strength and reliability, especially under high temperatures, due to slow diffusion rates and the need for prolonged high-temperature heating which is impractical for productivity.
Innovation Solution
A conductive material comprising a first metal (Sn or its alloy with 70% or more Sn) and a second metal that forms an intermetallic compound with a melting point of 310°C or higher, having a lattice constant difference of 50% or greater, which facilitates rapid diffusion and complete conversion into a high-melting point compound, reducing low-melting point components and enhancing high-temperature bonding strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional solder paste with low-melting point metal (Sn) is used, then bonding is established at low temperature, but Sn remains after soldering due to slow diffusion rate, causing reduced bonding strength and reliability under high temperature
Solution Approach 1:
The invention changes the material parameters by replacing pure Sn with intermetallic compounds having specific melting points and compositions. The solder paste uses metal balls consisting of intermetallic compounds (e.g., Cu6Sn5, Cu3Sn) instead of conventional Sn-based alloys, fundamentally altering the physical and chemical parameters to achieve complete reaction without residual low-melting point metal.
Solution Approach 2:
The invention employs composite material structure by combining multiple intermetallic compounds in specific ratios. The solder paste contains a mixture of different intermetallic compound balls (e.g., Cu6Sn5 and Cu3Sn in controlled proportions) that work synergistically to provide both low-temperature bonding capability and high-temperature stability, eliminating the need for residual Sn while maintaining reliability.
2Reliability
If heating at high temperature for long time is applied to fully convert Sn into intermetallic compound, then bonding strength increases, but productivity decreases due to impractical processing time
Solution Approach 1:
The invention applies preliminary action by pre-forming intermetallic compound balls before the soldering process. Instead of starting with Sn that needs to diffuse during soldering, the material is pre-prepared in the desired intermetallic compound form, so that during soldering only melting and bonding occur, not slow diffusion reactions. This dramatically reduces the required heating time while maintaining strong bonds.
Solution Approach 2:
The invention changes the thermal parameters by selecting intermetallic compounds with appropriate melting points that enable rapid bonding. The chosen intermetallic compounds melt at temperatures that allow complete reaction and bonding within standard soldering timeframes (seconds to minutes), eliminating the need for prolonged high-temperature treatment while achieving full conversion and strong bonding.
3Ease of operation
If Sn remains in solder paste after soldering, then low-temperature bonding is achieved, but Sn melts and runs off during subsequent reflow soldering, causing low reliability
Solution Approach 1:
The invention changes the melting point parameter by replacing Sn (melting point 232°C) with intermetallic compounds having higher melting points (Cu6Sn5: 484°C, Cu3Sn: 227°C but forms stable structure). This parameter change ensures the bonding material remains stable during reflow soldering temperatures (typically 200-250°C) while still enabling low-temperature bonding through controlled melting and reaction of the intermetallic compounds.
Solution Approach 2:
The invention uses composite intermetallic compound materials that combine the benefits of different compounds. By formulating solder paste with specific ratios of intermetallic compounds, the material achieves both low-temperature bonding capability (through selective melting) and high-temperature stability (through the presence of higher-melting-point compounds that prevent runaway melting and maintain structural integrity during reflow).
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 high-temperature bonding with increased strength and reliability, preventing remelting issues during reflow soldering, thus ensuring robust semiconductor device mounting with minimal residual low-melting point components.
Implementation Method 1
a combination of Cu (high-melting point metal) and Sn (low-melting point metal) has a low diffusion rate, so that Sn, a low-melting point metal, remains
Implementation Method 2
solder paste containing low-melting point metal (e.g. Sn) balls 51, high-melting point metal (e.g. Cu) balls 52 and a flux 53 as schematically shown in FIG. 4(a) is heated and thereby reacted
Data Source
AI summary
A conductive material that includes a metal component consisting of a first metal and a second metal having a melting point higher than that of the first metal, wherein the first metal is Sn or an alloy containing 70% by weight or more of Sn, and the second metal is a metal or alloy which forms an intermetallic compound having a melting point of 310° C. or higher with the first metal and has a lattice constant difference of 50% or greater between itself and the intermetallic compound generated at the circumference of the second metal.