Sn Alloy Joining with Cu-Ni Insert for High-Temperature Reliability
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Solution Overview
Problem
Existing soldering methods using solder pastes with high melting point metals and Sn result in low joint strength at elevated temperatures due to residual Sn, which can melt and flow during reflow soldering, leading to unreliable bonds and air gaps in electronic joints.
Innovation Solution
A joining method using an insert material with a second metal alloy, such as Cu—Ni or Cu—Mn, to form an intermetallic compound with Sn, reducing Sn content and enhancing high-temperature joint reliability by rapid diffusion and heat treatment, ensuring no air gaps and improved heat resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If solder paste containing Sn and high melting point metal is used for mounting, then the electronic part can be mounted on the substrate, but residual Sn remains after soldering which deteriorates joint strength at elevated temperatures
Solution Approach 1:
The invention extracts the harmful residual Sn from the joint structure by introducing a third metal element that selectively reacts with and removes Sn. The third metal forms intermetallic compounds with Sn, effectively extracting the problematic residual Sn from the joint and converting it into a controlled intermetallic layer that does not compromise high-temperature performance.
Solution Approach 2:
The third metal acts as an intermediary substance between the Sn-containing solder paste and the high melting point metal. It mediates the interaction by forming intermediate intermetallic compounds that prevent direct harmful effects of residual Sn while maintaining the bonding function. This intermediary layer controls the diffusion and reaction processes to achieve reliable joints.
2Reliability
If heating is extended to convert all Sn to intermetallic compound, then Sn residue is eliminated, but productivity is reduced due to impractical heating time
Solution Approach 1:
The invention changes the chemical parameters of the solder paste by adding a third metal element with specific reactivity characteristics. This parameter change enables selective reaction kinetics where the third metal preferentially reacts with Sn at lower temperatures and shorter times, eliminating the need for prolonged heating while still achieving complete Sn conversion to intermetallic compounds.
Solution Approach 2:
The third metal creates local quality differences in the solder paste composition, with specific regions having enhanced reactivity toward Sn. This localized chemical property allows the reaction to proceed efficiently at the interface between the solder paste and the third metal, enabling complete Sn consumption without requiring extended heating of the entire assembly.
3Reliability
If conventional solder paste is used, then mounting process is simple, but Sn may melt and flow out during reflow soldering causing reliability problems
Solution Approach 1:
The invention creates a composite solder paste material containing Sn, high melting point metal, and a third metal element. This composite structure combines the beneficial properties of each component: Sn provides solderability, the high melting point metal provides thermal stability, and the third metal provides Sn scavenging capability. The composite material prevents Sn flow during reflow while maintaining ease of use.
4Reliability
If solder paste with high melting point metal and Sn is used, then joining can be performed, but air gaps are formed in the joint structure reducing reliability
Solution Approach 1:
The third metal serves as an intermediary that fills and seals potential void spaces during the soldering process. It forms intermetallic compounds that create a dense, gap-free joint structure by reacting with Sn and occupying spaces that would otherwise remain as air gaps. This intermediary action ensures complete wetting and eliminates 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 method produces a highly reliable joint with high heat resistance and strength, preventing Sn residue and air gaps, maintaining bond integrity under reflow and high-temperature conditions.
Implementation Method 1
the first joining object and the second joining object are subjected to heat treatment with the insert material located therebetween to produce an intermetallic compound of the first metal which the first joining object and/or the second joining object has, and the second metal composing the insert material
Implementation Method 2
produce an intermetallic compound of the first metal which the first joining object and/or the second joining object has, and the second metal composing the insert material
Implementation Method 3
the first joining object and the second joining object are subjected to heat treatment with the insert material located therebetween
Data Source
AI summary
A first joining object and a second joining object are joined to each other using an insert material. The first joining object and/or the second joining object has a first metal composed of Sn or an alloy containing Sn. The insert material contains, as a main component, a second metal which is an alloy containing at least one selected from among Ni, Mn, Al and Cr, and Cu, and is located between the first joining object and the second joining object. When subjected to heat treatment to produce an intermetallic compound of the first metal and the second metal, the first joining object and the second joining object are joined to each other.