Copper-Added Tin Solder Paste for Preventing Copper Wire Dissolution
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing reflow soldering methods result in excessive dissolution of copper wires into the solder, leading to reduced mechanical strength and electrical conductance due to the formation of Kirkendall voids and volume shrinkage during the formation of Cu3Sn IMC layers, which can cause wire breakage and deterioration of the solder joint.
Innovation Solution
A copper-added tin-based solder paste is used, containing a mixture of tin alloy powder and copper powder, with a copper powder ratio of 0.2% to 20%, to form intermetallic compounds that inhibit copper dissolution and maintain wire diameter, using a reflow soldering process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If reflow soldering is performed using conventional solder paste, then solder joint is formed to connect copper wire to electrode terminal, but copper wire dissolves excessively into the solder base leading to wire thinning and strength reduction
Solution Approach 1:
Copper powder particles are added to the solder paste before reflow soldering to preemptively counteract the dissolution of copper wire into the solder base. The pre-added copper particles serve as a copper source that satisfies the copper diffusion demand, thereby preventing excessive copper wire dissolution and maintaining wire diameter and strength.
Solution Approach 2:
The composition of the solder paste is modified by adding copper powder particles with specific size range (1-50 μm) and controlled content (0.1-35 wt%). This parameter change alters the copper concentration profile during soldering, reducing the concentration gradient that drives copper diffusion from the wire into the solder base.
2Reliability
If Cu3Sn intermetallic compound layer forms during soldering, then electrical connection is established, but volume shrinkage occurs creating Kirkendall voids that reduce mechanical strength
Solution Approach 1:
Copper powder particles are incorporated into the solder paste in advance to provide a reservoir of copper atoms. During the formation of Cu3Sn intermetallic compound layer, these pre-positioned copper particles dissolve to supply copper atoms, compensating for the volume shrinkage and preventing Kirkendall void formation, thereby maintaining mechanical strength.
Solution Approach 2:
The solder paste is formulated as a composite material containing tin alloy powder, flux, and copper powder particles. This composite structure enables simultaneous achievement of electrical conduction through Cu3Sn layer formation and mechanical strength maintenance through in-situ copper supplementation from the embedded copper particles.
3Productivity
If multiple reflow soldering cycles are performed, then assembly is completed, but copper wire diameter continuously decreases leading to wire breakage risk
Solution Approach 1:
Copper powder particles are pre-added to the solder paste to create a copper reservoir that can sustain multiple reflow cycles. The particles dissolve progressively across cycles, providing continuous copper supplementation that prevents wire diameter reduction and enables repeated soldering operations without wire degradation.
Solution Approach 2:
The copper powder particles in the solder paste provide continuous copper supplementation across multiple reflow soldering cycles. This continuous action maintains the copper concentration gradient, preventing excessive copper diffusion from the wire and preserving wire diameter throughout the multi-cycle assembly process.
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 copper-added solder paste effectively prevents copper wire thinning and maintains mechanical strength and electrical conductance by forming intermetallic compounds that suppress copper diffusion and phase transformation, ensuring the wire retains approximately 85-90% of its original diameter after multiple reflow cycles.
Implementation Method 1
copper powder particles enveloped in an intermetallic compound are distributed within the soldering member
Implementation Method 2
the copper particles of the copper wire continuously dissolve and diffuse into the tin base
Implementation Method 3
the connection interface is gradually heated under a controlled temperature profile to melt the solder in the solder paste
Data Source
AI summary
A tin-based solder paste, a soldering method and an electronic component formed thereby are provided. A copper powder is mixed into the tin-based solder paste, and a weight ratio of the copper powder to an overall metallic powder ranges within 0.2-20%. The electronic component includes a core element, a copper wire and a soldering member. The core element has thereon an electrode terminal. One end of the copper wire is in contact with the electrode terminal. The soldering member covers the one end of the copper wire and the electrode terminal to form the solder joint electrically connecting the copper wire to the electrode terminal, wherein copper-based particles enveloped in an intermetallic compound are dispersed in the soldering member, and the copper-based particles have a particle size of 1-50 μm.