Sn-Cu-Ni Solder Joint Composition for Crack Resistance
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Solution Overview
Problem
Solder joints formed with Pb-free solder alloys, such as Sn-Cu and Sn-Cu-Ni, are prone to cracks and fractures, leading to reduced joint strength and increased electrical resistance, which can cause heating and fire hazards due to the stress and thermal distortions during the solidification process.
Innovation Solution
A lead-free solder alloy composition of 0.01-7.6% Cu, 0.001-6% Ni, with the remaining part being Sn, forming intermetallic compounds like (Cu,Ni)6Sn5 with a hexagonal crystalline structure, and optionally replacing Ni with Co, Mn, Zn, or Pt, to stabilize the crystalline structure and prevent crack formation during solidification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Pb-free solder alloys (Sn-Cu, Sn-Cu-Ni) are used, then environmental safety and material availability are improved, but crack generation and joint reliability deteriorate
Solution Approach 1:
The patent applies parameter changes by precisely controlling the compositional parameters of the solder alloy. Specifically, it limits Cu content to 0.01-7.6 wt% and Ni content to 0.001-6 wt%, with optimal ranges of 0.03-0.1 wt% for Cu and 0.003-0.03 wt% for Ni. This compositional parameter optimization prevents excessive intermetallic compound formation while maintaining crack resistance and joint reliability.
Solution Approach 2:
The patent creates a composite material system by combining Sn-Cu-Ni alloy with a specifically controlled intermetallic compound layer. The intermetallic compound layer, formed by the Cu-Ni-Sn system, acts as a protective composite structure that prevents crack propagation. This composite approach integrates the base solder alloy with a functional intermetallic layer to achieve superior crack resistance.
2Stability of the object's composition
If Cu and Ni are added to Sn-based solder alloy, then intermetallic compound formation is controlled, but composition complexity increases
Solution Approach 1:
The patent manages composition complexity through systematic parameter changes and constraints. It establishes specific compositional ranges: Cu at 0.01-7.6 wt% and Ni at 0.001-6 wt%, with preferred ranges of 0.03-0.1 wt% Cu and 0.003-0.03 wt% Ni. These parameter specifications balance intermetallic compound stability with compositional simplicity, avoiding excessive element additions while achieving the desired stable (Cu,Ni)6Sn5 phase formation.
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 proposed solder joint composition significantly reduces crack generation and stress preservation, resulting in a highly reliable solder joint that is resistant to cracking and thermal distortions, maintaining strength and stability over time.
Implementation Method 1
the intermetallic compound, when solidified, has a hexagonal crystalline structure
Data Source
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AI summary
A solder joint manufactured of an alloy essentially composed of 0.01-7.6 wt% Cu, 0.001-6 wt% Ni, and the remaining of Sn. Each of Cu and Ni has a maximum concentration range. The lower limit of the range of Ni is 0.01 wt% and preferably 0.03 wt%. The upper limit of the range of Ni is 0.3 wt% and preferably 0.1 wt%. The lower limit of the range of Cu is 0.1 wt% and preferably 0.2 wt%. The upper limit of the range of Cu is 7 wt% and preferably 0.92 wt%. The invention includes the solder joint essentially having these compositions.