Lead-Free Solder Alloy Composition to Suppress Ni Leaching and Voids
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Solution Overview
Problem
Existing solder alloys face challenges in achieving high tensile strength, suppressing Ni leaching, and preventing void generation at bonded interfaces, particularly in high-integration semiconductor packages like QFP and BGA, while also being lead-free and antimony-free.
Innovation Solution
A solder alloy composition comprising Ag: 1.0 to 4.0%, Cu: 0.1 to 1.0%, Ni: 0.005 to 0.3%, Co: 0.003 to 0.1%, and Ge: 0.001 to 0.015% with a balanced ratio satisfying (Ni/Co) × (1/Ag) × Ge < 0.05, which enhances tensile strength, suppresses Ni leaching, and prevents void formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If Sn-Ag-Cu solder alloy is used to improve wettability and adhesive strength, then bonding performance is improved, but Ni leaching increases and void generation occurs at the bonded interface
Solution Approach 1:
The patent modifies the chemical composition parameters of the solder alloy by adding specific amounts of Co (0.003-0.1 mass%) and Ge (0.001-0.015 mass%) elements to the Sn-Ag-Cu base alloy. This parameter change alters the alloy's interaction with the Ni layer, suppressing Ni leaching while maintaining adhesive strength through optimized compositional ratios.
Solution Approach 2:
The patent creates a composite solder alloy system by combining multiple elements (Sn, Ag, Cu, Co, Ge) with specific compositional relationships. The synergistic interaction between these elements forms a composite material that simultaneously achieves high adhesive strength and Ni leaching suppression, with the Co and Ge elements working together to control the metallurgical reactions at the bonded interface.
2Strength
If Ni layer is retained on back metal to suppress Ni diffusion, then adhesive strength is maintained, but Ni leaching into molten solder occurs and voids increase at the interface
Solution Approach 1:
The patent changes the chemical composition parameters of the solder alloy to include Co and Ge elements in specific ratios. This parameter modification alters the thermodynamic and kinetic conditions at the bonded interface, enabling the Ni layer to be retained without excessive leaching or void formation by controlling the dissolution and diffusion processes through compositional optimization.
Solution Approach 2:
The patent creates different local chemical environments at the bonded interface by introducing Co and Ge elements. These elements locally modify the interaction between the solder alloy and the Ni layer, suppressing Ni leaching in specific regions while maintaining wettability and adhesive strength, thereby improving the local quality of the bonded interface.
3Stability of the object's composition
If solder alloy composition is optimized for heat cycle resistance, then thermal stability is improved, but tensile strength and impact resistance may be compromised
Solution Approach 1:
The patent optimizes multiple compositional parameters simultaneously by adding Co and Ge elements in specific amounts to the Sn-Ag-Cu alloy. This multi-parameter optimization achieves a balanced composition that provides both heat cycle resistance through improved thermal stability and high tensile strength through enhanced microstructure formation, resolving the trade-off between thermal and mechanical properties.
Solution Approach 2:
The patent develops a composite solder alloy system where Co and Ge elements work synergistically with Sn, Ag, and Cu to simultaneously improve thermal stability and mechanical strength. The composite material structure formed by this multi-element combination provides both heat cycle resistance and high tensile strength, eliminating the need to compromise one property for the other.
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 alloy achieves high tensile strength, effectively inhibits Ni leaching, and discharges voids at the bonded interface, suitable for both BGA and QFP applications, ensuring reliable electronic connections.
Implementation Method 1
a barrier layer such as Ti is usually formed on the back metal to suppress Ni from diffusing into the silicon chip
Implementation Method 2
the molten solder wets the microelectrode, so that solder bumps are formed on the microelectrodes
Data Source
AI summary
Provided are a solder alloy and a solder joint which have high tensile strength, can suppress Ni leaching and can suppress generation of voids at a bonded interface. The solder alloy has an alloy composition consisting of, by mass %, —Ag: 1.0 to 4.0%, Cu: 0.1 to 1.0%, Ni: 0.005 to 0.3%, Co: 0.003 to 0.1%, and Ge: 0.001 to 0.015% with the balance being SnThe alloy composition satisfies the following relation (1):0.00030<(Ni/Co)×(1/Ag)×Ge<0.05 (1)Co, Ag, and Ge in the relation (1) each represent the contents (mass %) in the alloy composition.