Sn-Ag-Bi-In-Cu Solder Composition for Thermal Fatigue
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Solution Overview
Problem
Solder materials with a Sn—Ag—Bi—In composition do not consistently exhibit high thermal fatigue properties when used for bonding Au substrate electrodes, leading to reduced reliability in electronic circuit board soldering due to In content variations and interactions with Ni plating containing P, which affects the Au and Cu electrodes differently.
Innovation Solution
A solder material composition of Sn—Ag—Bi—In—Cu is developed, where Ag ranges from 0.3 to 4.0 mass %, Bi from 0 to 1.0 mass %, and Cu from 0 to 1.2 mass %, with In content optimized between 5.2 and 6.8 mass % based on Cu content, ensuring a balance of at least 87 mass % Sn, to maintain thermal fatigue properties and prevent In content reduction during soldering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If In content is increased to improve thermal fatigue properties, then thermal fatigue resistance improves, but In content varies during soldering due to interactions with Ni plating containing P
Solution Approach 1:
The patent specifies precise parameter ranges for In (5.2-6.8 mass%), Cu (0-1.2 mass%), and other elements to control the chemical interactions during soldering. By optimizing these compositional parameters, the patent achieves thermal fatigue resistance while preventing excessive In consumption through reactions with Ni plating containing P.
Solution Approach 2:
The patent uses a multi-element composite solder material composition (Sn-Ag-Bi-In-Cu) where each element serves a specific function. The Cu element specifically addresses the interaction with Ni plating containing P, while In provides thermal fatigue resistance, and Ag/Bi contribute to melting point and wettability. This composite approach resolves the contradiction by distributing functions across multiple elements.
2Stability of the object's composition
If Cu content is increased to suppress In content reduction, then In content stability improves, but the composition complexity increases
Solution Approach 1:
The patent optimizes the Cu content parameter within a specific range (0-1.2 mass%) to achieve the desired effect of suppressing In content reduction during soldering. This controlled parameter change allows the patent to address composition stability without excessive complexity, as Cu serves multiple functions including suppressing In consumption and contributing to intermetallic compound formation.
3Strength
If Ag content is optimized to improve wettability, then bonding strength improves, but the cost of solder material increases
Solution Approach 1:
The patent specifies an optimized Ag content range (0.3-4.0 mass%) that balances wettability improvement with cost control. This parameter optimization ensures sufficient bonding strength through enhanced wettability while avoiding excessive Ag content that would unnecessarily increase material cost. The lower limit of 0.3 mass% provides minimal wettability benefit, while the upper limit of 4.0 mass% prevents excessive cost increase.
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 optimized solder material achieves reliable thermal fatigue properties and maintains In content within the required range, ensuring bonding integrity across Au and Cu electrodes, meeting or exceeding 2000 cycles in heat cycle tests and supporting the use in various electronic components.
Implementation Method 1
thermal fatigue properties with respect to fatigue fracture occurring due to thermal stress accompanied by a temperature change are enhanced by a technique using an effect of solid solution. The solid solution denotes a technique of preventing deterioration of solder material by replacing a part of metal atoms arranged in a lattice with a different metal atom so as to distort such a lattice.
Data Source
AI summary
Solder material used in soldering of an Au electrode including Ni plating containing P includes Ag satisfying 0.3≦[Ag]≦4.0, Bi satisfying 0≦[Bi]≦1.0, and Cu satisfying 0<[Cu]≦1.2, where contents (mass %) of Ag, Bi, Cu and In in the solder material are denoted by [Ag], [Bi], [Cu], and [In], respectively. The solder material includes In in a range of 6.0≦[In]≦6.8 when [Cu] falls within a range of 0<[Cu]<0.5, In in a range of 5.2+(6−(1.55×[Cu]+4.428))≦[In]≦6.8 when [Cu] falls within a range of 0.5≦[Cu]≦1.0, In in a range of 5.2≦[In]≦6.8 when [Cu] falls within a range of 1.0<[Cu]≦1.2. A balance includes only not less than 87 mass % of Sn.