Solder Alloy Composition for Missing-Free, Durable Solder Joints
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Solution Overview
Problem
Conventional solder alloys face challenges in preventing 'missing' during soldering, especially in miniaturized electronic components, while maintaining excellent wet spreading, inhibiting intermetallic compound growth, and optimizing fracture modes under varying temperature conditions.
Innovation Solution
A solder alloy composition with specific ranges of Ag, Cu, Ni, Sb, Bi, Co, and Ge, along with optional elements, is formulated to prevent 'missing', ensure excellent wetting, inhibit intermetallic compound growth, and optimize fracture modes by modifying the surface structure to a dense configuration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional Sn-3Ag-0.5Cu solder alloy is used, then the solder joint can be formed, but breakage occurs at the joint portion under large temperature difference
Solution Approach 1:
The invention changes the compositional parameters of the solder alloy by precisely controlling the content ranges of Ag (3.0-4.0 mass%), Cu (0.5-0.8 mass%), Ni (0.01-0.2 mass%), Sb (2.0-5.5 mass%), Bi (1.5-5.5 mass%), Co (0.001-0.1 mass%), and Ge (0.001-0.1 mass%), along with satisfying specific relational expressions. These parameter changes optimize the balance between joint strength and reliability, preventing breakage under temperature cycling while maintaining adequate bonding strength.
Solution Approach 2:
The invention creates a composite solder alloy system combining multiple elements (Sn, Ag, Cu, Ni, Sb, Bi, Co, Ge) that work synergistically. The specific composition ratios and relationships create a composite material structure that simultaneously achieves high joint strength and excellent reliability under thermal stress, resolving the contradiction between these two properties.
2Reliability
If solder alloy composition is optimized for preventing missing, then wet spreading may be compromised
Solution Approach 1:
The invention optimizes the compositional parameters within specific ranges: Ag (3.0-4.0 mass%) for wettability, Bi (1.5-5.5 mass%) and Ge (0.001-0.1 mass%) for preventing missing, along with satisfying relational expressions. This balanced parameter optimization ensures both excellent wet spreading and prevention of missing defects.
Solution Approach 2:
The invention applies different functional elements to different aspects of soldering performance: Ag and Cu content optimization for wet spreading, while Bi and Ge content optimization for preventing missing. This local quality approach allows each element to specialize in specific functions, achieving both goals simultaneously.
3Reliability
If intermetallic compound growth is inhibited, then fracture mode may be adversely affected
Solution Approach 1:
The invention precisely controls the content of elements affecting intermetallic compound formation: Ni (0.01-0.2 mass%) and Co (0.001-0.1 mass%) to inhibit excessive IMC growth, while maintaining Ag (3.0-4.0 mass%) and Cu (0.5-0.8 mass%) for adequate strength. The relational expressions further refine this balance to achieve both joint durability and appropriate fracture mode.
Solution Approach 2:
The invention optimizes the compositional parameters within specific ranges: Ag (3.0-4.0 mass%) for wettability, Bi (1.5-5.5 mass%) and Ge (0.001-0.1 mass%) for preventing missing, along with satisfying relational expressions. This balanced parameter optimization ensures both excellent wet spreading and prevention of missing defects.
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 composition effectively prevents 'missing', ensures excellent wetting and spreadability, inhibits intermetallic compound growth, and optimizes fracture modes, enhancing the reliability and durability of solder joints in harsh environments.
Implementation Method 1
modifying the surface structure to a dense configuration
Implementation Method 2
ensures excellent wetting and spreadability
Implementation Method 3
inhibiting intermetallic compound growth
Data Source
AI summary
A solder alloy has an alloy composition consisting of, in mass %, Ag: from 3.2 to 3.8%, Cu: from 0.6 to 0.8%, Ni: from 0.01 to 0.2%, Sb: from 2 to 5.5%, Bi: from 1.5 to 5.5%, Co: from 0.001 to 0.1%, Ge: from 0.001 to 0.1%, and optionally at least one of Mg, Ti, Cr, Mn, Fe, Ga, Zr, Nb, Pd, Pt, Au, La and Ce: 0.1% or less in total, with the balance being Sn. The alloy composition satisfies the following relationship (1): 2.93≤{(Ge/Sn)+(Bi/Ge)}×(Bi/Sn) (1). In the relationship (1), each of Sn, Ge, and Bi represents the content (mass %) in the alloy composition.