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, and suffer from intermetallic compound growth and unfavorable fracture modes under temperature variations, which affect the reliability of solder joints in harsh automotive environments.
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 inhibit intermetallic compound growth and optimize fracture modes, ensuring excellent wetting and spreading while preventing 'missing' phenomena.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional Sn-Ag-Cu solder alloy is used, then the solder joint can be formed, but breakage occurs at the joint portion under temperature difference
Solution Approach 1:
The invention changes the chemical composition parameters of the solder alloy by adding specific elements (Ni: 0.01-0.2 mass%, Co: 0.001-0.1 mass%, Ge: 0.001-0.1 mass%) and controlling the ratios of existing elements (Ag: 3.2-3.8 mass%, Cu: 0.6-0.8 mass%, Sb: 2.0-5.5 mass%, Bi: 1.5-5.5 mass%). This compositional parameter optimization prevents joint breakage under temperature differences while maintaining solderability and connection strength.
Solution Approach 2:
The invention creates a composite solder alloy system by combining multiple elements (Sn, Ag, Cu, Ni, Sb, Bi, Co, Ge) that work synergistically. The composite structure forms specific intermetallic compounds and phases that improve both the mechanical strength and thermal shock resistance of the solder joint, preventing breakage under temperature cycling conditions.
2Strength
If solder alloy composition is optimized for strength, then fracture resistance improves, but wetting and spreading properties deteriorate
Solution Approach 1:
The invention optimizes the compositional parameters within specific ranges to achieve the balance between strength and wettability. The controlled addition of Ni (0.01-0.2 mass%), Co (0.001-0.1 mass%), and Ge (0.001-0.1 mass%) along with optimized Ag (3.2-3.8 mass%) and Cu (0.6-0.8 mass%) content creates a composition that provides both adequate mechanical strength and good wetting properties without excessive intermetallic compound formation.
3Reliability
If Ag content is increased to prevent cracking, then mechanical strength improves, but cost and complexity increase
Solution Approach 1:
The invention sets the Ag content within a specific range (3.2-3.8 mass%) and combines it with controlled amounts of other elements (Cu: 0.6-0.8 mass%, Ni: 0.01-0.2 mass%, Co: 0.001-0.1 mass%, Ge: 0.001-0.1 mass%). This balanced compositional approach achieves crack prevention in temperature difference environments without requiring excessive Ag content, thereby controlling cost and compositional complexity while maintaining reliability.
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 alloy composition effectively prevents 'missing', inhibits intermetallic compound growth, and optimizes fracture modes, enhancing the reliability and durability of solder joints in extreme temperature environments.
Implementation Method 1
the growth of an intermetallic compound after soldering is inhibited
Implementation Method 2
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%
Implementation Method 3
excellent wet spreading is exhibited
Data Source
Figure 1
Figure 2
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 In the relationship (1), each of Sn, Ge, and Bi represents the content (mass%) in the alloy composition.