Solder Alloy Composition for Heat-Conductive, Cycle-Resistant Joints
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional solder alloys face challenges in achieving both high heat cycle resistance and heat conductivity while maintaining excellent wettability, as these properties are often mutually exclusive, and existing solder alloys with high heat cycle resistance suffer from poor heat conductivity and wettability issues due to factors like supercooling and compound liberation at the joint interface.
Innovation Solution
A solder alloy composition with specific ranges of Ag, Cu, Bi, Sb, Fe, and Co is developed, which suppresses supercooling, refines crystal grains, and adjusts compound precipitation to enhance heat conductivity and wettability, ensuring the alloy performs well in extreme temperature environments without compromising heat cycle resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional solder alloys with high heat cycle resistance are used, then heat cycle resistance is improved, but heat conductivity deteriorates
Solution Approach 1:
The patent applies parameter changes by precisely controlling the compositional ratios of multiple alloying elements (Sn-3.0 to 3.8% Ag, 0.1 to 1.0% Cu, 0.01 to 0.5% Bi, 0.1 to 5.0% Sb, 0.001 to 0.05% Fe, 0.001 to 0.02% Co) to achieve optimal balance between heat cycle resistance and heat conductivity. This compositional optimization resolves the contradiction by adjusting material parameters to simultaneously satisfy both requirements.
Solution Approach 2:
The patent employs composite materials by creating a multi-element solder alloy system that combines Sn base metal with multiple additive elements (Ag, Cu, Bi, Sb, Fe, Co). Each element contributes specific properties: Ag and Cu enhance strength and heat conductivity, Bi improves heat cycle resistance, Sb refines microstructure, and Fe/Co suppress unwanted precipitates. The synergistic combination resolves the contradiction between heat cycle resistance and heat conductivity.
2Reliability
If conventional solder alloys with high heat cycle resistance are used, then heat cycle resistance is improved, but wettability deteriorates
Solution Approach 1:
The patent applies parameter changes by optimizing the Bi content to 0.01 to 0.5% and Sb content to 0.1 to 5.0%, which enhances heat cycle resistance through microstructural refinement while maintaining adequate wettability. The controlled compositional parameters prevent excessive formation of brittle intermetallic compounds that would harm wettability, thus resolving the contradiction.
Solution Approach 2:
The patent applies local quality by creating a refined microstructure with uniformly distributed fine intermetallic compounds (Cu6Sn5, Ag3Sn, SnSb) throughout the solder matrix. This local microstructural optimization ensures both high heat cycle resistance through uniform stress distribution and good wettability through appropriate surface characteristics, resolving the contradiction between these two properties.
3Temperature
If heat conductivity of solder joint is improved, then heat radiation of electronic circuits is improved, but heat cycle resistance may deteriorate
Solution Approach 1:
The patent applies parameter changes by precisely controlling Ag content (3.0 to 3.8%) and Cu content (0.1 to 1.0%) to optimize heat conductivity while maintaining heat cycle resistance. The balanced compositional parameters ensure sufficient heat conducting phases (Ag3Sn, Cu6Sn5) are present for good heat conductivity, while the overall microstructure remains refined for high heat cycle resistance, resolving the contradiction.
Solution Approach 2:
The patent employs composite materials by incorporating multiple elements with complementary functions: Ag and Cu provide heat conduction pathways, while Bi and Sb contribute to microstructural refinement and heat cycle resistance. The composite alloy system achieves synergistic effects where heat conductivity and heat cycle resistance are simultaneously optimized, resolving the contradiction between these properties.
4Temperature
If compound precipitation at joint interface is suppressed, then heat conductivity is improved, but heat cycle resistance may deteriorate
Solution Approach 1:
The patent applies parameter changes by controlling the Fe content (0.001 to 0.05%) and Co content (0.001 to 0.02%) to suppress excessive compound precipitation at the joint interface, thereby maintaining good heat conductivity. Simultaneously, the controlled Sb content (0.1 to 5.0%) ensures sufficient SnSb compound formation for heat cycle resistance, resolving the contradiction through precise compositional optimization.
Solution Approach 2:
The patent applies local quality by creating a controlled gradient in compound distribution: fine, uniformly distributed intermetallic compounds (Cu6Sn5, Ag3Sn, SnSb) throughout the solder matrix provide both heat conduction pathways and heat cycle resistance, while suppressing coarse compound precipitation at the joint interface that would harm heat conductivity. This local microstructural control resolves the contradiction.
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 exhibits excellent heat cycle resistance, heat conductivity, and wettability, maintaining shear strength residual rates of 40% or more after 3000 cycles in a -40°C to +125°C temperature range, preventing erroneous operations in vehicle-mounted electronic circuits.
Implementation Method 1
the heat conductivity required as a solder joint must not deteriorate in accordance with excessive specifications of the heat cycle resistance... when the wettability of molten solder is poor, heat radiation of the solder joint is poor
Implementation Method 2
When the vehicle-mounted electronic circuit is exposed to a heat-cycle environment, each of the electronic components and the printed circuit board repeats thermal expansion and contraction
Data Source
AI summary
A solder alloy, a solder paste, a solder ball, a solder preform, a solder joint, a vehicle-mounted electronic circuit, an ECU electronic circuit, a vehicle-mounted electronic circuit device, and an ECU electronic circuit device which have a liquidus-line temperature and a solidus-line temperature falling within predetermined temperature ranges, and have excellent heat conductivity and excellent heat cycle resistance. The solder alloy has an alloy composition of, by mass %, Ag: 3.0 to 3.8%, Cu: 0.1 to 1.0%, Bi: more than 0% and 0.9% or less, Sb: 1.0 to 7.9%, Fe: 0.020 to 0.040%, Co: 0.001 to 0.020%, with the balance being Sn. The solder alloy may further contain, by mass %, at least one of Ge, Ga, As, Pd, Mn, In, Zn, Zr, and Mg: 0.1% or less in total.