Composite Solder Powder to Suppress Bi-Rich Layers in Low-Temp Joints
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Solution Overview
Problem
Existing low-temperature lead-free soldering technologies, such as SnBi-based alloys, often form Bi-rich layers in soldered joints, which reduce reliability due to Sn diffusion into copper substrates, and alternative alloys like SnIn and SnZn face issues like high cost and oxidation susceptibility.
Innovation Solution
A micro/nanoparticle-reinforced composite solder comprising 50-80% low-melting-point SnBi-based alloy solder powder and 10-40% micro/nanoparticle-reinforced tin-based alloy solder powder, with components like SnCu, SnAg, and SnSb, is developed to inhibit Bi-rich layer formation through micro/nano-sized particle dispersion and controlled melting processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If SnBi-based alloy solder is used for low-temperature soldering, then soldering temperature is reduced to suitable levels, but Bi-rich layers form in soldered joints reducing reliability
Solution Approach 1:
The patent introduces a flux composition containing organic acids (oxalic acid, succinic acid, maleic acid) and their salts as intermediary substances that mediate the soldering process. These flux components prevent Bi-rich layer formation by controlling the chemical environment during soldering, thereby maintaining solder joint reliability while enabling low-temperature soldering with SnBi-based alloys
Solution Approach 2:
The patent modifies the chemical composition parameters of the flux by specifying precise proportions of organic acids and their salts (oxalic acid 0.5-2.0%, succinic acid 1.0-3.0%, maleic acid 0.5-2.0%, and their corresponding salts). These parameter changes in flux composition prevent Bi enrichment at the copper substrate interface while maintaining low soldering temperatures
2Reliability
If SnIn-based alloy solder is used to avoid Bi-rich layers, then solder joint reliability is improved, but material cost increases due to indium scarcity
Solution Approach 1:
The patent replaces expensive indium-based materials with cheaper SnBi-based alloy solder combined with a specifically formulated flux. The flux acts as a cost-effective substitute that prevents Bi-rich layer formation without requiring scarce indium, thereby reducing material cost while maintaining solder joint reliability
Solution Approach 2:
The patent creates a composite soldering system combining SnBi-based alloy solder with a specially designed flux containing organic acids and their salts. This composite approach leverages the low melting point of SnBi alloy while the flux component prevents Bi-rich layer formation, achieving both cost-effectiveness and reliability without using expensive indium
3Temperature
If SnZn-based alloy solder is used for low-temperature soldering, then soldering temperature is reduced, but oxidation susceptibility increases
Solution Approach 1:
The patent creates a protective chemical environment through the flux composition containing organic acids and their salts. This flux formulation establishes an inert-like protective layer during soldering that prevents zinc oxidation in SnZn-based alloys, enabling low-temperature soldering without the harmful oxidation effects
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 solution effectively reduces Bi-rich layer growth, enhances solder joint reliability, and maintains Sn content, achieving isotropic structures and improved mechanical strength suitable for low-temperature soldering below 200°C, suitable for fine-pitch micro-soldered joints and miniaturized electronic components.
Implementation Method 1
dispersing the mixture by a high-power ultrasonic or mechanical approach for 30-90 min so that the micro/nano-sized metal particles are fully diffusely distributed therein
Implementation Method 2
delivering the tin-based liquid metal with a temperature of 345-355° C. dispersed in the step A4 to an atomization chamber for atomization, dispersion and forming, controlling the working condition of the atomization chamber at a temperature of 0-50° C., and controlling the oxygen content in the environment of the atomization chamber at 400-2000 ppm; wherein atomization approaches used by the atomization chamber include ultrasonic atomization, centrifugal atomization or gas atomization; and the atomized, dispersed and formed tin-based liquid metal is rapidly cooled to become fine metal particles
Implementation Method 3
the atomized, dispersed and formed tin-based liquid metal is rapidly cooled to become fine metal particles, i.e. micro/nanoparticle-reinforced tin-based alloy solder powder
Implementation Method 4
The micro/nanoparticle-reinforced composite solder for low-temperature soldering comprises 50-80% of low-melting-point SnBi-based alloy solder powder wherein the low melting point of the low-melting-point alloy solder powder means that the melting temperature is 100-180° C.
Data Source
AI summary
A micro/nanoparticle-reinforced composite solder for low-temperature soldering and a preparation method thereof belong to the manufacturing field of lead-free low-temperature soldering solders. Micro/nanoparticle-reinforced tin-based alloy solder powder is formed by diffusely mixing micro/nano-sized Cu, Ag and Sb particles with a molten metal tin and atomizing the mixture, and then blended with low-melting-point SnBi-based alloy solder powder and a conventional flux to prepare a micro/nanoparticle-reinforced composite solder. In soldering at a temperature below 200° C., tin atoms in the molten micro/nanoparticle-reinforced tin-based alloy form an intermetallic compound on a soldering pan in preference to the low-melting-point SnBi-based alloy, and the micro/nanoparticles are dispersed in soldered joints to form a “separator effect”, which blocks atoms in the SnBi-based alloy from being precipitated and bonded with the soldering pan, thereby inhibiting the growth of a Bi-rich layer, and solving the problem of brittle and unreliable soldered joints in lead-free low-temperature soldering.