Mixed Alloy Solder Paste High-Temperature Reliability
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current high-temperature Pb-free solders for electronic applications face challenges such as inadequate melting temperature, poor wetting, and weak bonding due to oxidation and reaction chemistry issues, particularly with substrates like Cu and Ni, limiting their reliability and industrial acceptance.
Innovation Solution
The development of mixed alloy solder pastes comprising a primary high-melting solder alloy and a secondary additive alloy that melts first, improving wetting and forming a controlled intermetallic compound layer, enhancing bonding strength and reliability by modifying reaction chemistry and wetting performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If Zn-based alloys (e.g., Zn-Al, Zn-Al-Mg, Zn-Al-Cu) are used to achieve melting temperature above 330°C, then high temperature resistance is improved, but wetting performance deteriorates due to high affinity to oxygen
Solution Approach 1:
The patent introduces a flux composition containing organic carboxylic acid and its ester as intermediary substances that mediate between the Zn-based solder alloy and the metallization surface. The flux contains 5-20 wt% organic carboxylic acid (e.g., formic acid, acetic acid, propionic acid) and 5-30 wt% its ester (e.g., methyl formate, ethyl acetate, isopropyl propionate), which act as wetting agents to overcome the poor wetting caused by oxygen affinity of Zn, Al, and Mg elements.
2Strength
If Sn-Sb alloys with less than 10 wt% Sb are used to maintain good mechanical properties, then mechanical strength is improved, but melting temperature deteriorates (solidus temperature no higher than 250°C)
Solution Approach 1:
The patent creates a composite solder system by combining Zn-based alloy particles (60-95 wt%, providing high melting temperature above 330°C) with Sn-Sb alloy particles (5-40 wt%, providing good mechanical properties and controlled IMC formation). This composite structure allows the Zn-based phase to provide high temperature resistance while the Sn-Sb phase contributes to mechanical strength and reacts with metallization surfaces to form appropriate intermetallic compounds.
3Temperature
If Zn-(20-40 wt%)Sn solder alloys are used to achieve liquidus temperature above 300°C, then high temperature resistance is improved, but reliability deteriorates due to semi-solid state at 260°C causing solder flow out
Solution Approach 1:
The patent modifies the composition parameters of the solder alloy by using Zn-based alloys with specific compositions (Zn-Al, Zn-Al-Mg, or Zn-Al-Cu) that have liquidus temperatures above 330°C, ensuring complete solidification before typical reflow temperatures. The flux composition is also adjusted to contain 5-20 wt% organic carboxylic acid and 5-30 wt% ester, which helps control the melting and solidification behavior during reflow processes.
4Reliability
If Eutectic Au-Sn is used to achieve melting temperature of 280°C and excellent corrosion resistance, then reliability is improved, but cost deteriorates (extremely high cost)
Solution Approach 1:
The patent replaces expensive Au-Sn eutectic solder with a cost-effective Zn-based solder alloy system combined with a specifically formulated flux. The Zn-based alloy (60-95 wt%) combined with Sn-Sb (5-40 wt%) and the organic carboxylic acid/ester flux provides a economical alternative that achieves comparable or superior performance through controlled intermetallic compound formation and improved wetting, eliminating the need for costly precious metals.
5Temperature
If Bi-Ag alloys are used to achieve solidus temperature of 262°C, then melting temperature requirement is satisfied, but bonding strength deteriorates due to weak bonding interface
Solution Approach 1:
The patent introduces Sn-Sb alloy particles (5-40 wt%) as intermediary reactive phase that mediates between the Bi-Ag solder matrix and the metallization surface. The Sn component reacts with Cu and Ni surfaces to form strong intermetallic compounds (Cu6Sn5, Cu3Sn, Ni3Sn4), while the Sb component controls IMC morphology and distribution, thereby significantly improving bonding interface strength compared to Bi-Ag alone.
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 mixed alloy solder pastes achieve improved wetting and bonding strength on various metallization surfaces, maintaining high-temperature reliability and reducing the risk of functional failure during reflow processes, addressing the limitations of existing Pb-free solders.
Implementation Method 1
the additives improve reaction chemistry and wetting on metallization surfaces
Implementation Method 2
the additives improve reaction chemistry and wetting on metallization surfaces, forming well-controlled intermetallic compounds (IMCs)
Implementation Method 3
forming well-controlled intermetallic compounds (IMCs) to enhance bonding strength and reliability
Data Source
AI summary
A solder paste consists of an amount of a first solder alloy powder between 44 wt % to less than 60 wt %; an amount of a second solder alloy powder between greater than 0 wt % and 48 wt %; and a flux; wherein the first solder alloy powder comprises a first solder alloy that has a solidus temperature above 260° C.; and wherein the second solder alloy powder comprises a second solder alloy that has a solidus temperature that is less than 250° C. In another implementation, the solder paste consists of an amount of a first solder alloy powder between 44 wt % and 87 wt %; an amount of a second solder alloy powder between 13 wt % and 48 wt %; and flux.