Lead-Free Solder Alloy for Crack-Resistant Automotive Glass
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Solution Overview
Problem
The challenge is to develop a lead-free solder composition for electrical terminals on tempered automotive glass that is cost-effective and does not cause glass cracking, while maintaining high thermal stability and electrical conductivity, as existing indium-based solders are expensive and high-tin solders with stainless steel bases have drawbacks such as narrow processing windows and increased cracking risks.
Innovation Solution
A solder alloy composition consisting of 15% to 28% indium, 5% to 20% zinc, 1% to 6% silver, and the remaining weight as tin, applied to a copper-based material with an iron-nickel alloy layer, which is soldered to a silver-based connection pad on the glass surface, optimizing the coefficient of thermal expansion and reducing glass cracking propensity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If indium-based lead-free solder is used, then resistance to cracking is improved, but cost increases significantly
Solution Approach 1:
The patent changes the compositional parameters of the solder alloy by reducing indium content from high levels (>50%) to a specific range (15-28%), and introduces zinc (5-20%) and silver (1-6%) as additional alloying elements. This parameter optimization achieves cost reduction while maintaining adequate cracking resistance through the synergistic effect of the multi-element composition.
Solution Approach 2:
The invention creates a composite solder alloy system combining tin, indium, zinc, and silver in specific proportions. This composite material approach leverages the advantages of each element: tin provides base strength and low cost, indium contributes to cracking resistance, zinc enhances fluidity and reduces oxidation, and silver improves strength and electrical conductivity, achieving a balanced performance at reduced cost.
2Ease of manufacture
If high tin solder with stainless steel base is used, then cost is reduced, but glass cracking risk increases and processing window narrows
Solution Approach 1:
The patent modifies the solder composition parameters by limiting tin content to 72-85% (rather than 98%) and adding controlled amounts of indium (15-28%), zinc (5-20%), and silver (1-6%). This compositional adjustment broadens the processing temperature window and reduces thermal stress on the glass, thereby decreasing cracking risk while maintaining cost effectiveness.
Solution Approach 2:
The invention introduces zinc and silver as intermediary elements that mediate between the tin base and the glass substrate. Zinc reduces oxidation and improves wetting characteristics, while silver enhances strength and electrical properties. These intermediary elements create a more compatible interface with the glass, reducing thermal stress and cracking propensity.
3Reliability
If indium content is increased above 50%, then cracking resistance is improved, but cost becomes prohibitive for regular production
Solution Approach 1:
The patent optimizes the indium content parameter to a specific range (15-28%) rather than using high indium content (>50%). This parameter reduction directly lowers material cost while the addition of zinc and silver compensates for any loss in cracking resistance, maintaining adequate reliability at production-friendly cost levels.
Solution Approach 2:
The invention partially replaces expensive indium with more cost-effective elements like zinc and silver. While indium provides superior cracking resistance, the patent uses a balanced approach where moderate indium content combined with other elements achieves sufficient performance at lower cost, making the solder economically viable for regular production applications.
4Ease of manufacture
If high tin solder is used, then cost is reduced, but processing temperature window becomes narrow requiring additional process steps
Solution Approach 1:
The patent adjusts the compositional parameters to create a eutectic or near-eutectic alloy system with a broadened melting range. The specific combination of tin (72-85%), indium (15-28%), zinc (5-20%), and silver (1-6%) creates favorable solidus-liquidus temperature separation, providing a wider processing window that eliminates the need for complex preheating and controlled cooling steps required by high-tin solders.
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 proposed solder alloy effectively reduces glass cracking and maintains high thermal stability, passing environmental exposure tests up to 150°C without failure, while being more cost-effective than indium-based alloys and avoiding the limitations of high-tin solders with stainless steel bases.
Implementation Method 1
optimizing the coefficient of thermal expansion and reducing glass cracking propensity
Implementation Method 2
maintains high thermal stability, passing environmental exposure tests up to 150°C without failure
Implementation Method 3
maintains high thermal stability and electrical conductivity
Data Source
AI summary
An electrical assembly includes an electrical connector soldered to a conductive pad disposed on a glass surface by a solder alloy consisting essentially of 17% to 28% indium by weight, 12% to 20% zinc by weight, 1% to 6% silver by weight, 1% to 3% copper by weight, and a remaining weight of the solder alloy being tin.