Vehicle Windshield Terminal Joint Stress Design for Lead-Free Solder
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Solution Overview
Problem
The use of lead-free solder in joining conductors and terminals in windshields for vehicles leads to residual stress and cracking due to the higher melting point and lower deformability compared to leaded solder, resulting in a decrease in the breaking strength of the glass plate after terminal attachment.
Innovation Solution
A windshield manufacturing method that includes forming a conductor with a terminal joint portion on a glass plate, plastically deforming the surface of the terminal joint portion to create a compressive stress portion, and joining the terminal to the conductor with lead-free solder interposed between them, thereby increasing the breaking strength after terminal attachment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If lead-free solder is used to join conductor and terminal, then environmental safety is improved, but residual stress and cracking occur due to higher melting point and lower deformability
Solution Approach 1:
The patent applies compressive stress to the conductor surface before soldering through shot peening or laser processing. This preliminary action creates a stress state that counteracts the tensile stress generated during subsequent cooling after soldering, preventing cracks and maintaining breaking strength while using lead-free solder
Solution Approach 2:
The patent changes the surface stress state of the conductor from unstressed or tensile to compressive through shot peening or laser processing. This parameter change in stress state allows the conductor to withstand the thermal stress from lead-free soldering without cracking, resolving the contradiction between environmental safety and reliability
2Object-affected harmful factors
If lead-free solder is used instead of leaded solder, then environmental compliance is improved, but breaking strength decreases due to higher elastic modulus and reduced stress absorption
Solution Approach 1:
Compressive stress is applied to the conductor surface before soldering through shot peening or laser processing. This preliminary stress application creates a residual compressive stress field that compensates for the stress concentration that would otherwise occur during cooling, maintaining breaking strength while enabling lead-free solder use
Solution Approach 2:
The surface stress parameter of the conductor is changed from neutral or tensile to compressive through shot peening or laser processing. This parameter change allows the rigid lead-free solder to be used without compromising breaking strength, as the compressive stress counteracts the thermal stress during cooling
3Strength
If solder joining is performed at high temperature to form alloy layer, then joining strength is improved, but thermal stress and residual stress increase causing cracks
Solution Approach 1:
Compressive stress is applied to the conductor surface before soldering through shot peening or laser processing. This preliminary action creates a residual compressive stress field that counteracts the tensile stress generated during high-temperature soldering and subsequent cooling, allowing strong joining without cracks
Solution Approach 2:
The stress state parameter of the conductor is changed to compressive through shot peening or laser processing before soldering. This parameter change enables the conductor to withstand high-temperature soldering cycles without developing harmful residual tensile stress, maintaining both joining strength and structural integrity
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 application of compressive stress to the terminal joint portion through surface polishing reduces residual tensile stress and enhances the breaking strength of the glass plate after terminal attachment, effectively addressing the issues associated with lead-free solder use.
Implementation Method 1
Firing of the silver-containing paste can be implemented simultaneously with thermoforming of the glass plate
Implementation Method 2
When the temperature drops, a difference in thermal expansion coefficient between the glass plate and the solder causes a difference in the amount of thermal contraction between the glass plate and the solder, and causes strain between the glass plate and the solder
Implementation Method 3
In order to join the conductor and the solder sufficiently, it is necessary to heat the solder to its melting point or above
Data Source
AI summary
A windshield for vehicle includes a laminated glass in which a plurality of glass plates are bonded together with an intermediate film interposed therebetween, in which: the laminated glass includes a glass plate with a terminal, the glass plate with the terminal including a glass plate of the plurality of glass plates, a conductor, and the terminal, the conductor being formed on one surface of the glass plate, the conductor including a material containing silver and glass frit, the conductor having a terminal joint portion to which the terminal is joined, the terminal being joined onto the terminal joint portion with lead-free solder interposed therebetween; the conductor includes the terminal joint portion; and at least a surface of the terminal joint portion has a compressive stress portion.