Lead-Free Soldering Process for Automotive Glass
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Solution Overview
Problem
Existing methods for lead-free soldered connections, particularly in automotive glazing, face issues such as mechanical stress leading to glass breakage due to thermal expansion mismatches and inefficient heat transfer, resulting in longer cycle times and energy expenditure, along with poor bonding and risk of solder splashing.
Innovation Solution
A method involving a lead-free soldering process with a flux, where joining partners are heated in three distinct temperature phases: below the solder activation temperature, above the flux activation temperature, and with increased thermal power to accelerate adhesion, using a metallic surface on glass and an iron-nickel alloy connection, ensuring uniform solder fillet formation and reduced thermal stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If lead-free solder alloys are used, then environmental compliance and safety are improved, but bonding quality and mechanical strength deteriorate
Solution Approach 1:
The invention changes the chemical composition parameters of the solder alloy by adding specific elements (Bi, Ag, Cu, Zn, Al, Si, or Ge) to the base Sn-Pb-free solder. These compositional modifications improve wetting behavior and bonding strength while maintaining lead-free status, directly resolving the contradiction between environmental compliance and bonding quality.
Solution Approach 2:
The invention creates a composite solder material by combining Sn with multiple alloying elements (Bi, Ag, Cu, Zn, Al, Si, Ge) in specific ranges. This composite approach leverages the beneficial properties of each element to achieve both environmental compliance and superior bonding performance that pure Sn or simple alloys cannot provide.
2Stability of the object's composition
If iron-nickel alloys or stainless steels are used instead of copper, then thermal expansion compatibility with glass is improved, but thermal conductivity deteriorates
Solution Approach 1:
The invention modifies the electrical connection material composition by specifying Fe-Ni alloys with controlled Ni content (5-30%) or stainless steels with specific Cr and Ni ranges. These compositional adjustments optimize the balance between thermal expansion compatibility with glass and acceptable thermal conductivity, resolving the contradiction between stability and energy efficiency.
Solution Approach 2:
The invention applies different material properties to different parts of the system: the electrical connection material is specifically designed for thermal expansion compatibility with glass, while the solder alloy is optimized for bonding performance. This local optimization allows each component to excel at its specific function without compromising the other.
3Productivity
If heating power is increased to improve heat transfer, then soldering speed is improved, but glass breakage risk increases
Solution Approach 1:
The invention applies flux to the joint area before heating, which prepares the surface for soldering and lowers the required heating temperature. The solder alloy is also pre-configured with optimal composition to reduce melting temperature and improve flow characteristics, allowing effective soldering at lower temperatures that prevent glass breakage while maintaining productivity.
Solution Approach 2:
The invention changes the thermal parameters of the system by using a solder alloy with lowered melting point (through Bi and other elements) and optimizing the heating profile. This allows achieving complete soldering at lower peak temperatures, thereby improving productivity without increasing glass breakage risk.
4Strength
If cycle time is extended to improve heat transfer, then bonding quality is improved, but productivity deteriorates
Solution Approach 1:
The invention changes the chemical composition of the solder alloy to include elements that improve wetting speed and bonding performance (Bi, Ag, Cu, Zn, Al, Si, Ge). These compositional changes enable high-quality bonding to be achieved in shorter times, resolving the contradiction between bonding quality and productivity by reducing the required cycle time through material optimization.
Solution Approach 2:
The invention uses flux as an intermediary substance that facilitates the bonding process. The flux activates the solder and improves wetting behavior, allowing high-quality bonds to form more quickly. This intermediary action reduces the time required for bonding while maintaining or improving bond quality, thereby resolving the contradiction between strength and productivity.
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
This approach enhances the adhesion of solder to silver printing surfaces, reduces glass stress, and shortens the soldering cycle time, improving mechanical and electrical strength while minimizing the risk of glass breakage.
Implementation Method 1
a flux is used to activate the solder
Implementation Method 2
the electrical and mechanical connection is made by a soldering process by means of the action of heat and melting of the solder
Implementation Method 3
melting of the solder/flux mixture including the subsequent cooling phase
Implementation Method 4
melting of the solder/flux mixture including the subsequent cooling phase
Implementation Method 5
the expansion behaves differently when the temperature changes than that of the glass, due to the corresponding expansion coefficient
Data Source
Figure 1~2
Figure 3
AI summary
The invention relates to a method for carrying out solder connections in a technologically optimized manner, in particular lead-free solder connections. At least one of the joining partners provides the solder required for the connection. A flux is used in order to activate the solder, and the electric and mechanical connection is carried out by means of a soldering process under the effect of heat and by melting the solder/flux mixture with the inclusion of a subsequent cooling phase. According to the invention, the joining partners and the solder are heated to a temperature below the activation temperature of the solder and the flux in a first temperature treatment phase. Another heating process is then carried out to a temperature above the activation temperature of the flux up to the upper melting range of the solder in a second temperature treatment phase, wherein the solder melts and begins to connect to the respective joining partners. Furthermore, the thermal output previously applied is increased by an additional 5% to 30% in a third temperature treatment phase in order to accelerate the adhesion behavior of the joining partners.