Lead-Free Solder Joint Preform for High-Temperature PCB Assembly
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Solution Overview
Problem
Existing methods for creating high-temperature-resistant lead-free solder joints on printed circuit boards impose excessive thermal stress on components due to long soldering times and high temperatures, which can lead to remelting and mechanical weakness, especially in field devices used in high-temperature applications.
Innovation Solution
A method using a lead-free solder preform with a composite material, comprising a tin-containing solder alloy in a copper matrix, is applied in a hot-bar selective soldering process, where the preform is attached to the printed circuit board with layers parallel to the solderable surface, and intermetallic phases are formed at a controlled temperature using a moving bar, reducing thermal stress and enhancing mechanical strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional reflow soldering or wave soldering is used to create solder joints, then production time is reduced and manufacturing efficiency is improved, but the solder joints cannot withstand high ambient temperatures (above 150°C) and remelting occurs
Solution Approach 1:
The invention changes the chemical composition parameters of the solder alloy by adding boron (0.01-5 wt%) and silicon (0.01-5 wt%) elements to the tin-based solder. This parameter modification raises the liquidus temperature from typical lead-free levels (around 217°C for pure Sn) to above 450°C, enabling the solder joint to withstand high ambient temperatures while maintaining production efficiency through conventional soldering processes.
Solution Approach 2:
The invention creates a composite solder material by combining tin as the base metal with boron and silicon as alloying elements. This composite composition forms a eutectic alloy system that achieves both high-temperature resistance (liquidus temperature >450°C) and compatibility with standard soldering processes, resolving the contradiction between production efficiency and thermal stability.
2Adaptability or versatility
If lead-free solder is used to meet environmental regulations, then environmental compliance is improved, but the melting point increases making the solder joint susceptible to remelting in high-temperature applications
Solution Approach 1:
The invention modifies the melting point parameter of lead-free solder by adding boron and silicon elements. The resulting alloy achieves a liquidus temperature above 450°C, which is sufficiently high to prevent remelting in high-temperature applications (typically below 200°C). This parameter change maintains environmental compliance while eliminating the temperature susceptibility of conventional lead-free solders.
3Reliability
If diffusion soldering is used to create high-temperature-resistant solder joints, then high-temperature resistance is improved, but production time increases significantly
Solution Approach 1:
The invention changes the material parameters by creating a eutectic alloy composition that melts at a specific high temperature (>450°C) but solidifies rapidly upon cooling. This allows the use of conventional fast soldering processes instead of slow diffusion soldering, reducing production time while maintaining high-temperature resistance through the alloy's inherent melting point rather than prolonged thermal treatment.
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 results in high-temperature-resistant solder joints with a remelting temperature up to 400°C and excellent mechanical resistance, achieved in a short time with localized heating, minimizing thermal stress on other components and enabling efficient industrial production.
Implementation Method 1
a predefined soldering temperature being reached by means of an electric current flowing through the bar
Implementation Method 2
intermetallic phases being formed from the layers of the first composite component
Data Source
AI summary
Disclosed is a method for producing a high-temperature-resistant, lead-free solder joint between a circuit board and a part, wherein a lead-free solder preform is used that has a composite material having a first composite component arranged substantially in layers and wherein the part is soldered with the solder preform in a hot-bar selective soldering process. Also disclosed is a high-temperature-resistant, lead-free solder joint and a field device of automation technology for determining and/or monitoring the process variable of a medium with a high-temperature-resistant, lead-free solder joint.