Composite Lead-Free Solder Joint for High-Temperature PCB Assembly
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Solution Overview
Problem
Existing soldering techniques for circuit boards in high-temperature applications, such as field devices in automation technology, face challenges in achieving high-temperature-resistant lead-free solder connections while minimizing thermal stress on the entire circuit board, especially when exposed to temperatures above 150°C and requiring sufficient mechanical strength against vibrations.
Innovation Solution
The method combines a lead-free solder molding with a copper matrix and the iron-on selective soldering process, allowing for the formation of intermetallic phases in a short time with localized heating, reducing thermal stress and enabling high-temperature-resistant solder connections through the use of a bracket with a holding force to accelerate phase formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If conventional reflow soldering is used to create lead-free solder connections, then the solder joints can be formed efficiently, but the solder joints cannot withstand temperatures above 150°C due to the low melting point of lead-free solder
Solution Approach 1:
The patent uses a composite solder structure consisting of a lead-free solder alloy core surrounded by a copper matrix. The copper matrix acts as a protective shell that prevents the lead-free solder from melting at high temperatures, while still allowing metallurgical bonding to occur. This composite structure enables the solder joint to withstand temperatures above 150°C without losing integrity.
Solution Approach 2:
The patent changes the physical and chemical parameters of the solder joint by forming intermetallic phases (such as Cu6Sn5 and Cu3Sn) at the interface between the copper matrix and the solder alloy. These intermetallic phases have high melting points and provide thermal stability, transforming the solder joint from temperature-sensitive to temperature-resistant.
2Temperature
If diffusion soldering is used to create high-temperature-resistant solder joints, then the solder joints can withstand high temperatures, but the production time is excessively long making it unsuitable for industrial production lines
Solution Approach 1:
The patent prepares the solder connection by pre-forming a copper matrix structure and positioning the lead-free solder alloy within it before the actual soldering process. This preliminary preparation allows the subsequent soldering step to proceed quickly while still achieving the desired high-temperature resistance through controlled intermetallic phase formation.
Solution Approach 2:
The patent replaces the time-consuming thermal diffusion process with a mechanically assisted soldering approach. By applying pressure and using a specially designed soldering iron that facilitates rapid intermetallic phase formation, the process achieves high-temperature resistance in seconds rather than hours, making it suitable for industrial production.
3Object-affected harmful factors
If selective soldering is used to minimize thermal stress on the circuit board, then adjacent components are protected from thermal damage, but the soldering process becomes more complex and time-consuming
Solution Approach 1:
The patent applies the high-temperature resistant solder structure selectively only to those solder joints that require temperature resistance (e.g., connections near heat-generating components), while other solder joints can use conventional lead-free solder. This localized application reduces overall thermal stress on the circuit board without requiring complex selective soldering processes for all joints.
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 connections with a reflow temperature of up to 400°C, providing excellent mechanical resistance and significantly reducing thermal stress on adjacent components, suitable for industrial production lines with faster production times and minimal thermal impact on other components.
Implementation Method 1
intermetallic phases which extend essentially across the entire thickness of the solder joint in a layered structure
Implementation Method 2
method for producing a high-temperature-resistant lead-free solder connection
Implementation Method 3
an iron is pressed onto the solder joint and the specified soldering temperature is achieved by means of an electric current flowing through the iron
Implementation Method 4
localized heating
Data Source
Figure 1a~1c
Figure 2a~3
AI summary
The invention relates to a method for producing a high-temperature-resistant lead-free solder joint (7; 71) between a circuit board (1) and a part (2; 2b), wherein a lead-free solder preform (3; 3b) is used that has a composite material having a first composite component (VK1) arranged substantially in layers; and wherein the part (2; 2b) is soldered with the solder preform (3; 3b) in a hot-bar selective soldering process. The invention also relates to a high-temperature-resistant lead-free solder joint (7; 71) and to a field device (8) of automation technology for determining and/or monitoring the process variable of a medium with a high-temperature-resistant solder joint (7; 71).