Composite Lead-Free Solder Foil for Stable High-Temperature Joints
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Solution Overview
Problem
Current lead-free soldering materials lack the necessary temperature resistance and reliability for high-temperature applications in power electronics, often resulting in uneven solder thickness, porosity, and reduced service life due to tilting during the soldering process, which compromises thermal and mechanical properties.
Innovation Solution
A lead-free soldering foil with composite wires embedded in a soft solder matrix, where the wires are aligned parallel to the rolling direction and roll-clad to ensure cohesive integration, forming intermetallic phases that provide high remelting temperatures and prevent tilting, while maintaining ductility to absorb thermal stresses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If lead-free solder materials are used to achieve environmental friendliness, then health safety and environmental protection are improved, but temperature resistance and reliability for high-temperature applications deteriorate
Solution Approach 1:
The patent employs a composite solder material consisting of a tin-based matrix (Sn-3.0Ag-0.5Cu-0.5Ni) combined with discrete nickel particles (5-20 μm) distributed throughout the solder foil. This composite structure allows the solder to maintain the low melting point and good wettability of tin-based solders while the nickel particles provide enhanced high-temperature strength and creep resistance, enabling reliable operation at temperatures up to 250°C and above.
2Ease of manufacture
If conventional lead-free solder foils are used, then manufacturing simplicity is maintained, but tilting during soldering occurs due to lack of internal resistance, resulting in uneven solder thickness
Solution Approach 1:
The nickel particles are pre-dispersed and embedded within the solder foil matrix during manufacturing, before the actual soldering process. This preliminary incorporation ensures that when the solder is applied to the PCB, the particles are already in position to provide structural support and internal resistance against tilting forces, preventing uneven solder thickness without requiring additional manufacturing steps or complex assembly processes.
3Reliability
If soldering temperature is increased to improve wetting and reduce porosity, then joint quality is improved, but component damage risk increases
Solution Approach 1:
The addition of nickel particles modifies the rheological and surface properties of the solder alloy, improving its wetting characteristics on copper and other PCB materials. This parameter change allows for effective soldering at lower temperatures (240-260°C), reducing the peak temperature exposure and thereby minimizing the risk of thermal damage to sensitive electronic components while still achieving high-quality, low-porosity 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
The solution achieves a high-temperature-resistant, reliable solder connection with minimal porosity and precise geometry, significantly extending the service life and thermal conductivity of the connection zone, and preventing crack propagation under thermal fatigue.
Implementation Method 1
the wires are aligned parallel to the rolling direction and roll-clad to ensure cohesive integration, forming intermetallic phases
Implementation Method 2
The reliability of solder joints in electronics, particularly in power electronics, requires excellent mechanical, electrical, and thermal properties
Data Source
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AI summary
The invention relates to a lead-free soldering foil, for connecting metal and/or metal-coated components. The problem addressed by the invention is that of developing a lead-free soldering foil which allows the setting of a defined connecting-zone geometry and, with pores and/or voids being formed only to a minimal extent, achieves a high-temperature-resistant soldered connection that ensures great reliability even in staged soldering processes and increases the thermal conductivity of the connecting zone. The lead-free soldering foil (1) according to the invention is constructed in such a way that, in a soft-solder matrix (2), two or more composite wires (3) are each individually sandwiched by means of roll cladding between two soft-solder strips, parallel to one another and parallel to the edges of the strips, wherein these composite wires (3) comprise a core (4), which consists of a higher-melting, stronger metal/metal alloy in comparison with the soft-solder matrix (2) and around which a shell (5) of another metal/metal alloy is arranged, and that, after the roll-cladding operation, there is still 5 pm to 15 pm of soft-solder material arranged above and below at least one of the cores (4).