Composite Solder Preform for High-Temperature Reliability
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Solution Overview
Problem
Current high-temperature soldering technologies face challenges with the use of toxic lead-based solders and the high cost of lead-free alternatives, as well as issues with brittleness, low thermal conductivity, and corrosion in existing lead-free solder systems, which limit their effectiveness in applications like die attach and power semiconductor packaging.
Innovation Solution
A laminate composite preform foil is developed, comprising a high-melting ductile metal or alloy core layer sandwiched between low-melting solder layers, which reacts with substrate metals to form high-melting intermetallic compound phases during soldering, resulting in a ductile core layer with IMCs on either side, enhancing the strength and remelt temperature of the solder joint.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high-lead solder alloys (90-95 wt % Pb) are used for high-temperature die attach soldering, then the solder joint achieves high current carrying capability and good thermal conductivity, but the toxicity of lead becomes a harmful factor that is banned in many applications
Solution Approach 1:
The patent uses a composite preform structure consisting of a high-melting-point metal core (such as Ag, Cu, Ni, or their alloys) coated with a low-melting-point solder alloy layer. This composite structure enables the solder joint to achieve high remelt temperature (from the core metal) while using lead-free solder materials, thus eliminating lead toxicity while maintaining structural integrity and thermal/electrical performance.
Solution Approach 2:
The patent changes the melting point parameter of the solder joint by using a high-melting-point core metal (solidus temperature >280°C) instead of relying on high-lead content. This parameter change allows the solder to withstand high reflow temperatures without melting, while the solder layer itself can be lead-free, thus resolving the toxicity issue while maintaining high-temperature performance.
2Object-affected harmful factors
If Pb-free eutectic Au-Sn (280°C), Au-Si (363°C), and Au-Ge (356°C) alloys are used as die attach solders to eliminate lead, then the toxicity issue is resolved, but the cost becomes too high for practical applications
Solution Approach 1:
The patent employs a composite preform with an inexpensive high-melting-point core metal (such as Cu, Ni, or their alloys) combined with a thin layer of solder alloy. This composite approach achieves the desired high remelt temperature and lead-free composition at a much lower cost than using bulk precious metal eutectic solders like Au-Sn or Au-Ge, making the solution economically viable for mass production.
Solution Approach 2:
The patent applies local quality by using a thin solder layer (providing bonding function) combined with a thick core metal layer (providing structural support and high melting point). This localized distribution of materials allows the expensive solder function to be minimized to only where it is needed (at the bonding interface), while the bulk of the joint uses inexpensive high-melting-point metal, thus reducing overall cost while maintaining performance.
3Ease of manufacture
If other high temperature lead-free solders in the Sn-Sb, Bi-Ag, Zn-Sn, and Zn-Al systems are used as candidates, then the cost is reduced, but each system has its own drawbacks such as low solidus temperature, high corrosiveness, or brittleness
Solution Approach 1:
The patent uses a composite preform where the high-melting-point core metal (such as Cu, Ni, or their alloys) provides structural integrity, high remelt temperature, and good ductility, while the solder layer provides bonding capability. This composite approach overcomes the limitations of individual lead-free solder systems by combining materials with complementary properties, achieving a balance of cost, reliability, and performance that neither material could achieve alone.
Solution Approach 2:
The patent changes the effective melting point parameter of the solder joint by using a high-melting-point core metal with solidus temperature >280°C. This allows the use of lower-cost solder alloys in the core while achieving high-temperature performance through the core metal's phase transition behavior, thus resolving the contradiction between cost and reliability.
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 composite preform foil achieves a solder joint with a significantly higher remelt temperature and improved ductility, allowing for reliable bonding of devices without the need for special substrate preparation or high pressures, while maintaining the thermal conductivity benefits of soldering.
Implementation Method 1
the core metal, liquid solder layer, and substrate metals react and consume the low-melting solder phase to form high-melting intermetallic compound phases (IMCs)
Implementation Method 2
the core metal, liquid solder layer, and substrate metals react and consume the low-melting solder phase
Implementation Method 3
During soldering, the core metal, liquid solder layer, and substrate metals react
Implementation Method 4
The resultant solder joint is composed of a ductile core layer sandwiched by the IMCs layers
Data Source
AI summary
Various embodiments of the invention provide laminate composite preform foils for high-temperature Pb-free soldering applications. The laminate composite preform foil is composed of a high-melting, ductile metal or alloy core layer and a low-melting solder coating layer at either side of the core layer. During soldering, the core metal, liquid solder layer, and substrate metals react and consume the low-melting solder phase to form high-melting intermetallic compound phases (IMCs). The resultant solder joint is composed of a ductile core layer sandwiched by the IMCs layers at substrate sides. The joint has a much higher remelt temperature than the original melting temperature of the initial solder alloy coating, allowing subsequent mounting of packaged devices.