Isothermal Solidification Bonding for Low-Temperature Joining
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Solution Overview
Problem
Existing methods for connecting parts, such as semiconductor chips and printed circuit boards, face challenges with thermal stability and integrity due to high melting point soldering systems, which can be damaged by subsequent joining steps, and often require expensive noble metals like gold and higher process temperatures.
Innovation Solution
A method using an isothermal solidification process with a bismuth-indium-silver bonding layer, applied through thin layers via physical vapor deposition, which forms a strong, thermally stable connection at low temperatures (up to 120°C) and maintains strength above 260°C, avoiding continuous bismuth layers for enhanced stability and electrical conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high melting point soldering systems are used to connect parts, then the joint strength is improved, but the thermal stability deteriorates because subsequent joining steps can damage the joint
Solution Approach 1:
The patent applies parameter changes by utilizing the phase transition of the In-Bi-Ag alloy system. The bonding layer is designed to be liquid at joining temperatures (above its eutectic point of 101°C) to enable wetting and bonding, then solidifies upon cooling to form a thermally stable joint with melting point above 260°C. This dynamic parameter change resolves the contradiction by providing both strength during/after joining and thermal stability for subsequent processes.
Solution Approach 2:
The patent employs composite materials by creating a multi-layer bonding structure comprising In-Bi-Ag alloy layers combined with barrier metal layers (such as Cu, Ni, Pd, or Pt). This composite structure provides both the low-temperature bonding capability of the eutectic alloy and the thermal stability and oxidation resistance of the barrier metals, enabling the joint to withstand subsequent joining steps at elevated temperatures.
2Reliability
If noble metals like gold are used for connecting parts, then the reliability is improved, but the manufacturing cost increases
Solution Approach 1:
The patent applies this principle by replacing expensive noble metals (gold, platinum) with a cost-effective In-Bi-Ag eutectic alloy system that provides comparable or superior bonding performance. The alloy achieves reliable connections through its unique phase transition properties, eliminating the need for costly noble metals while maintaining connection reliability and thermal stability.
Solution Approach 2:
The patent uses parameter changes by exploiting the eutectic phase transition of the In-Bi-Ag alloy at 101°C. This phase change enables the alloy to be liquid during joining for excellent wetting and bonding, then solidify to form a reliable, thermally stable joint. This mechanism provides noble-metal-level reliability without the associated cost, as the phase transition behavior replaces the need for expensive materials.
3Strength
If high process temperatures are used for soldering, then the bonding strength is improved, but the adaptability deteriorates because thermally sensitive materials cannot be processed
Solution Approach 1:
The patent applies parameter changes by utilizing the phase transition of the In-Bi-Ag eutectic alloy. The bonding process occurs at low temperatures (above 101°C eutectic point) where the alloy is liquid, enabling excellent wetting and bonding strength. Upon cooling, the alloy solidifies to form a thermally stable joint with melting point above 260°C. This dynamic parameter change allows processing of thermally sensitive materials while maintaining strong bonds.
Solution Approach 2:
The patent employs phase transitions as the core mechanism: the In-Bi-Ag alloy transitions from solid to liquid at the eutectic temperature (101°C) during joining, enabling low-temperature bonding of thermally sensitive materials. After bonding, the liquid alloy solidifies upon cooling, creating a thermally stable joint that can withstand subsequent high-temperature processes. This phase transition approach resolves the contradiction between bonding strength and material compatibility.
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 method provides a low-cost, thermally and mechanically stable connection that is resistant to high temperatures, suitable for diverse materials with different thermal expansion behaviors, and eliminates the need for fluxing agents, ensuring durability and cost-effectiveness while maintaining electrical conductivity.
Implementation Method 1
the first layer sequence and the second layer sequence are pressed together at their end faces remote respectively from the first part to be joined and the second part to be joined through application of a joining pressure at a joining temperature for a predetermined joining time. In the process, the first layer sequence and the second layer sequence are at least partly or completely melted and the materials of the two layer sequences mix together.
Implementation Method 2
the first layer sequence and the second layer sequence are at least partly or completely melted and the materials of the two layer sequences mix together
Implementation Method 3
The parts can be joined by means of an isothermic solidifying reaction in order to form an In—Bi—Ag connecting layer
Implementation Method 4
The first layer sequence is applied to the first part to be joined, for example, by physical vapor deposition such as sputtering or vacuum evaporation
Data Source
AI summary
A method is provided for connecting parts to be joined. A first layer sequence is applied to a first part to be joined. The first layer sequence contains silver. A second layer sequence is applied to a second part to be joined. The second layer sequence contains indium and bismuth. The first layer sequence and the second layer sequence are pressed together at their end faces respectively remote from the first part to be joined and the second part to be joined through application of a joining pressure at a joining temperature which amounts to at most 120° C. for a predetermined joining time. The first layer sequence and the second layer sequence fuse together to form a bonding layer which directly adjoins the first part to be joined and the second part to be joined and the melting temperature of which amounts to at least 260° C.