Multi-step High Temperature Bonding for Stronger Intermetallic Joints
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Solution Overview
Problem
Conventional high temperature bonding methods using one-step heating result in a weaker bond layer due to the paste impeding the path of the solder, preventing full coating of metal particles and thus hindering the formation of a strengthened bond layer between substrates.
Innovation Solution
A multi-step heating process is employed, where a substrate assembly with an insert holding tin and metal particles is first heated below the melting point of tin to evaporate any paste, followed by heating to the melting point of tin to form intermetallic bonds, allowing capillary forces to draw tin into the bond layer and consume it, thereby forming a stronger bond without paste impedance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If one-step heating is used to bond substrates, then the bonding process is simple and fast, but the paste impedes the solder path and prevents full coating of metal particles, resulting in a weaker bond layer
Solution Approach 1:
The bonding process is divided into multiple heating steps: first heating to evaporate paste, then second heating to melt solder and form intermetallic bonds. This segmentation allows each step to optimize for its specific function, eliminating paste impedance before soldering occurs.
Solution Approach 2:
The first heating step performs preliminary action by evaporating the paste before the soldering process begins. This preliminary removal of paste ensures that the subsequent soldering step can proceed without impedance, allowing complete coating of metal particles.
2Ease of manufacture
If paste is used in the bonding process, then metal particles can be delivered to the bond interface, but the paste creates impedance that prevents solder from fully coating the particles
Solution Approach 1:
The harmful component (paste) is extracted or removed from the system through the first heating step that evaporates it. This leaves only the beneficial metal particles and solder, allowing complete coating without paste impedance.
Solution Approach 2:
The paste, which initially causes harm by impeding solder flow, is converted into a benefit through controlled evaporation. The first heating step utilizes the paste's presence to deliver metal particles, then removes the paste to enable complete solder coating.
3Strength
If heating temperature reaches the melting point of tin, then intermetallic bonds can form, but the paste remains and continues to impede the solder path
Solution Approach 1:
The heating process is segmented into two distinct temperature phases: first heating below the melting point to evaporate paste, then second heating to the melting point and above to form intermetallic bonds. This temporal segmentation ensures paste removal occurs before soldering begins.
Solution Approach 2:
The temperature parameter is changed in two stages: first heated to a lower temperature range for paste evaporation, then increased to the melting point and above for intermetallic bond formation. This parameter progression eliminates paste impedance before high-temperature bonding.
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 method creates a stronger bond layer by ensuring better wetting of particles and preventing paste impedance, resulting in a more robust bond suitable for high temperature applications.
Implementation Method 1
heating the assembly during a first heating to a first temperature that is below the low melting temperature
Implementation Method 2
heating the assembly during a second heating to a second temperature that is approximately equal to the low melting temperature
Implementation Method 3
allowing capillary forces to draw tin into the bond layer and consume it
Data Source
AI summary
A method for high temperature bonding of substrates may include providing a top substrate and a bottom substrate, and positioning an insert between the substrates to form a assembly. The insert may be shaped to hold at least an amount of Sn having a low melting temperature and a gap shaped to hold at least a plurality of metal particles having a high melting temperature greater than the low melting temperature. The assembly may be heated to below the low melting temperature and held for a first period of time. The assembly may further be heated to approximately the low melting temperature and held for a period of time at a temperature equal to or greater than the low melting temperature such that the amount of Sn and the amount of metal particles form one or more intermetallic bonds. The assembly may be cooled to create a bonded assembly.