Surface-Profiled Solder Preform for Pressure-Free Diffusion Bonding
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Solution Overview
Problem
Current diffusion soldering techniques face challenges in throughput due to the need for mechanical pressure and high soldering temperatures, while mechanical pressure-free methods can impact the quality of soldered joints.
Innovation Solution
A mechanical pressure-free diffusion soldering process using a solder preform with a varying surface profile that creates voids between the substrate and semiconductor die, allowing for improved wetting and intermetallic phase formation without mechanical pressure, utilizing pre-soldering steps like conditioning and activation in a soldering furnace.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If mechanical pressure is applied during diffusion soldering, then solder reflow and isothermal solidification can be achieved, but throughput is limited and high soldering temperatures are required
Solution Approach 1:
The patent replaces the mechanical pressure application system with a chemical activation system. Instead of using mechanical pressure to drive diffusion soldering, the invention uses chemical activation through pre-soldering treatment (conditioning and activation steps) to enable the solder preform to react with the metal joining surfaces, achieving reliable solder joints without mechanical pressure and thus enabling higher throughput
Solution Approach 2:
The patent applies preliminary chemical treatment to the solder preform and metal joining surfaces before the actual soldering process. The conditioning step prepares the surfaces by removing contaminants, and the activation step creates a reactive state that enables diffusion bonding without mechanical pressure, allowing for faster processing and improved throughput
2Productivity
If mechanical pressure-free diffusion soldering is used, then throughput can be increased, but the quality of soldered joints is impacted
Solution Approach 1:
The patent changes the chemical parameters of the solder preform and processing environment to enable pressure-free soldering. By controlling the composition of the solder preform (specific metal content), the atmosphere in the furnace (formic acid vapor), and the temperature profile during conditioning and activation, the invention achieves reliable solder joints without mechanical pressure, thus maintaining both high throughput and joint quality
Solution Approach 2:
The patent introduces formic acid vapor as an intermediary substance that facilitates the chemical reaction between the solder preform and metal joining surfaces. The formic acid vapor acts as a mediator that enables activation and diffusion bonding without requiring direct mechanical contact or pressure, allowing for pressure-free soldering with maintained joint quality
3Reliability
If a varying surface profile is created on the solder preform, then wetting and intermetallic phase formation are improved, but the device complexity increases
Solution Approach 1:
The patent applies local quality by creating a varying surface profile (ridges and channels) on specific regions of the solder preform surface. This localized structural variation enhances wetting and intermetallic phase formation at the interface between the solder preform and metal joining surfaces, while the rest of the solder preform maintains its simple planar structure, thus limiting the increase in overall device complexity
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 enhances the quality of soldered joints by facilitating better wetting and forming intermetallic phases with high tensile strength, improving thermal durability and reducing the need for mechanical pressure, thus increasing throughput and joint reliability.
Implementation Method 1
one or both of the first interface surface and the second interface surface has a varying surface profile that creates voids between the solder preform and one or both of the substrate and the semiconductor die before the melting of the solder preform
Implementation Method 2
performing a mechanical pressure-free diffusion soldering process that forms a soldered joint between the substrate and the semiconductor die by melting the solder preform and forming intermetallic phases in the soldered joint
Implementation Method 3
performing a mechanical pressure-free diffusion soldering process that forms a soldered joint between the substrate and the semiconductor die by melting the solder preform and forming intermetallic phases in the soldered joint
Implementation Method 4
The ridges and channels facilitate outgassing of the arrangement during pre-soldering steps
Data Source
AI summary
A method of soldering includes providing a substrate having a first metal joining surface, providing a semiconductor die having a second metal joining surface, providing a solder preform having a first interface surface and a second interface surface, arranging the solder preform between the substrate and the semiconductor die such that the first interface surface faces the first metal joining surface and such that the second interface surface faces the second metal joining surface, and performing a mechanical pressure-free diffusion soldering process that forms a soldered joint between the substrate and the semiconductor die by melting the solder preform and forming intermetallic phases in the solder. One or both of the first interface surface and the second interface surface has a varying surface profile that creates voids between the solder preform and one or both of the substrate and the semiconductor die before the melting of the solder preform.