Profiled Solder Preform for Pressure-Free Die Attach
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Solution Overview
Problem
Current diffusion soldering techniques face challenges with mechanical pressure limitations, high soldering temperatures, and quality issues in forming high-performance soldered joints for semiconductor devices, particularly due to the need for mechanical pressure application and potential sealing effects at low solder preform thicknesses.
Innovation Solution
A mechanical pressure-free diffusion soldering method using a solder preform with a varying surface profile that creates voids between the substrate and semiconductor die, allowing for outgassing and enhanced wetting, involving pre-soldering steps like tacking agent removal and de-oxidation with formic acid introduction, to form intermetallic phases with higher melting points.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If mechanical pressure is applied during diffusion soldering, then soldering speed and throughput are improved, but the semiconductor die may be damaged and process complexity increases
Solution Approach 1:
The patent replaces the mechanical pressure application system with a chemical reaction-based system. Instead of using mechanical pressure to drive diffusion, the invention uses controlled chemical reactions between the solder preform and metal surfaces to achieve bonding without direct mechanical contact with the die, thereby maintaining throughput while protecting die integrity.
Solution Approach 2:
The patent introduces a solder preform as an intermediary material between the substrate and semiconductor die. This preform facilitates the bonding process through controlled chemical reactions and phase changes, eliminating the need for direct mechanical pressure application to the die while still achieving strong joint formation.
2Manufacturing precision
If solder preform thickness is reduced to improve joint quality, then finer intermetallic phases are formed, but sealing effects prevent outgassing and reduce wetting quality
Solution Approach 1:
The patent employs a solder preform with a porous or textured surface structure that maintains controlled thickness for fine intermetallic phase formation while incorporating pathways or channels that prevent sealing effects. This porous structure allows outgassing to occur during the soldering process while still achieving the desired fine intermetallic phase distribution for high-quality joints.
Solution Approach 2:
The patent segments the solder preform thickness into varying regions, with thinner areas that promote fine intermetallic phase formation and thicker or porous areas that provide outgassing pathways. This segmentation allows simultaneous achievement of fine phase control and prevention of sealing effects different parts of the preform.
3Reliability
If soldering temperature is increased to achieve full reaction, then intermetallic phase formation is improved, but energy consumption increases and die damage risk increases
Solution Approach 1:
The patent optimizes the soldering temperature parameter to achieve full chemical reaction and intermetallic phase formation at lower temperatures than conventional methods. By controlling the chemical composition of the solder preform and reaction conditions, the process achieves complete bonding reactions at reduced temperatures, lowering energy consumption while maintaining joint quality and reducing die damage risk.
Solution Approach 2:
The patent performs preliminary preparation of the solder preform and metal surfaces before the actual soldering process, including surface activation and pre-heating steps. This preliminary action ensures that when the soldering process begins, the chemical reactions proceed efficiently at lower temperatures, reducing overall energy consumption while achieving complete intermetallic phase formation.
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 approach improves the quality and reliability of soldered joints by forming intermetallic phases with higher melting points, enhancing thermal and mechanical durability without the need for mechanical pressure, thus addressing throughput and joint quality issues.
Implementation Method 1
Diffusion soldering is one such die attach process
Implementation Method 2
the solder preform melts and fully reacts with the metal region of the first semiconductor die and the metal region of the substrate to form one or more intermetallic phases
Implementation Method 3
forming a soldered joint between a metal region of a first semiconductor die and a metal region of a substrate using a solder preform via a soldering process
Implementation Method 4
both of the first interface surface and the second interface surface have a varying surface profile that creates voids between the solder preform and both of the substrate and the semiconductor die before the melting of the solder preform
Implementation Method 5
de-oxidation with formic acid introduction
Data Source
Figure 1A~1D
Figure 2
Figure 3
AI summary
A method of soldering a semiconductor device includes providing a substrate (102) having a first metal joining surface (106), providing a semiconductor die (104) having a second metal joining surface (114), providing a solder preform (100) having a first interface surface (110) and a second interface surface (112), arranging the solder preform (100) between the substrate (102) and the semiconductor die (104) such that the first interface surface (110) of the solder preform (100) faces the first metal joining surface (106) of the substrate (102) and such that the second interface surface (112) of the solder preform (100) faces the second metal joining surface (114) of the semiconductor die (104), and performing a mechanical pressure-free diffusion soldering process that forms a soldered joint between the substrate (102) and the semiconductor die (104) by melting the solder preform (100) and forming intermetallic phases in the solder. One or both of the first interface surface (110) and the second interface surface (112) has a varying surface profile (124) that creates voids (126) between the solder preform (100) and one or both of the substrate (102) and the semiconductor die (104) before the melting of the solder preform (100). The varying surface profile (124) may comprise a plurality of ridges (128) and channels (130) that are disposed between immediately adjacent ones of the ridges (128), wherein the channels (130) create the voids (126) in the arrangement (116) of the solder preform (100) in between the substrate (102) and the semiconductor die (104), permitting ingress and egress of the ambient atmosphere (122) within a soldering furnace (118) that contains the arrangement (116) of the solder preform (100) in between the substrate (102) and the semiconductor die (104). Performing the mechanical pressure-free diffusion soldering process may comprise a conditioning step that removes a tacking agent (108) provided between the solder preform (100) and one or both of the substrate (102) and the semiconductor die (104), wherein vapours of the tacking agent (108) may be outgassed through the channels (130). Performing the mechanical pressure-free diffusion soldering process may also comprise an activation step that introduces formic acid into the soldering furnace (118), wherein the formic acid can flow into the arrangement (116) through the channels (130) and the resulting reacted oxide can exit the arrangement (116) via the channels (130). The ridges (128) and channels (130) may have an undulating profile along a cross-section of the solder preform (100) that is orthogonal to the ridges (128).