Semiconductor Die Attach Using Thin Preform Diffusion Soldering
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Solution Overview
Problem
The diffusion soldering process for semiconductor die attachment is costly due to significant solder material deposition and requires high force and specialized equipment, limiting throughput and efficiency.
Innovation Solution
A method involving the application of a thin solder preform with a lower melting point than the semiconductor die and substrate, which reacts to form intermetallic phases without direct pressure application, allowing for batch processing and improved solder joint quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional diffusion soldering is used with significant solder material deposition, then reliable electrical connection is achieved, but manufacturing cost increases significantly
Solution Approach 1:
The patent changes the thickness parameter of the solder preform from traditional thick deposition to a thin preform with maximum thickness of 30 μm. This parameter change reduces solder material consumption and deposition cost while maintaining reliable electrical connection through the formation of intermetallic phases that provide adequate electrical conductivity and mechanical bonding.
Solution Approach 2:
The patent employs a composite solder preform structure consisting of a core layer and outer cladding layers. The core layer provides the primary solder material for intermetallic formation, while the outer cladding layers protect the core and facilitate controlled reaction with the semiconductor die and substrate metals, ensuring reliable electrical connection with reduced overall material usage.
2Strength
If high force is applied during die attach to achieve form-fit interconnect, then mechanical bonding is improved, but equipment complexity and specialized machinery requirements increase
Solution Approach 1:
The patent replaces the traditional mechanical pressure application system with a thermal diffusion process. Instead of using complex high-force pressing equipment to achieve form-fit interconnect, the invention uses controlled thermal energy to drive diffusion soldering, where the solder preform reacts with metal regions to form intermetallic phases that provide both mechanical bonding and electrical connection without requiring specialized high-force attachment equipment.
3Reliability
If traditional diffusion soldering process is used, then soldered joint is formed, but processing time increases due to sequential individual die processing
Solution Approach 1:
The patent merges multiple individual die attach processes into a single batch processing operation. By placing multiple semiconductor dies with thin solder preforms on a substrate simultaneously and applying uniform heating, the process forms soldered joints for all dies in parallel rather than sequentially. This merging of operations maintains reliable soldered joint quality through controlled intermetallic phase formation while dramatically improving throughput efficiency and reducing total processing time.
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 reduces costs by enabling efficient batch processing without mechanical pressure, forming high-melting intermetallic phases throughout the soldered joint, enhancing the reliability and efficiency of the die attach process.
Implementation Method 1
forming a soldered joint between the metal region of the semiconductor die and the metal region of the substrate via a diffusion soldering process
Implementation Method 2
the solder preform melts and fully reacts with the metal region of the semiconductor die and the metal region of the substrate
Implementation Method 3
the solder preform melts and fully reacts with the metal region of the semiconductor die and the metal region of the substrate to form one or more intermetallic phases throughout the entire soldered joint
Data Source
Figure 1
Figure 2A~2D
Figure 3
AI summary
A method of joining a semiconductor die (200) to a substrate (202) includes: applying a solder preform (204) to a metal region (212) of the semiconductor die (200) or to a metal region of the substrate (202), the solder preform (204) having a maximum thickness of 30 µm and a lower melting point than both metal regions; forming a soldered joint between the metal region (212) of the semiconductor die (200) and the metal region of the substrate (202) via a diffusion soldering process and without applying pressure directly to the die (200); and setting a soldering temperature of the diffusion soldering process so that the solder preform (204) melts and fully reacts with the metal region (212) of the semiconductor die (200) and the metal region of the substrate (202) to form one or more intermetallic phases throughout the entire soldered joint, each intermetallic phase having a melting point above the melting point of the preform (204) and the soldering temperature.