Semiconductor Die Solder Joint with Full Intermetallic Diffusion
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Solution Overview
Problem
The existing diffusion soldering process for semiconductor die attachment is costly due to the deposition of a thin solder layer, requires specialized equipment, and limits throughput due to the need for high mechanical pressure and high soldering temperatures, which complicates the formation of a reliable and efficient soldered joint.
Innovation Solution
A method involving the application of a thin solder preform with a lower melting point than the semiconductor die and substrate, which melts and reacts to form intermetallic phases throughout the soldered joint without direct pressure application, allowing for batch processing and improved wettability using formic acid in a vacuum oven.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If a thin sputtered solder layer is used for die attach, then material cost is reduced, but high mechanical force is required to achieve form-fit interconnect
Solution Approach 1:
The patent changes the thickness parameter of the solder layer from thin (sputtered) to thick (preform with 10-100 μm), which fundamentally alters the joining mechanism from mechanical interlocking to diffusion bonding, eliminating the need for high mechanical force during attachment
Solution Approach 2:
The patent replaces the mechanical force-based form-fit interconnect with a thermal diffusion-based bonding process, where the solder preform is heated to melt and diffuse into the metal regions, creating a strong bond without requiring high mechanical pressure
2Strength
If high mechanical pressure is applied to achieve form-fit interconnect, then joint strength is improved, but specialized equipment and process complexity increase
Solution Approach 1:
The patent replaces the mechanical pressure application system with a thermal processing system. Instead of using bond force units and pressure applicators, the process uses a heating system to melt the solder preform and achieve diffusion bonding, significantly simplifying the equipment requirements
Solution Approach 2:
The patent utilizes the phase transition of the solder preform from solid to liquid and back to solid intermetallic phases during heating and cooling. This phase change enables the solder to flow and diffuse into the metal regions, creating strong joints without mechanical pressure
3Reliability
If high soldering temperature is used for full reaction and isothermal solidification, then joint reliability is improved, but throughput is limited due to prolonged pressure maintenance
Solution Approach 1:
The patent performs preliminary action by pre-forming the solder layer with optimal thickness (10-100 μm) before the joining process. This preformed layer ensures complete reaction and intermetallic phase formation during heating, achieving reliable joints without requiring prolonged pressure maintenance, thus improving throughput
4Manufacturing precision
If individual die pressure application is used for soldering, then joint quality is maintained, but processing time increases limiting throughput
Solution Approach 1:
The patent merges multiple individual die processing steps into a single batch processing operation. Multiple dies with solder preforms are heated simultaneously in a furnace or heating chamber, achieving uniform joint quality across all dies without the time penalty of sequential processing
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, simplifies the process by eliminating the need for high-pressure equipment, increases throughput, and ensures a strong, high-melting-point soldered joint with a uniform intermetallic phase, enhancing the thermal and electrical performance of semiconductor devices.
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
allowing for batch processing and improved wettability using formic acid in a vacuum oven
Data Source
AI summary
A semiconductor device includes: a semiconductor die having a metal region; a substrate having a metal region; and a soldered joint between the metal region of the semiconductor die and the metal region of the substrate. One or more intermetallic phases are present throughout the entire soldered joint, each of the one or more intermetallic phases formed from a solder preform diffused into the metal region of the semiconductor die and the metal region of the substrate. The soldered joint has the same length-to-width aspect ratio as the semiconductor die.