Batch Diffusion Soldering of Semiconductor Dies Without Pressure
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Solution Overview
Problem
The existing diffusion soldering process for semiconductor devices is inefficient due to the need for high force application and specialized equipment, which limits throughput and increases costs, especially since the solder deposition is a significant fraction of the wafer cost and requires high temperatures for isothermal solidification.
Innovation Solution
A batch soldering method that uses thin solder preforms, up to 30 µm thick, with a lower melting point than the semiconductor dies and substrates, to form intermetallic phases without direct pressure application, allowing multiple dies to be soldered simultaneously using a single soldering process, and optionally using soft solder pastes for additional joints.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high force is applied during die attach to achieve form-fit interconnect, then bonding strength is improved, but device complexity increases due to specialized equipment and process complexity
Solution Approach 1:
The patent replaces the mechanical pressure application system with a chemical reaction-based bonding system. Instead of using a bond force unit to apply high mechanical force to achieve form-fit interconnect, the invention uses a two-part epoxy paste that cures to form strong chemical bonds, eliminating the need for complex mechanical pressing equipment and force control systems.
Solution Approach 2:
The patent changes the bonding mechanism from mechanical force-dependent to chemistry-dependent by using a two-part epoxy system. The bonding strength is achieved through chemical curing rather than mechanical compression, fundamentally changing the parameter that controls bond formation from applied force to cure time and temperature.
2Reliability
If mechanical pressure is applied to each die individually and maintained until solder solidifies, then bonding reliability is improved, but productivity decreases due to sequential processing
Solution Approach 1:
The patent merges multiple individual die attach operations into a single batch processing step. Multiple dies are placed on the substrate simultaneously, and the epoxy paste cures all bonds at the same time, eliminating the sequential processing required by traditional methods while maintaining bonding reliability through the chemistry-based bonding mechanism that does not require continuous mechanical pressure.
Solution Approach 2:
The patent performs preliminary placement of multiple dies on the substrate before curing, allowing all dies to be positioned and the paste to be applied in advance. The actual bonding occurs automatically during the curing process without requiring continuous monitoring or pressure application, enabling batch processing that improves throughput while maintaining reliability.
3Manufacturing precision
If high soldering temperature is used to enable full reaction and isothermal solidification, then solder joint quality is improved, but energy consumption increases
Solution Approach 1:
The patent changes the soldering process from high-temperature isothermal solidification to a lower-temperature reflow process. The two-part epoxy paste cures at moderate temperatures, and the solder paste is reflowed at lower temperatures than traditional isothermal soldering, reducing energy consumption while maintaining joint quality through controlled chemical curing and selective soldering.
Solution Approach 2:
The patent utilizes the phase transition of the epoxy paste from liquid to solid during curing to achieve bonding, rather than relying solely on isothermal solidification of solder at high temperatures. This phase change occurs at lower temperatures and provides reliable bonding without the high energy input required for traditional isothermal soldering processes.
4Quantity of substance
If thin solder layer is used to achieve form-fit interconnect, then material cost is reduced, but bonding strength decreases requiring high force application
Solution Approach 1:
The patent uses a composite bonding system consisting of two-part epoxy paste and solder paste. The epoxy provides the primary bonding strength through chemical adhesion, while the solder provides electrical and thermal conduction. This composite approach allows the use of minimal solder material for form-fit interconnect while maintaining strong bonding through the epoxy's chemical bonds, eliminating the need for high force application.
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 throughput by eliminating the need for direct pressure application, reduces material costs, and allows for the formation of high-melting-point intermetallic phases throughout the soldered joints, improving thermal and electrical performance while accommodating different semiconductor types and substrates.
Implementation Method 1
the first solder preform melts and fully reacts with the metal region of the first semiconductor die and the first metal region of the substrate to form one or more intermetallic phases throughout the entire first soldered joint
Implementation Method 2
the first solder preform having a maximum thickness of 30 μm and a lower melting point than both the metal region of the first semiconductor die and the first metal region of the substrate; setting a soldering temperature of the soldering process so that the first solder preform melts
Data Source
Figure 1
Figure 2A~2D
Figure 3
AI summary
A method of batch soldering includes: forming a soldered joint (208) between a metal region (212) of a first semiconductor die (200') and a metal region of a substrate (202) using a solder preform via a soldering process which does not apply pressure directly to the first semiconductor die (200'), the solder preform having a maximum thickness of 30 µm and a lower melting point than the metal regions; setting a soldering temperature of the soldering process so that the solder preform melts and fully reacts with the metal region (212) of the first semiconductor die (200') and the metal region of the substrate (202) to form one or more intermetallic phases throughout the entire soldered joint (208), each intermetallic phase having a melting point above the preform melting point and the soldering temperature; and soldering a second semiconductor die (200'') to the same or different metal region of the substrate (200), without applying pressure directly to the second semiconductor die (200'').