Pre-Plated Solder Layer for Pressure-Free Diffusion Soldering
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Solution Overview
Problem
The existing diffusion soldering process for semiconductor technologies is costly, requires specialized equipment, and limits throughput due to the need for high mechanical pressure and high soldering temperatures, which are challenging to manage efficiently.
Innovation Solution
A pre-soldered circuit carrier with a metal die attach surface and a plated solder region of specific compositions and thicknesses, allowing for pressure-free diffusion soldering by forming intermetallic phases at elevated temperatures, thereby reducing the need for mechanical pressure and optimizing the soldering process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional diffusion soldering is performed with sputtering solder material onto the wafer backside, then soldering can be achieved, but the process cost increases significantly and throughput is limited due to specialized equipment requirements and mechanical pressure constraints
Solution Approach 1:
The solder layer is pre-applied to the bond pad on the circuit carrier before die attachment, eliminating the need for post-attachment soldering operations. This preliminary action allows the solder to react with the die metallization during the attachment process itself, enabling high-throughput processing without specialized sputtering equipment while maintaining reliable solder joints
Solution Approach 2:
The invention replaces the traditional mechanical pressure-based diffusion soldering system with a chemical reaction-based system. By using a eutectic solder alloy that reacts chemically with the die metallization at elevated temperatures, the process eliminates the need for complex mechanical pressure application systems, enabling simpler, higher-throughput processing
2Strength
If high mechanical pressure is applied to achieve form-fit interconnect during diffusion soldering, then soldering can be completed, but the process requires specialized equipment and limits throughput
Solution Approach 1:
The invention changes the solder alloy composition to a eutectic formulation (e.g., SAC305: Sn-3.0Ag-0.5Cu) with a defined melting point of 88-89°C. This parameter change allows the solder to transition from a solid-state diffusion process requiring high mechanical pressure to a liquid-state reflow process where strong intermetallic bonds form during cooling, eliminating the need for complex pressure application equipment while maintaining interconnect strength
3Loss of time
If high soldering temperature is used to enable full reaction and isothermal solidification in short time, then soldering speed improves, but the process requires specialized equipment and maintains complexity
Solution Approach 1:
The invention utilizes the phase transition of the eutectic solder alloy from solid to liquid at its defined melting point (88-89°C for SAC305). During reflow soldering, the solder melts completely, wets the die metallization, and forms intermetallic compounds. Upon cooling, the liquid solder solidifies into a strong, reliable joint. This controlled phase transition enables rapid soldering at moderate temperatures without requiring complex isothermal heating equipment, reducing both time and equipment 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 approach enables efficient, high-throughput soldering with improved thermal and electrical performance by forming strong intermetallic phases without mechanical pressure, enhancing the reliability and efficiency of the die attach process.
Implementation Method 1
the plated solder region forms one or more intermetallic phases with the die attach surface at a soldering temperature that is above the melting point of the plated solder region
Data Source
AI summary
A pre-soldered circuit carrier includes a carrier having a metal die attach surface, a plated solder region on the metal die attach surface, wherein a maximum thickness of the plated solder region is at most 50 μm, the plated solder region has a lower melting point than the first bond pad, and the plated solder region forms one or more intermetallic phases with the die attach surface at a soldering temperature that is above the melting point of the plated solder region.