Copper Terminal Bonding Structure for Stable Fiber Laser Joining
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Solution Overview
Problem
Semiconductor devices face challenges in maintaining high reliability and durability of wiring connections, particularly in high-temperature environments, due to variations in bonding strength and instability at terminal joints, which are exacerbated by the use of fiber lasers with low laser reflectance materials like copper.
Innovation Solution
The use of a fiber laser with high energy density to form a melted portion between the circuit surface and external terminal, or between the metal plate and external terminal, with a gap of 20 μm or less, ensuring stable bonding by creating a conductive material sandwiched between these components, made of copper or copper alloy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If fiber laser bonding is used for terminal bonding in copper-based semiconductor devices, then bonding speed and productivity are improved, but bonding strength varies significantly and reliability deteriorates
Solution Approach 1:
A flux material is introduced as an intermediary substance between the terminal and the copper circuit surface. The flux material facilitates stable laser bonding by mediating the interaction between the fiber laser and the copper surface, reducing reflectance variations and ensuring consistent bonding strength across different bonding positions.
Solution Approach 2:
The bonding process parameters are optimized by controlling the laser power, bonding time, and flux material composition. These parameter changes enable stable bonding strength despite the inherent variability of fiber laser bonding on copper surfaces, resolving the reliability issue while maintaining high productivity.
2Ease of manufacture
If larger gap is allowed between circuit surface and external terminal, then manufacturing ease is improved, but bonding strength decreases and reliability worsens
Solution Approach 1:
The flux material serves as a mediator that fills the gap between the terminal and circuit surface, enabling reliable bonding even with larger gaps. This intermediary substance allows manufacturing with relaxed tolerances while maintaining bonding strength through chemical bonding assistance.
3Quantity of substance
If copper or copper alloy is used for circuit surface and external terminal, then electrical conductivity is improved, but laser reflectance increases and bonding stability deteriorates
Solution Approach 1:
The flux material is introduced as an intermediary that enables stable laser bonding on copper surfaces. It addresses the high reflectance issue by facilitating energy absorption and transfer, allowing copper's superior electrical conductivity to be utilized without compromising bonding stability.
Solution Approach 2:
The bonding process parameters are specifically optimized for copper materials, including laser power settings and flux material composition tailored to copper's thermal and optical properties. This enables stable bonding on high-conductivity copper surfaces.
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 the reliability and longevity of semiconductor devices by stabilizing bonding strength, reducing thermal stress, and maintaining insulating properties, while allowing for downsizing and improved productivity.
Implementation Method 1
irradiating an upper surface of the external terminal with a fiber laser to bond a lower surface of the external terminal to the upper surface of the circuit surface
Implementation Method 2
forming a melted portion of the circuit surface and the external terminal
Implementation Method 3
The circuit surface and the external terminal are each made of copper or copper alloy
Data Source
AI summary
There is provided a semiconductor device including an insulating substrate provided with a circuit surface, and an external terminal bonded to the circuit surface. The circuit surface has an upper surface that is in contact with and bonded to a part of a lower surface of the external terminal. In at least a part of a portion where the upper surface of the circuit surface and the lower surface of the external terminal are in contact with each other, a melted portion of the circuit surface and the external terminal is formed. A gap between the upper surface of the circuit surface and the lower surface of the external terminal has a size of 20 μm or less. The circuit surface and the external terminal are each made of copper or copper alloy.