Ultrasonic Bonding of Hardened Copper Terminals to Substrates
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Large-scale high-capacity semiconductor devices face reliability issues due to stress from heat deformation and misalignment in bonding portions, leading to reduced strength and long-term reliability, especially when using solder bonding or low-hardness external connection terminals.
Innovation Solution
A semiconductor device with external connection terminals made of copper, hardened to at least 90 Vickers hardness, bonded to circuit patterns via ultrasonic welding, where the central bonding end portion is bonded first, followed by alternating bonding of other end portions to increase strength and reduce misalignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If solder bonding is used to bond external connection terminals to circuit patterns, then the bonding process is simple and can be performed at lower cost, but the reliability of bonding portions deteriorates due to heat deformation and stress in large-scale high-capacity semiconductor devices
Solution Approach 1:
The patent replaces thermal bonding (soldering) with mechanical bonding (ultrasonic welding). Ultrasonic welding uses mechanical vibration and pressure to bond copper external connection terminals to copper circuit patterns without melting solder, thereby avoiding heat-induced deformation of the base plate and improving bonding reliability in large-scale high-capacity semiconductor devices
Solution Approach 2:
The patent changes the bonding parameters from thermal (solder melting temperature) to mechanical (ultrasonic vibration frequency and pressure). By controlling ultrasonic vibration parameters and bonding pressure, reliable bonding is achieved without the harmful thermal effects that cause base plate deformation and bonding portion stress
2Power
If external connection terminals are thickened to increase capacity, then the current capacity increases, but the strength and long-term reliability deteriorate when using low-hardness materials
Solution Approach 1:
The patent applies local quality by making the bonding end portions of external connection terminals have different hardness (at least 90 HV) from the main body. This is achieved through selective heat treatment or material composition adjustment at the bonding portions, providing both the required electrical conductivity for high current capacity and the necessary hardness for strength and bonding reliability
Solution Approach 2:
The patent uses composite material structure where the external connection terminal consists of a soft main body (for electrical conductivity and current capacity) and hard bonding end portions (for strength and bonding reliability). This composite structure combines the advantages of both soft and hard materials to satisfy multiple requirements simultaneously
3Productivity
If the semiconductor device is made larger in scale and higher in capacity, then the number of semiconductor devices per unit power is reduced, but the stress on bonding portions increases due to base plate deformation from heat
Solution Approach 1:
The patent replaces thermal bonding with mechanical ultrasonic welding to eliminate the heating process that causes base plate deformation. By using mechanical vibration and pressure for bonding, the system avoids thermal expansion and deformation issues that become critical in large-scale high-capacity semiconductor devices, thereby maintaining bonding reliability while achieving high power conversion efficiency
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
The increased hardness and bonding method enhance the semiconductor device's strength and reliability, reducing misalignment and maintaining high bonding strength, thus improving long-term reliability.
Implementation Method 1
The ultrasonic welding is performed by applying horizontal ultrasonic vibration to a bonding end portion of each external connection terminal while applying a vertical load to a bonding interface between the external connection terminal and the circuit pattern
Data Source
AI summary
An ultrasonic welding tool is used to bond end portions of an external connection terminal to circuit patterns of an insulating substrate, with a Vickers hardness not lower than 90. Bonding end portions are provided integrally with a bar in the external connection terminal. A bonding end portion located substantially in the lengthwise center of the bar is bonded first, then others are bonded alternately in order toward either end. Hardness of the bonding end portions is increased so that strength of the ultrasonic welding portions is increased, and displacement of the bonding end portion in either end from its regular position is suppressed to keep bonding strength high. Bonding strength of the ultrasonic welding portions between the external connection terminal and the circuit patterns of the insulating substrate can be increased so that long-term reliability can be secured in a semiconductor device.