AlN Substrate Ultrasonic Bonding for Semiconductor Devices
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Solution Overview
Problem
Aluminum nitride (AlN) insulating substrates used in semiconductor devices are prone to cracking during ultrasonic welding, leading to insulation defects and limiting mass production due to their mechanical weakness compared to other ceramic materials like alumina (Al2O3) or silicon nitride (Si3N4).
Innovation Solution
A semiconductor device design featuring a heat-dissipating base with a first conductive layer bonded to an AlN insulating substrate, a second conductive layer bonded to the substrate, and an electrode terminal with a bonding edge that undergoes solid-state flow bonding to the second conductive layer using ultrasonic waves within a temperature range of 50° C. to 125° C., minimizing crystal grain diameter at the bonded interface to less than or equal to 1 μm and maintaining indentations from the ultrasonic horn.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If ultrasonic welding is applied to bond electrode terminals to AlN insulating substrate, then bonding strength is improved, but the insulating substrate is susceptible to cracking leading to insulation defects
Solution Approach 1:
The patent applies parameter changes by controlling the welding temperature to be below the melting point of the molten metal electrode (maintaining it at approximately 50°C to 150°C rather than higher temperatures). This temperature parameter control allows ultrasonic welding to achieve strong bonding while preventing excessive thermal stress that would cause cracking in the AlN insulating substrate, thus resolving the contradiction between bonding strength and insulation reliability
Solution Approach 2:
The patent utilizes periodic action through ultrasonic vibrations during the welding process. The ultrasonic waves provide cyclic mechanical energy that facilitates bonding between the electrode terminal and conductive pattern while the periodic nature of the vibrations prevents continuous thermal stress accumulation, thereby achieving strong bonds without substrate cracking
2Temperature
If AlN insulating substrate is used for its excellent thermal conductivity, then heat dissipation performance is improved, but mechanical strength is reduced making mass production difficult
Solution Approach 1:
The patent changes the welding temperature parameter to a lower range (50°C to 150°C below the melting point of the electrode metal) that is suitable for AlN substrates with lower mechanical strength. This parameter adjustment enables the use of AlN for its superior thermal conductivity while avoiding welding conditions that would cause cracking, thus resolving the contradiction between thermal performance and mechanical strength
Solution Approach 2:
The patent replaces traditional high-temperature mechanical welding methods with ultrasonic welding that operates at lower temperatures. This substitution of the welding mechanism allows AlN substrates to be processed without subjecting them to excessive thermal and mechanical stress, enabling mass production while maintaining both thermal conductivity and mechanical integrity
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 prevents cracking of the AlN insulating substrate and achieves strong bonding between the substrate and electrode terminal, enabling reliable mass production by reducing tensile stress and insulation breakdown during ultrasonic welding.
Implementation Method 1
bonding, in a heated state within a range of 50° C. to 125° C., a portion of the top surface of the second conductive layer to the bottom surface of the bonding edge by causing a solid-state flow via ultrasonic waves
Data Source
AI summary
A semiconductor device includes a heat-dissipating base, a first conductive layer bonded to the top surface of the heat-dissipating base, an AlN insulating substrate bonded to the top surface of the first conductive layer, and an electrode terminal having one edge bending to form a bonding edge whose bottom surface faces the top surface of the second conductive layer and is solid-state bonded to a portion of the top surface of the second conductive layer. The crystal grain diameter at the bonded interface of the second conductive layer and electrode terminal is less than or equal to 1 μm, and indentations from the ultrasonic horn are left in the top surface of the bonding edge.