Sintered Backside Shim for Uniform IGBT Turn-Off
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Solution Overview
Problem
High power semiconductor device press pack modules face challenges in maintaining uniform gate drive signal propagation and avoiding negative gate voltage feedback due to induced voltages across emitter power connection self-inductances, especially under high speed and high current turn-off conditions, which can cause some IGBTs to turn off before others, leading to potential failure.
Innovation Solution
The implementation of a branched balanced impedance network for the auxiliary emitter terminal, which is connected in parallel to the emitter pad of each IGBT die, and the use of a sintered metal assembly bonded to the backside of the semiconductor device die for improved thermal contact, allowing for uniform gate drive signal propagation and immune to electrostatic and electromagnetic fields.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional press pack module design is used with traditional bonding methods, then manufacturing simplicity is maintained, but thermal contact uniformity and gate drive signal propagation uniformity deteriorate
Solution Approach 1:
The patent changes the bonding method from conventional wire bonding or tab bonding to sintering technology. This parameter change in the bonding process enables direct metal-to-metal contact between the copper shim and the emitter pad, achieving uniform thermal and electrical contact without the complexity of traditional multi-step bonding processes. The sintering process creates intimate contact at the microscopic level, ensuring uniform gate drive signal propagation across all IGBTs.
Solution Approach 2:
The patent replaces the mechanical bonding processes (wire bonding, tab welding) with a thermal field-based sintering process. This substitution eliminates the mechanical complexity of bonding equipment and procedures while achieving superior contact uniformity. The sintering process uses controlled thermal and pressure fields to create direct metal contact, improving reliability without proportionally increasing device complexity.
2Productivity
If high current turn-off speed is increased, then power processing capability is improved, but electromagnetic interference and negative gate voltage feedback worsen
Solution Approach 1:
The patent implements equipotentiality by creating uniform electrical potential distribution across all IGBT emitter pads through the sintered copper shim assembly. The low-inductance, high-conductivity copper shims bonded via sintering ensure that all emitters experience the same potential during high-speed turn-off, preventing negative gate voltage feedback and electromagnetic interference that would otherwise cause uneven turn-off behavior.
Solution Approach 2:
The patent segments the electrical connection path into multiple low-inductance copper shim layers, each sintered directly to the IGBT emitter pad and to adjacent shims. This segmentation creates multiple parallel current paths that distribute the high di/dt current evenly, reducing electromagnetic interference and preventing the concentration of stress that would cause uneven turn-off.
3Temperature
If sintered metal assembly is used for thermal contact, then thermal contact uniformity is improved, but manufacturing process complexity increases
Solution Approach 1:
The sintered copper shim assembly serves multiple functions simultaneously: it provides thermal contact, electrical connection, and mechanical support for the IGBT die. This multi-functionality eliminates the need for separate thermal management and electrical connection components, achieving uniform thermal contact without proportionally increasing manufacturing complexity. The same sintering process that creates thermal contact also establishes electrical connectivity.
4Reliability
If uniform gate drive signal propagation is achieved through improved thermal contact, then IGBT turn-off uniformity is improved, but device complexity and assembly steps increase
Solution Approach 1:
The patent merges the thermal management function and electrical connection function into a single sintered copper shim assembly. By combining these functions, the design achieves uniform gate drive signal propagation and uniform IGBT turn-off without the need for separate thermal management components and their associated assembly steps, thereby limiting the increase in device 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
The solution ensures uniform turn-off of IGBTs by providing a highly uniform gate drive signal propagation delay and high immunity to electromagnetic interference, preventing over-stressing and failure of IGBTs during high current operations.
Implementation Method 1
a sintered metal assembly bonded to the backside of the semiconductor device die
Data Source
AI summary
Within a cassette of a press pack module, a conductive shim is bonded to the backside of a device die by a layer of sintered metal. The die, sintered metal, and shim together form a sintered assembly. The cassette is compressed between a metal top plate member and a metal bottom plate member such that the backside of the assembly is pressed against the top plate member, and such that the frontside of the assembly is pressed against another shim. A central portion of the frontside surface of the die is contacted on the bottom by the other shim, but there is no shim contacting a peripheral portion of the frontside surface. Despite there being no shim in contact with the peripheral portion of the frontside surface, the peripheral portion is in good thermal contact with the top plate member through the sintered metal and the bonded conductive shim.