Semiconductor Bus Bar Fusing for Crack Resistance
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Solution Overview
Problem
The existing methods for bonding bus bars and connection terminals in semiconductor devices are prone to cracking, which can lead to reduced electrical connectivity due to stress variations during power cycles, and existing welding techniques do not adequately secure the fusing portions between the bus bar and the connection terminal.
Innovation Solution
A semiconductor device design featuring a fusing portion with a jointing portion welded to the bus bar and a non-jointing portion, where the connection terminal includes a taper part and plated layers of nickel and tin for enhanced laser welding, and the fusing portion is positioned off-center to reduce stress concentrations and improve bonding strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If laser welding is used to bond bus bar and connection terminal, then bonding speed and automation are improved, but cracking occurs in the fusing portion due to stress variations during power cycles
Solution Approach 1:
The connection terminal is designed with different structural characteristics in different regions: the upper part has a larger diameter without taper for strong laser welding, while the lower part has a tapered structure with smaller diameter to reduce stress concentration. This local differentiation allows the same component to simultaneously achieve high bonding strength and crack resistance in different zones.
Solution Approach 2:
The connection terminal employs an asymmetric diameter design where the upper portion has a larger diameter than the lower portion. This asymmetric structure creates a stress distribution pattern that reduces peak stress at critical locations while maintaining adequate bonding area, thereby preventing crack propagation during thermal cycling.
2Reliability
If the connection terminal passes through the bus bar opening, then electrical connection is established, but the fusing portion is insufficiently secured leading to potential connection failure
Solution Approach 1:
The connection terminal's diameter is varied along its length, with the upper part having a larger diameter optimized for laser welding fusion and the lower part having a smaller tapered diameter. This parameter change creates optimal conditions for both electrical conductivity and mechanical bonding strength in the fusing portion.
Solution Approach 2:
The tapered lower portion of the connection terminal acts as an intermediary structure that transitions between the larger upper diameter and the bus bar opening. This intermediate geometry distributes stress more evenly and provides adequate fusion area while maintaining electrical continuity.
3Shape
If the fusing portion is positioned centrally, then symmetry is maintained, but stress concentrations occur leading to cracking
Solution Approach 1:
The connection terminal deliberately breaks symmetry by having different diameters at different heights. The upper portion has a larger diameter for welding, while the lower portion tapers to a smaller diameter, creating an asymmetric stress distribution that prevents stress concentration at any single point and reduces crack risk.
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 design enhances the bonding strength and reduces the likelihood of cracking, ensuring stable electrical connectivity and improved reliability of the semiconductor device by distributing stress effectively and securing a sufficient fusion area.
Implementation Method 1
Bonding a bus bar and an external connection terminal of a semiconductor module by laser welding has been known
Implementation Method 2
the connection terminal includes a taper part and plated layers of nickel and tin for enhanced laser welding
Data Source
AI summary
A semiconductor device including a connection terminal that is electrically connected to a semiconductor chip, a bus bar with an opening through which the connection terminal passes, and a fusing portion including a jointing portion, which is provided over an upper surface of the bus bar from an upper part of the connection terminal that is positioned above the upper surface of the bus bar by making the connection terminal pass through the opening of the bus bar, is provided.