Channel-Shaped Tie Bars for Low-Stress Leadframe Singulation
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Solution Overview
Problem
Current semiconductor device manufacturing processes face issues with mechanical cutting during singulation, which induces stresses that can lead to premature failure due to uniform tie bars, and using thinner tie bars increases the risk of die pad tilt.
Innovation Solution
Implementing tie bars with a channel-shaped (U-shaped) cross-section at their median part, achieved through coining or etching, provides higher stiffness and easier cutting during singulation while reducing stress and tilt risks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If uniform tie bars with constant thickness are used, then the structure is simple to manufacture, but mechanical cutting during singulation induces stresses that lead to leadframe/mold detachment
Solution Approach 1:
The tie bar cross-section is modified locally at the cutting zone to have a channel-shaped (U-shaped) profile, while other portions maintain the original rectangular cross-section. This local modification reduces cutting-induced stresses at the critical cutting location without changing the overall tie bar structure, thus maintaining manufacturing simplicity while improving reliability.
2Ease of operation
If thinner tie bars are used, then cutting during singulation is facilitated and stresses are reduced, but the risk of die pad tilt during assembly increases
Solution Approach 1:
The cross-sectional geometry of the tie bar is changed from a solid rectangular shape to a channel-shaped (U-shaped) profile at the cutting zone. This parameter change reduces the material cross-section area, facilitating easier cutting and reducing cutting-induced stresses, while the channel shape maintains sufficient structural integrity to prevent die pad tilt during assembly.
3Strength
If channel-shaped tie bars are used, then stiffness is increased and die pad support is improved, but the tie bar structure becomes more complex
Solution Approach 1:
The channel-shaped cross-section is applied only locally at the median part of the tie bar where cutting occurs, rather than throughout the entire tie bar length. This local application increases stiffness and moment of inertia at the critical cutting zone to prevent die pad tilt, while minimizing the overall structural complexity and maintaining ease of manufacture.
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 channel-shaped tie bars offer improved support for die pads, reducing the risk of tilt and bending while facilitating easier cutting, thereby enhancing the reliability and stability of semiconductor devices during the singulation process.
Implementation Method 1
Such a channel or (inverted) U shape can be bestowed on the tie bars done during leadframe manufacturing using a coining or etching process, for instance.
Data Source
AI summary
A semiconductor die mounting substrate, such as a pre-molded leadframe, is provided with die pads, wherein each die pad has opposed first and second surfaces as well as tie bars projecting therefrom. Semiconductor dice are mounted at the first surface of the die pads. A molding encapsulation material surrounds the semiconductor dice mounted at the first surface of the die pads to produce semiconductor devices, with the semiconductor devices being mutually coupled via the tie bars. The tie bars are then cut transverse to their longitudinal direction at an intermediate singulation location to singulate the semiconductor devices into individual semiconductor devices. The tie bars have a hollowed-out portion with a channel-shaped cross-sectional profile at the intermediate singulation location. Easier-to-cut tie bars can be provided without impairing their stiffness in comparison with tie bars having full rectangular/square cross-sectional shapes.