Leadframe Recess Structure for Full-Height Wettable Flanks
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Solution Overview
Problem
Existing semiconductor device packages face limitations in wettable flank height and reliability due to half-etched tie bars, which restrict the visibility of solder joints during automatic optical inspection, and potential failures from wire/ribbon detachment.
Innovation Solution
A leadframe design with recessed portions and a secondary bond between the wire/ribbon and lead, allowing for increased wettable flank height and an additional electrical path, ensuring reliable solder connections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If half-etched tie bars are provided to keep leads in place, then lead positioning is improved, but wettable flank height is limited to half the leadframe thickness
Solution Approach 1:
The patent removes the half-etched tie bars from the leadframe structure. By extracting this constraint element, the lead positioning function is maintained through alternative means (leadframe geometry and molding process) while eliminating the limitation on wettable flank height, allowing the flanks to extend the full height of the leadframe.
Solution Approach 2:
Instead of using tie bars to hold leads in place (conventional approach), the patent inverts the approach by designing the leadframe and molding process to inherently position leads correctly without requiring intermediate tie bar structures. This inversion removes the height constraint imposed by the tie bar etching depth.
2Reliability
If wire/ribbon bonding is performed to connect semiconductor chip to leads, then electrical connection is improved, but device fails upon wire/ribbon detachment
Solution Approach 1:
The patent creates a recessed portion in the lead at the bonding location before wire/ribbon bonding occurs. This recessed structure acts as a cushioning feature that mechanically secures the wire/ribbon bond, preventing detachment. The recess provides a physical barrier and anchoring point that protects against the harmful effect of wire/ribbon detachment.
Solution Approach 2:
The patent applies local quality by creating a recessed portion only at specific bonding locations on the leads, rather than modifying the entire lead structure. This localized modification provides enhanced mechanical security for wire/ribbon bonds at critical points while maintaining the overall integrity and functionality of the leadframe.
3Measurement precision
If wettable flank height is increased for better inspection visibility, then automatic optical inspection is improved, but leadframe structure becomes more complex
Solution Approach 1:
The patent segments the leadframe manufacturing process into distinct stages: forming recessed portions at bonding locations, bonding wire/ribbon, applying solder, and finally removing tie bars. This segmentation allows each step to be optimized independently, achieving full-height wettable flanks for inspection without requiring complex integrated structures.
Solution Approach 2:
The patent performs preliminary actions by creating recessed portions in leads and positioning wire/ribbon bonds before final soldering and inspection. These preliminary structural preparations enable the achievement of full-height wettable flanks that provide both mechanical security and inspection visibility without adding complexity to the final structure.
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
Enhances the visibility of solder joints for automatic inspection and provides a secondary connection path to maintain device functionality in case of wire/ribbon detachment, improving package reliability.
Implementation Method 1
a metal film is formed on exposed surfaces of the first and second leads by a plating method
Data Source
Figure 1~2
Figure 3~5
Figure 6~8
AI summary
One or more semiconductor dice (14) are arranged on a die pad (12A) at a first surface of a support substrate such as a leadframe (12), the support substrate (12) having a first thickness (T1) between the first surface and a second surface opposite the first surface and comprising an array of electrically conductive leads (12B) around the die pad (12A). Terminal recesses (200) are provided in electrically conductive leads (12B) in the array at the first surface of the support substrate (12). The electrically conductive leads (12B) in the array of electrically conductive leads (12B) have at the terminal recesses (200) a second thickness (T2) less than the first thickness (T1). The semiconductor die (14) is coupled with the electrically conductive leads (12B) via electrically conductive elongated formations such as wires or ribbons (16) having coupling ends (161, 162) to the electrically conductive leads (12B) arranged in the terminal recesses (200). The support substrate (12) is partially cut starting from the second surface at the terminal recesses (200) with a cutting thickness between the first thickness (T1) and the second thickness (T2). The partial cut produces exposed surfaces of the support substrate (1200A) and the coupling ends (1200B) of the electrically conductive elongated formations (16) providing wettable flanks for solder material (SM).