QFN Leadframe Recess Structure for Taller Wettable Flanks
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Solution Overview
Problem
Current semiconductor device packages, particularly Quad-Flat No-Leads (QFN) packages, face limitations in wettable flank height and are prone to failures due to defects in wire/ribbon bonding, leading to issues like weld off/weld lift, which affect the reliability of automotive products.
Innovation Solution
A leadframe design with recessed portions and a modified wire bonding scheme that increases wettable flank height and provides an additional electrical path between the wire/ribbon and solder joint, ensuring device reliability through enhanced visibility for inspection and potential for continued operation in case of bond failure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If half-etched tie bars are provided during packaging to keep leads in place, then leads are kept in place, but wettable flank height is limited to half the leadframe thickness
Solution Approach 1:
The leadframe is divided into functional segments: leads with recessed portions for wire bonding, tie bars for mechanical support, and wettable flanks for soldering. This segmentation allows each component to perform its specific function optimally without compromising others.
Solution Approach 2:
The invention introduces a vertical dimension by creating recessed portions in the leads that extend downward from the top surface. This allows wire/ribbon to be bonded in the recessed area, enabling the wettable flank to extend higher without compromising lead stability, as the wire bond is secured within the recessed volume rather than relying solely on surface-level tie bars.
2Reliability
If wire/ribbon bonding is used to form electrical connections, then electrical connections are established, but defects in bonding may result in failure of the whole unit
Solution Approach 1:
The recessed portions in the leads serve as pre-prepared bonding chambers that cushion and protect the wire/ribbon bonding process. The recessed geometry provides mechanical support and containment for the bonded wire, reducing the risk of bonding defects and providing a margin of error that enhances overall connection reliability.
Solution Approach 2:
The recessed portion acts as an intermediary structure between the wire/ribbon and the lead body. It provides a dedicated bonding zone that mediates the connection process, allowing for more reliable bonding while simplifying the overall process by containing all bonding activities within this defined recessed space.
3Measurement precision
If wettable flanks are made taller for better inspection visibility, then inspection capability is improved, but leadframe structure becomes more complex
Solution Approach 1:
The leadframe structure implements local quality by creating recessed portions only in specific locations where wire bonding is required, rather than uniformly modifying the entire leadframe. This localized modification allows wettable flanks to be taller for better inspection visibility while maintaining simple structures in non-critical areas.
Solution Approach 2:
The recessed portions are nested within the lead structure, creating a hierarchical geometry where the wire bonding area is contained within the lead body. This nesting allows the wettable flank to extend outward and upward for inspection visibility while the recessed bonding area provides the necessary structural complexity only where required.
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 increases the reliability of semiconductor device packages by allowing for increased wettable flank height and direct electrical paths, facilitating automatic inspection and ensuring device functionality even in case of bond detachment, thus improving the overall reliability of automotive products.
Implementation Method 1
a wire bonding scheme wherein the wire/ribbon is bonded to a lead in the recessed portion
Implementation Method 2
facilitating automatic inspection and ensuring device functionality even in case of bond detachment
Data Source
AI summary
A semiconductor die is arranged on a first surface of a leadframe having a first thickness between the first surface and a second surface opposite the first surface and an array of electrically conductive leads. Terminal recesses are provided in the electrically conductive leads in the array at the first surface. At the terminal recesses, the electrically conductive leads have a second thickness less than the first thickness. The semiconductor die is coupled with the electrically conductive leads via wires or ribbons having ends coupled to the electrically conductive leads arranged in the terminal recesses. The leadframe is partially cut starting from the second surface at the terminal recesses with a cutting depth between the first thickness and the second thickness. The partial cut produces exposed surfaces of the electrically conductive leads and the ends of the electrically conductive elongated formations providing wettable flanks for solder material.