Leadframe Tie Bar Structure for Moisture-Resistant Singulation
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Solution Overview
Problem
Delamination at the interface between package materials in semiconductor devices, often caused by moisture infiltration through tie bars during the singulation process, poses a reliability issue, as it can lead to device failure.
Innovation Solution
A meander-like or serpentine structure is formed in the tie bars by half-etching from both sides of the leadframe, creating a longer, tortuous path for moisture to reach the die area, and additional dummy pads are created to enhance the thermo-mechanical robustness of solder joints.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If straight tie bars are used during singulation, then manufacturing process is simple, but moisture penetration path is direct causing delamination
Solution Approach 1:
The tie bar is designed with a meander-like (curved, non-linear) shape instead of a straight configuration. This curved path increases the distance moisture must travel to reach the die area, effectively reducing moisture penetration risk while maintaining manufacturing simplicity through standard etching processes
2Reliability
If meander-like tie bar structure is formed by half-etching from both sides, then moisture penetration path is lengthened improving reliability, but manufacturing process complexity increases
Solution Approach 1:
The meander-like structure is achieved through half-etching from both sides of the leadframe, creating a curved tie bar path that lengthens the moisture penetration distance. The etching process forms the serpentine pattern by removing material alternately from both surfaces, achieving the curved geometry without requiring complex multi-step manufacturing procedures
Solution Approach 2:
The tie bar structure utilizes the third dimension by etching from both the top and bottom surfaces of the leadframe. This bidirectional etching approach creates the meander-like pattern in the vertical dimension, allowing the tie bar to follow a curved path that increases moisture path length while maintaining a planar overall structure
3Productivity
If conventional singulation is performed, then productivity is high, but exposed tie bar remainders create direct moisture paths to die area
Solution Approach 1:
The meander-like tie bar configuration ensures that even when singulated, the exposed remainder follows a curved path rather than a straight line. This curved geometry extends the moisture penetration distance from the package exterior to the die area, reducing the harmful effect of moisture infiltration while maintaining standard singulation productivity
Data Source
Figure 1
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AI summary
An electrically conductive substrate (12) for a plurality of semiconductor devices (10) has mutually opposed first (121) and second (122) surfaces and comprises electrically conductive die pads (12A) configured to have semiconductor chips (14) arranged thereon as well as arrays of electrically conductive leads (12B) arranged around the electrically conductive die pads (12A). The substrate (12) comprises elongated electrically conductive connecting bars (100) connected to the electrically conductive die pads (12A). The elongated connecting bars (100) are configured to be cut (B) at intermediate points (SL) along their length to provide singulated substrate portions and have distributed along their length first recesses (121A) at the first surface (121) alternating with second recesses (122A) (121A, 122A) at the second surface (122). Once cut (B) at the intermediate points (SL), the elongated connecting bars (100) are partitioned into bar remainders (100') extending from a distal end (100A) to an electrically conductive die pad (12A) in a singulated substrate portion. The bar remainders (100') have a serpentine pattern with one or more loops between their distal end (100A) exposed at the surface of the insulating encapsulation (20) of the device package and the electrically conductive die pad (12A), thus creating tortuous paths (WPP') countering moisture penetration into the device package. The elongated connecting bars (100) comprise a sequence of adjacent sections having the first recesses (121A) and the second recesses (122A) etched therein, with these adjacent sections alternately located at the opposed first (121) and second (122) surfaces, wherein dummy pads (120A) left exposed by the encapsulation (20) are formed at the second surface (122).