Leadframe Stress Relief Slot for IC Package Corner Crack Prevention
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Solution Overview
Problem
There is a need for an integrated circuit packaging system that increases density without sacrificing reliability, yield, and high volume manufacturing processes, while reducing costs and improving performance, as existing methods face physical limits and cost factors in scaling down semiconductor devices.
Innovation Solution
The system employs a leadframe strip with a stress relief slot at the frame corner, spanning adjacent sides of the leadframe unit, which includes a paddle, a tie bar, and a lead finger, connected to an integrated circuit and encapsulated to prevent micro-cracks at the package corner, ensuring reliability through stress relief and efficient manufacturing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If multiple semiconductor devices are stacked to increase density, then device density increases, but manufacturing complexity and process difficulty increase
Solution Approach 1:
The leadframe is segmented into modular units with standardized components (paddle, tie bar, lead fingers) that can be repeatedly assembled. The stress relief slot divides the leadframe structure into distinct regions, allowing independent optimization of each segment while maintaining overall integration.
Solution Approach 2:
Multiple leadframe units are nested within a continuous strip structure, allowing multiple devices to be packaged in sequence. The strip configuration enables nested arrangement of multiple semiconductor devices along the length of the leadframe, increasing density without proportionally increasing manufacturing complexity.
2Quantity of substance
If leadframe corners are designed with tight geometry to maximize package size, then package density increases, but micro-cracks form at the corners reducing reliability
Solution Approach 1:
The stress relief slot is positioned at the leadframe corner before the molding process to preemptively address stress concentration issues. This pre-configured feature cushions against molding stresses and thermal expansion forces that would otherwise cause micro-cracks, ensuring reliability is built into the structure before assembly.
Solution Approach 2:
The design accepts that corner regions are naturally prone to stress concentration, but converts this potential harm into a benefit by intentionally placing the stress relief slot at the corner. The slot transforms the harmful stress concentration into a controlled stress distribution pattern that prevents cracking while maintaining overall structural integrity.
3Reliability
If the stress relief slot is positioned to maximize stress relief at the corner, then reliability improves, but the slot may interfere with leadframe unit geometry
Solution Approach 1:
The stress relief slot is localized specifically to the corner region where stress concentration occurs, rather than extending throughout the entire leadframe. This localized approach provides targeted stress relief at the critical corner area while preserving the geometric precision and structural integrity of the main leadframe body and lead fingers.
Solution Approach 2:
The stress relief slot extends slightly beyond the minimum required length to ensure adequate stress relief coverage. By providing partial excess length in the slot, the design ensures sufficient stress distribution while maintaining compatibility with standard leadframe unit dimensions and manufacturing tolerances.
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 stress relief slots effectively dissipate external stress, eliminating micro-cracks and improving reliability by preventing delamination, thus enhancing the packaging system's performance and cost-effectiveness.
Implementation Method 1
The stress relief slot is at a frame corner of the leadframe strip system and spans adjacent sides of the leadframe unit
Data Source
AI summary
A method of manufacture of an integrated circuit packaging system includes: providing a leadframe strip system, having a stress relief slot and a leadframe unit, the stress relief slot is at a frame corner of the leadframe strip system and spans adjacent sides of the leadframe unit, the leadframe unit includes a paddle, a tie bar therefrom, and a lead finger; connecting an integrated circuit and the lead finger; forming an encapsulation covering the integrated circuit; and singulating the integrated circuit in the encapsulation from the leadframe strip system with a package corner of the encapsulation free of micro-cracks with an inspection of the package corner at least 50× view.