Segmented Leadframe Asymmetry for Flip Chip Die Tilt
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Solution Overview
Problem
In flip chip die attachment, the uneven distribution of pressure due to a gap between the source and gate pads leads to systematic die tilt and low bond layer thickness, causing potential solder joint fractures, which cannot be fully resolved by increasing solder material.
Innovation Solution
A leadframe design with a rectangular area segmented into individual pads, where the first pad is larger than the second and third pads, and the second pad is located in one corner and the third pad in the diagonally opposite corner, with a gap and recess between them, ensuring a symmetric pressure distribution and improved void escape during solder attachment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If more solder material is used to increase bond layer thickness, then bond layer thickness is improved, but die tilt issue is not resolved and device complexity increases
Solution Approach 1:
The patent applies asymmetry by making the first pad larger than the second and third pads. This asymmetric pad configuration compensates for the systematic die tilt caused by the gap between source and gate pads, creating a symmetric pressure distribution during flip chip attachment without requiring additional solder material.
2Reliability
If a gap exists between source pad and gate pad, then electrical connection is achieved, but non-symmetric pressure distribution occurs leading to die tilt
Solution Approach 1:
The asymmetric pad design with the first pad being larger creates a compensating effect that balances the pressure distribution despite the gap between source and gate pads, eliminating die tilt while maintaining electrical connectivity.
Solution Approach 2:
The patent applies local quality by differentiating the pad sizes - the first pad is specifically made larger than the second and third pads. This localized structural variation addresses the pressure distribution issue at the critical pad region without affecting the overall device structure.
3Stability of the object's composition
If symmetric pad configuration is used, then pressure distribution is uniform, but gap between source and gate pads cannot be accommodated
Solution Approach 1:
The patent resolves this contradiction by introducing a controlled asymmetry in pad sizes. The first pad is larger to compensate for the gap effect, creating an asymmetric configuration that achieves symmetric pressure distribution during attachment, thus solving both requirements simultaneously.
Data Source
AI summary
A leadframe for flip chip attaching a semiconductor die thereon includes a rectangular area segmented into individual pads, the individual pads including a first pad, a second pad, and a third pad, wherein the first pad is larger than the second pad and larger than the third pad, and the second pad is located in a first corner area of the rectangular area and the third pad is located in a second corner area of the rectangular area, the second corner area being located diagonally opposite to the first corner area.