Undercut Mechanical Pillars for Semiconductor Stress Protection
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Solution Overview
Problem
Conventional mechanical pillars in semiconductor devices can fail under stress, causing damage to adjacent structures and components, leading to potential device failure.
Innovation Solution
The implementation of weakened mechanical pillars that are designed to fail without damaging adjacent structures, with a configuration that includes undercutting the seed layer to reduce the cross-sectional area and enhance the difference in mechanical strength between mechanical and live pillars, allowing the mechanical pillars to protect the live pillars and provide additional functions like underfill capillary action and thermal transport.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional mechanical pillars are used to provide mechanical support, then structural support is improved, but damage to adjacent structures upon pillar failure increases
Solution Approach 1:
The mechanical pillar is segmented into multiple layers with different material properties. The first layer (at the base) has higher strength to provide mechanical support, while the second layer (at the top) has lower strength to fail first and protect adjacent structures. This segmentation allows the pillar to provide structural support while limiting damage propagation upon failure.
Solution Approach 2:
Different portions of the mechanical pillar are made from materials with different mechanical properties. The base portion uses a stronger material to bear load, while the top portion uses a weaker material that will fail preferentially. This local variation in material quality ensures that failure occurs in a controlled manner that protects sensitive adjacent structures.
2Reliability
If mechanical pillars are made stronger to prevent failure, then reliability is improved, but damage potential upon failure increases
Solution Approach 1:
The mechanical pillar is designed with a predetermined weak point in the form of a second layer with lower strength material. This weak point acts as a cushion that will fail first, absorbing the stress and preventing it from propagating to adjacent passivation materials and live pillars. The design anticipates potential failure and prepares a protective mechanism in advance.
Solution Approach 2:
The potential harmful effect of pillar failure is converted into a beneficial protective mechanism. By designing the pillar to fail in a controlled manner at the second layer, the failure itself becomes a protective action that prevents greater damage to adjacent structures. The weakness is deliberately engineered to serve as a safety feature.
3Ease of manufacture
If uniform pillar structures are used, then manufacturing simplicity is maintained, but differentiation between mechanical and live pillars is reduced
Solution Approach 1:
The mechanical pillars are differentiated from live pillars through local quality variations. Mechanical pillars contain a second layer with lower strength material, while live pillars do not have this weakened layer. This local distinction allows both pillar types to be manufactured using similar processes while ensuring functional differentiation through material composition variations.
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
This design minimizes damage to passivation materials and underlying structures upon mechanical failure, ensuring the integrity of active circuitry and extending the lifespan of semiconductor devices by allowing mechanical pillars to fail before live pillars, while maintaining functionality post-failure.
Implementation Method 1
Mechanical failure of conventional mechanical pillars, however, can cause damage to important components (e.g., functional features, live circuitry, etc.) of a semiconductor device
Implementation Method 2
a configuration that includes undercutting the seed layer to reduce the cross-sectional area and enhance the difference in mechanical strength between mechanical and live pillars
Implementation Method 3
Mechanical pillars, while not providing electrical connection to functional features of the semiconductor die, can provide mechanical support, thermal transfer, and various other functional and structural benefits
Implementation Method 4
allowing the mechanical pillars to protect the live pillars and provide additional functions like underfill capillary action and thermal transport
Data Source
AI summary
A method of manufacturing a semiconductor device having a conductive substrate having a first surface, a second surface opposite the first surface, and a passivation material covering a portion of the first surface can include applying a seed layer of conductive material to the first surface of the conductive substrate and to the passivation material, the seed layer having a first face opposite the conductive substrate. The method can include forming a plurality of pillars comprising layers of first and second materials. The method can include etching the seed layer to undercut the seed layer between the conductive substrate and the first material of at least one of the pillars. In some embodiments, a cross-sectional area of the seed layer in contact with the passivation material between the first material and the conductive substrate is less than the cross-sectional area of the second material.