Segmented Contact Pad Reducing Peak Current Density in Solder Bumps
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Solution Overview
Problem
Conventional C4 solder bump contact designs face limitations in electromigration performance due to high current density, leading to void formation and failure, especially in lead-free structures where current crowding occurs at the interface between the solder bump and the ball limiting metallization layer.
Innovation Solution
The method involves forming a contact pad in the last wiring level with multiple wires extending from its side edges to vias, each with substantially the same electrical resistance, and using a dielectric capping layer with blocks to divert current and reduce peak current density, along with copper structures to spread current uniformly across the contact pad and solder bump.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single large contact area is used between the pad and BLM layer, then the electrical connection is simplified, but the current density becomes concentrated and electromigration damage increases
Solution Approach 1:
The single large contact area is segmented into multiple smaller contact regions distributed across the pad. This segmentation distributes the current flow paths, reducing peak current density at any single location and thereby improving electromigration resistance while maintaining electrical connectivity.
Solution Approach 2:
Different regions of the contact structure are given different properties - the contact areas are strategically positioned and sized to optimize current distribution. The BLM layer contacts are distributed rather than concentrated, creating local variations in current density that prevent harmful accumulation at single points.
2Area of stationary object
If feature dimensions are shrunk to create smaller devices, then the device size is reduced, but the maximum allowable current density decreases due to electromigration effects
Solution Approach 1:
The contact structure is divided into multiple segments that collectively handle the current load. Even as overall device area shrinks, the segmented approach ensures current is distributed across multiple pathways, maintaining higher current density tolerance in smaller form factors.
Solution Approach 2:
The contact areas are distributed in two-dimensional space across the pad rather than concentrated in one location. This spatial distribution across multiple dimensions allows smaller devices to maintain adequate current handling capacity by utilizing the available area more efficiently.
3Device complexity
If current flows through a narrow region at the leading edge of the via, then the via structure is simplified, but current crowding occurs and electromigration void formation increases
Solution Approach 1:
The via structure is segmented into multiple parallel via paths rather than a single narrow via. This segmentation distributes current flow across multiple channels, eliminating current crowding at the leading edge and preventing void formation while maintaining structural simplicity.
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 approach reduces electromigration damage by distributing current evenly, minimizing peak current density and stress on underlying layers, thereby enhancing the reliability and longevity of semiconductor devices.
Implementation Method 1
Each one of the plurality of wires has substantially the same electrical resistance
Implementation Method 2
electromigration damage by distributing current evenly, minimizing peak current density
Data Source
AI summary
Structures and methods to reduce maximum current density in a solder ball are disclosed. A method includes forming a contact pad in a last wiring level and forming a plurality of wires of the contact pad extending from side edges of the contact pad to respective ones of a plurality of vias. Each one of the plurality of wires has substantially the same electrical resistance.