Brown-Oxide Layer on Bonding Pads Prevents Flip Chip Bump Toppling
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Solution Overview
Problem
Conventional flip chip interconnect technologies face challenges with reduced pitch between circuit carriers and dies due to bump toppling and manufacturing issues related to solder mask tolerance and shifting.
Innovation Solution
A circuit carrier with a brown-oxide layer on bonding pads allows direct bump placement on the oxide layer, increasing pitch and eliminating the need for a solder mask, thereby simplifying the manufacturing process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional flip chip interconnect technology is used with solder masks, then bonding pads can be protected, but the pitch between circuit carrier and die is reduced due to bump toppling
Solution Approach 1:
The patent changes the surface property of the bonding pad from a solder mask-covered copper surface to a brown-oxide layer surface. This parameter change in surface chemistry and morphology prevents bump toppling during reflow, maintaining adequate pitch between carrier and die while ensuring reliable bonding.
Solution Approach 2:
The patent eliminates the solder mask layer, removing a complex manufacturing step and material. The brown-oxide layer serves as both the bonding surface and protective layer, simplifying the structure while achieving the same functional goals with fewer components.
2Manufacturing precision
If solder mask is used to cover bonding pads, then manufacturing precision can be maintained, but process tolerance and shifting occur during solder mask manufacture
Solution Approach 1:
The patent extracts and removes the solder mask layer from the bonding pad structure. By eliminating this layer, the patent removes the source of process tolerance and shifting issues, simplifying the manufacturing process while maintaining precise alignment through the brown-oxide layer formation.
Solution Approach 2:
The patent segments the bonding pad functionality into distinct layers: the copper conductive layer for electrical connection and the brown-oxide layer for bonding and protection. This segmentation allows each layer to be optimized for its specific function without the compromises required by a unified solder mask approach.
3Reliability
If bumps are bonded directly to copper bonding pads, then electrical connection is achieved, but bumps topple and enclose bonding pads entirely
Solution Approach 1:
The patent introduces the brown-oxide layer as an intermediary between the copper bonding pad and the bump. This intermediate layer modifies the bonding characteristics, preventing bump toppling while maintaining electrical connection, thus resolving the shape distortion issue without sacrificing electrical reliability.
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 brown-oxide layer on bonding pads prevents bump toppling and reduces manufacturing complexities by allowing easier alignment and connection, enhancing the reliability and efficiency of the flip chip interconnect process.
Implementation Method 1
a surface of the bonding pad has a brown-oxide layer
Data Source
AI summary
A circuit carrier suitable for being connected with a bump is provided. The circuit carrier includes a substrate and at least one bonding pad. The substrate has a bonding pad disposed on a surface thereof for being connected with the bump. A brown-oxide layer is disposed on a surface of the bonding pad.