FLI Corner Guard Structure for Uniform Electroplated Bump Height
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Solution Overview
Problem
The non-uniform electro-deposition of metal ions in the first level interconnect (FLI) layer of electronic packages results in significant variations in bump thickness, leading to assembly issues and high yield losses, particularly as the pitch decreases, causing large average bump thickness variation (rBTV) and non-uniform current density across the FLI bump region.
Innovation Solution
Incorporating guard features with increased metal density adjacent to the FLI bump region to normalize current density, these features are plated in parallel with the bumps but are not electrically coupled to the circuitry, mitigating the bump height variations by reducing current density spikes at edges and corners.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If electroplating is performed on the FLI bump region without guard features, then the plating process is simple and fast, but the bump thickness varies significantly between edge bumps and interior bumps
Solution Approach 1:
Guard features are introduced as intermediary elements surrounding the FLI bump region. These guard features act as a mediator that redistributes current density during electroplating, preventing excessive current concentration at edge bumps and corners. The guard features are plated simultaneously with the bumps but are electrically isolated, serving purely as current distribution structures that enable uniform bump thickness without requiring post-plating adjustments.
Solution Approach 2:
The invention changes the local metal density parameter by introducing guard features with higher metal density around the perimeter of the bump region. This parameter change modifies the current density distribution during electroplating, creating a more uniform plating environment. The guard features effectively transform the boundary conditions of the electroplating process, allowing edge and corner bumps to receive appropriate current density similar to interior bumps.
2Quantity of substance
If the pitch of FLI bumps is decreased to increase density, then more bumps can be accommodated, but the rBTV specification becomes more difficult to meet
Solution Approach 1:
By introducing guard features, the invention changes the current density distribution parameter across the bump region. This allows the system to accommodate higher bump densities (smaller pitches) while maintaining uniform thickness control. The guard features scale with the bump pitch, ensuring that even as bumps become smaller and more numerous, the current distribution remains optimized for uniform plating.
Solution Approach 2:
The guard features perform preliminary anti-action by preemptively addressing the current density concentration problem before electroplating occurs. By pre-positioning these high-density metal structures around the bump region, the system prevents the formation of non-uniform current distribution that would otherwise occur with decreased pitch, thereby maintaining manufacturing precision even as bump density increases.
3Manufacturing precision
If guard features are added to normalize current density, then bump thickness uniformity improves, but the manufacturing process becomes more complex
Solution Approach 1:
The manufacturing process merges the formation of guard features and bumps into a single electroplating step. Both structures are plated simultaneously from the same plating solution, using the same process parameters. The guard features and bumps share the same process flow, requiring only one plating bath, one set of process controls, and one inspection cycle, thereby minimizing the increase in manufacturing complexity while achieving improved rBTV control.
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 guard features effectively reduce bump height variations, achieving a low rBTV of approximately 10 μm or less, thereby improving assembly yields and maintaining uniformity across the FLI bump region, even as pitches decrease.
Implementation Method 1
Sharp changes in local metal density within the first level interconnect layer (FLI) leads to non-uniform electro-deposition of incoming metal ions within each unit
Data Source
AI summary
Embodiments disclosed herein include electronic packages and methods of forming such packages. In an embodiment an electronic package comprises a package substrate, and a first level interconnect (FLI) bump region on the package substrate. In an embodiment, the FLI bump region comprises a plurality of pads, and a plurality of bumps, where each bump is over a different one of the plurality of pads. In an embodiment, the electronic package further comprises a guard feature adjacent to the FLI bump region. In an embodiment, the guard feature comprises, a guard pad, and a guard bump over the guard pad, wherein the guard feature is electrically isolated from circuitry of the electronic package.