FLI Bump Plating With Selective Undercut for Fine-Pitch Anchoring
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Solution Overview
Problem
Fine pitch interconnects in electronic packages lack mechanical anchoring, leading to susceptibility to delamination and galvanic corrosion, which limits design flexibility and reliability.
Innovation Solution
Incorporating an anchoring undercut in the interconnects, lined with a seed layer using a conformal deposition process, to provide mechanical anchoring and protect surface finishes from corrosion, allowing for flexible design without sacrificial layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If fine pitch interconnects are used in embedded bridge architectures, then design density and integration are improved, but mechanical anchoring is lost making them susceptible to delamination
Solution Approach 1:
The interconnect structure is segmented into multiple functional zones: the bridge region with undercut for anchoring, the pad region for electrical connection, and the solder resist region for protection. This segmentation allows each region to be optimized independently - the bridge area gets mechanical anchoring through undercut while maintaining fine pitch density, and the pad area maintains electrical connectivity.
Solution Approach 2:
The solution transitions from a two-dimensional planar interconnect to a three-dimensional structure by creating undercut features that extend vertically and laterally beneath the solder resist. This dimensional change provides mechanical anchoring volume without increasing the planar footprint, thus maintaining fine pitch density while adding reliability.
2Ease of manufacture
If conventional plating processes are used without protective layers, then manufacturing simplicity is improved, but galvanic corrosion occurs between gold and copper
Solution Approach 1:
Protective measures are applied locally only where needed - the undercut regions and areas adjacent to gold finishes receive conformal coating of the seed layer, while other areas maintain their original structure. This localized approach prevents galvanic corrosion at critical interfaces without adding global process complexity.
Solution Approach 2:
The conformal seed layer acts as an intermediary barrier between dissimilar metals (gold and copper) that would otherwise create galvanic corrosion cells. This thin intermediate layer electrically isolates the two metals while maintaining manufacturing simplicity by using the existing seed layer material already required for plating.
3Reliability
If sacrificial layers are added to prevent corrosion, then protection from galvanic corrosion is improved, but device complexity increases
Solution Approach 1:
The conformal seed layer serves multiple functions simultaneously: it provides the necessary conductive base for electrolytic plating, acts as a protective barrier against galvanic corrosion, and creates mechanical anchoring through the undercut geometry. This multi-functionality eliminates the need for separate sacrificial layers, maintaining reliability while reducing device complexity.
Solution Approach 2:
The protective corrosion prevention function is merged with the existing seed layer that is already required for the plating process. Instead of adding a separate protective layer, the seed layer is conformally deposited to cover both the pad and undercut regions, combining structural, electrical, and protective functions in a single layer.
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 anchoring undercut enhances the reliability of fine pitch interconnects by preventing delamination and reducing galvanic corrosion, thereby improving the overall reliability and design flexibility of electronic packages.
Implementation Method 1
the conformal deposition of a seed layer over the pad and the undercut
Implementation Method 2
the electrolytic plating of a bump in the opening
Data Source
AI summary
Embodiments disclosed herein include an electronic package. In an embodiment, the electronic package comprises a substrate and a pad on the substrate. In an embodiment, a layer is over the pad and the substrate, and an opening through the layer is above the pad. In an embodiment, sidewalls of the layer define the opening. In an embodiment, an undercut at an end of the opening adjacent to the pad is provided, where the undercut is positioned between the pad and the layer. In an embodiment, a bump is in the opening, where the bump at least partially fills the undercut