Multilayer Surface Finish for Microelectronic Interconnection Pads
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Solution Overview
Problem
Current surface finishes for microelectronic interconnection pads fail to meet the increasing current demands of smaller microelectronic components due to limitations in ductility and electro-migration resistance, leading to potential joint failure and reduced maximum current capacity.
Innovation Solution
A multilayer interlayer structure is introduced, comprising a ductile layer, an electro-migration resistant layer, and a barrier layer, which forms a durable and conductive interface between interconnection pads and solder interconnects, enhancing both ductility and electro-migration resistance without increasing brittleness or causing bridging issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single-layer surface finish is used, then the structure is simple and manufacturing is easy, but the electro-migration resistance is insufficient for high current demands
Solution Approach 1:
The surface finish is segmented into multiple functional layers: a first interlayer (e.g., nickel) providing electro-migration resistance, a second interlayer (e.g., gold) providing ductility and solder wetting, and a barrier layer preventing diffusion. Each layer performs a specific function, collectively achieving high electro-migration resistance while maintaining manufacturability through standardized deposition processes.
Solution Approach 2:
The patent employs composite material structure combining different metals with complementary properties. The first interlayer uses high electro-migration resistance materials (nickel, palladium), the second interlayer uses ductile materials (gold, silver), and the barrier layer uses diffusion-blocking materials (ruthenium, rhodium). This composite approach achieves superior overall performance that no single material could provide alone.
2Reliability
If the surface finish is made thicker to improve electro-migration resistance, then current capacity increases, but the joint becomes more brittle and prone to cracking
Solution Approach 1:
Different regions of the surface finish have different thicknesses and material compositions optimized for their specific functions. The first interlayer (electro-migration resistance) is positioned where maximum current flow occurs, the second interlayer (ductility) is optimized at the solder interface, and the barrier layer is strategically placed at diffusion boundaries. This local optimization achieves high electro-migration resistance without compromising overall joint ductility.
Solution Approach 2:
The surface finish is divided into multiple thin functional layers rather than one thick layer. This segmentation allows each layer to be optimized for its specific purpose while maintaining overall flexibility. The cumulative thickness provides electro-migration resistance, but the thin-layered structure prevents brittleness that would result from a single thick layer.
3Reliability
If a multilayer interlayer structure is introduced, then both ductility and electro-migration resistance are enhanced, but the manufacturing process becomes more complex
Solution Approach 1:
The multilayer interlayer structure is formed as an integrated part of the existing surface finish fabrication process, using preliminary deposition steps that are incorporated into the standard manufacturing workflow. The barrier layer is deposited during the same process sequence as the interlayers, eliminating the need for separate fabrication steps and minimizing additional process complexity.
Solution Approach 2:
The multilayer structure serves multiple functions simultaneously: the first interlayer provides electro-migration resistance, the second interlayer provides ductility and solder wetting, and the barrier layer prevents material diffusion. This multi-functionality is achieved within a single integrated fabrication process, making the complex structure manufacturable through standardized semiconductor processing techniques.
4Reliability
If the surface finish is optimized for high current capacity, then electro-migration resistance improves, but the joint becomes less ductile and more prone to failure under thermal stress
Solution Approach 1:
The surface finish uses composite materials with complementary thermal and electrical properties. The first interlayer (nickel, palladium) provides electro-migration resistance for high current capacity, the second interlayer (gold, silver) provides thermal stability and ductility, and the barrier layer (ruthenium, rhodium) prevents thermal degradation and material diffusion. This composite structure achieves both high current capacity and thermal stability that no single material could provide alone.
Solution Approach 2:
The surface finish has locally optimized properties: the first interlayer is positioned where maximum current density occurs to provide electro-migration resistance, the second interlayer is optimized at the solder interface for thermal stress accommodation, and the barrier layer is placed at diffusion boundaries. This local quality optimization ensures both high current capacity and joint stability under thermal stress.
Data Source
AI summary
A surface finish may be formed in a microelectronic structure, wherein the surface finish may include a multilayer interlayer structure. Thus, needed characteristics, such as compliance and electro-migration resistance, of the interlayer structure may be satisfied by different material layers, rather attempting to achieve these characteristics with a single layer. In one embodiment, the multilayer interlayer structure may comprises a two-layer structure, wherein a first layer is formed proximate a solder interconnect and comprises a material which forms a ductile joint with the solder interconnect, and a second layer comprising a material having strong electro-migration resistance formed between the first layer and an interconnection pad. In a further embodiment, third layer may be formed adjacent the interconnection pad comprising a material which forms a ductile joint with the interconnection pad.