IGEPIG Surface Finish for Embedded Die Solder Joint Reliability
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Solution Overview
Problem
Embedding circuit components within package substrates is challenging due to thickness mismatches leading to tilting or shifting, and existing surface finishes like ENEPIG and PdAu plating face issues such as copper diffusion, brittle inter-metallic compound formation, and bath life concerns, affecting solder joint reliability and maximum current limits.
Innovation Solution
Implementing electroless nickel-electroless palladium-immersion gold (ENEPIG) or immersion gold-electroless palladium-immersion gold (IGEPIG) surface finishes, optionally with additional layers of indium or cobalt-iron, to address solder joint reliability and maximum current limitations, while reducing the need for additional lithography steps and ensuring uniform coverage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If ENEPIG surface finish is used, then solder joint reliability is improved, but copper diffusion and brittle inter-metallic compound formation occur
Solution Approach 1:
The patent introduces an intermediary layer of electroless nickel between the copper substrate and the solder joint. This nickel layer acts as a diffusion barrier that prevents copper atoms from migrating into the solder and forming brittle inter-metallic compounds, while still allowing the solder to wet the surface effectively. The nickel layer mediates the interaction between copper and solder, eliminating the harmful copper diffusion while maintaining solder joint reliability.
Solution Approach 2:
The patent employs a composite surface finish structure consisting of multiple layers: electroless nickel, electroless palladium, and immersion gold. This composite material system combines the advantages of each layer: nickel provides diffusion barrier properties, palladium offers catalytic activity for electroless plating and good solder wettability, and gold provides corrosion resistance and low contact resistance. The composite structure resolves the contradiction by distributing functions across multiple materials.
2Reliability
If PdAu plating is used, then solder joint reliability is improved, but bath life concerns and maximum current limits are reduced
Solution Approach 1:
The patent replaces the expensive and short-lived PdAu electroplating process with a more economical electroless plating approach. The electroless nickel and palladium layers can be deposited without expensive plating baths that have short lifetimes. This substitution extends the operational duration of the surface finish system while maintaining solder joint reliability, addressing the bath life concern.
Solution Approach 2:
The patent substitutes the electrochemical electroplating process (which requires controlled electrical current and has limited bath life) with an electroless chemical plating process. The electroless plating uses chemical reduction reactions that do not require expensive plating baths with limited lifetimes. This process substitution eliminates the bath life constraint while achieving the same protective and functional properties.
3Manufacturing precision
If additional lithography steps are added to improve surface finish quality, then manufacturing precision is improved, but device complexity and production time increase
Solution Approach 1:
The patent combines the surface finish deposition process with the existing semiconductor manufacturing flow, integrating electroless nickel and palladium plating into the standard fabrication sequence. By merging the surface finish application with the existing manufacturing process rather than adding separate lithography steps, the patent achieves high surface finish quality without increasing device complexity or production time.
Solution Approach 2:
The electroless plating process is self-catalytic and does not require photolithography patterns or masking steps. The chemical reactions occur automatically on exposed copper surfaces, forming uniform nickel and palladium layers without additional lithography equipment or process steps. This self-service characteristic maintains manufacturing precision while avoiding increased device complexity.
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
Enhances solder joint reliability, reduces brittle inter-metallic compound formation, and improves wettability, providing cost-effective and efficient integration of embedded interconnect bridge circuitry dies with improved electrical connections.
Implementation Method 1
forming an electroless nickel layer on the copper pad surface
Implementation Method 2
forming an electroless palladium layer on the nickel layer
Implementation Method 3
forming an immersion gold layer on the palladium layer
Data Source
AI summary
In embodiments herein, a surface finish (SF) is formed on conductive contacts of a package substrate for connection to an embedded interconnect bridge circuitry die. In some embodiments, the SF may be electroless nickel-electroless palladium-immersion gold (ENEPIG). In other embodiments, the SF may be immersion gold-electroless palladium-immersion gold (IGEPIG). In other embodiments, the SF may include a layer of electrolytic palladium-gold on a layer of indium or on a layer of cobalt-iron.