Embedded Die Surface Finish Using CoFe-Pd-Au for Solder 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 for conductive contacts in integrated circuit packages face issues such as solder joint reliability (SJR) concerns, copper diffusion, and formation of brittle inter-metallic compounds (IMCs) when nickel is omitted.
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 SJR concerns and reduce IMC formation, while also allowing for cost-effective and faster process implementation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If nickel is omitted from the surface finish to reduce IMC formation, then copper diffusion is reduced, but solder joint reliability deteriorates
Solution Approach 1:
The patent introduces an electroless nickel layer as an intermediary between the copper pad and the solder joint. This nickel layer acts as a mediator that prevents direct copper-solder interaction (reducing harmful copper diffusion and IMC formation) while still providing reliable solder attachment. The nickel layer is deposited electrolessly to ensure uniform coverage without requiring additional copper, thus resolving the contradiction between reducing copper diffusion and maintaining solder joint reliability.
2Reliability
If a multi-layer surface finish is implemented to improve solder joint reliability, then copper diffusion is reduced, but manufacturing complexity increases
Solution Approach 1:
The patent extracts and eliminates the immersion gold layer from the traditional ENEPIG process, implementing only electroless nickel followed by electroless palladium. This simplification maintains the core benefits of copper diffusion prevention and solder joint reliability while reducing manufacturing complexity by removing one deposition step and eliminating the need for gold materials.
3Manufacturing precision
If electroless plating is used to deposit surface finish layers, then manufacturing precision is improved, but production time increases
Solution Approach 1:
The patent employs electroless plating processes for both nickel and palladium deposition, which are self-catalytic and continuous processes. The autocatalytic nature of electroless plating allows uniform metal deposition across complex geometries without interruption, maintaining high manufacturing precision while achieving continuous production flow that maximizes deposition efficiency.
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 proposed surface finishes enhance solder joint reliability, improve wettability, and reduce the formation of brittle IMCs, providing better current carrying capacity and uniform tin wicking, thus ensuring stable connections and reducing fabrication costs.
Implementation Method 1
forming an electroless nickel layer on the copper pad
Implementation Method 2
electrolytic cobalt-iron-palladium-gold as a surface finish
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.