Terminal Finish Sealing Plating Breaks to Prevent Corrosion
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Solution Overview
Problem
The reliability of semiconductor device leads is compromised due to corrosion and metal migration caused by reactive species in harsh environments, particularly when tin and nickel-palladium-gold stacks are used, as they can form dendrites and expose underlying copper surfaces during mechanical processing.
Innovation Solution
A conductive terminal finish featuring a nickel-palladium-gold plating stack with breaks is applied, which is then coated with a solder finish to protect the underlying base material from corrosion, using processes like plating, dipping, or vapor-deposition with corrosion-resistant solder alloys like tin and eutectic combinations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a plating stack (nickel-palladium-gold) is applied to protect the base material, then corrosion resistance is improved, but breaks in the plating stack expose the underlying copper surface to reactive species
Solution Approach 1:
The solder finish is selectively applied only at the locations where breaks in the plating stack are present, rather than coating the entire terminal surface. This localized application seals the exposed copper areas while preserving the protective plating stack in intact regions, thereby addressing corrosion resistance locally where needed without compromising the overall protective structure.
Solution Approach 2:
A solder finish acts as an intermediary material between the exposed copper base material and the reactive species in the environment. This intermediate layer prevents direct contact between the reactive species and the copper surface, thereby eliminating the harmful chemical reactions that would otherwise occur at the break sites in the plating stack.
2Ease of manufacture
If tin and nickel-palladium-gold plating is used to protect leads, then solderability is improved, but dendrite formation and metal migration occur in harsh environments
Solution Approach 1:
The harmful tin material that forms dendrites is selectively removed from areas where it causes problems (at the breaks in the plating stack), while the protective plating stack structure is preserved. The solder finish is applied only where needed to seal breaks, rather than applying a continuous tin layer that would be prone to dendrite formation across the entire terminal surface.
Solution Approach 2:
The terminal structure employs a composite material system consisting of multiple layers: the base copper material, the multi-layer plating stack (nickel-palladium-gold), and the solder finish applied at break locations. This composite structure combines the advantages of each material while mitigating their individual disadvantages, particularly preventing dendrite formation by avoiding continuous tin coverage while maintaining solderability at critical locations.
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 solder finish effectively seals breaks in the plating stack, reducing corrosion and metal migration, thereby enhancing the reliability and longevity of semiconductor device leads in harsh industrial environments.
Implementation Method 1
using processes like plating, dipping, or vapor-deposition with corrosion-resistant solder alloys
Data Source
AI summary
In described examples, a terminal (e.g., a conductive terminal) includes a base material, a plating stack and a solder finish. The base material can be a metal, such as copper. The plating stack is arranged on a surface of the base material, and includes breaks in the plating stack. The breaks in the plating stack extend from a first surface of the plating stack to a second surface of the plating stack adjacent to the surface of the base material. The solder finish is coated over the breaks in the plating stack.