IC Socket Contact Pin Plating for Sn Diffusion Control
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Solution Overview
Problem
Conventional contact pins in IC sockets experience a rapid increase in electrical resistance due to alloy formation at high test temperatures, leading to premature exposure of underlying layers and reduced service life during burn-in tests.
Innovation Solution
A socket with a laminated electrical connector structure, featuring a first layer of Pd-Ni or Pd-Co alloy with a lower Sn diffusion speed and a second layer of silver or silver alloy, which slows down Sn diffusion, thereby reducing alloy formation and extending the number of tests before electrical resistance rises abruptly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a gold plating layer is used on contact pins, then good initial electrical contact is achieved, but Sn diffusion occurs at high temperatures causing alloy formation and increased electrical resistance
Solution Approach 1:
The plating layer is segmented into multiple functional layers: a diffusion barrier layer (Pd, Pt, or Rh) that prevents Sn diffusion, and a surface layer (Au, Ag, or Ru) that ensures good electrical contact. This segmentation resolves the contradiction by assigning different functions to different layers, preventing alloy formation while maintaining contact reliability.
Solution Approach 2:
The diffusion barrier layer acts as an intermediary between the Sn-containing connection terminals and the contact pin material. It mediates the interaction by blocking Sn diffusion while allowing the surface layer to maintain electrical contact, thus preventing harmful alloy formation without compromising contact quality.
2Reliability
If the burn-in test temperature is increased to 150°C or higher, then better reliability testing is achieved, but the diffusion speed of Sn increases causing faster exposure of underlying layers
Solution Approach 1:
The diffusion barrier layer serves as a thermal and diffusion intermediary that remains stable at high temperatures. It blocks Sn diffusion even when the test temperature is increased to 150°C or higher, allowing reliable testing without accelerating harmful alloy formation.
Solution Approach 2:
The invention changes the material parameters of the plating layer by selecting elements (Pd, Pt, Rh) with high thermal stability and low Sn solubility. This parameter change enables the plating layer to resist Sn diffusion at elevated temperatures while maintaining its protective function.
3Stability of the object's composition
If a Pd plating layer is used to prevent Sn diffusion, then alloy formation is reduced, but the diffusion barrier effectiveness decreases at high temperatures
Solution Approach 1:
The plating layer is constructed as a composite structure combining a diffusion barrier layer (Pd, Pt, or Rh) with a surface layer (Au, Ag, or Ru). This composite material approach leverages the high thermal stability and low Sn solubility of the barrier layer while adding the excellent electrical contact properties of the surface layer, achieving both composition stability and barrier reliability at high temperatures.
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 solution effectively delays the exposure of underlying layers and maintains electrical contact integrity, extending the service life of the IC socket by reducing the frequency of abrupt electrical resistance increases during high-temperature burn-in tests.
Implementation Method 1
a first layer made of a material in which a diffusion speed of tin is lower than that of palladium... and a second layer made... of a material in which the diffusion speed of tin is lower than that in the first layer
Data Source
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AI summary
Contact pins are provided in a socket main body into which an IC package is accommodated and brought into electrical contact with connection terminals of the accommodated IC package. Each contact pin is formed of a plurality of layers obtained by laminating an underlying layer containing Ni and a surface layer successively on a conductive base material. Furthermore, the surface layer includes a first layer on an underlying layer side, and a second layer in contact with the connection terminals of the IC package. The first layer is formed of a plating layer of which a principal ingredient is a Pd-Ni alloy which is a material lower in diffusion speed of Sn than that of Pd, among materials into which Sn dissolves and diffuses by applying heat. The second layer is formed of a plating layer of which a principal ingredient is Ag which is a material lower in diffusion speed of Sn than that of the first layer.