Duplex Tin Contact Unit for Lead-Free Soldering
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Solution Overview
Problem
Lead-free soldering processes in electronics result in increased thermal loads on contact pins, leading to blistering, dewetting, and whisker formation, which affects solderability and mechanical integrity, and require additional costly galvanizing steps to ensure reliable connections.
Innovation Solution
A contact unit with a duplex tin layer comprising a radially inner matte tin layer and a radially outer bright tin layer, which ensures uniform wetting, mechanical compatibility, and reduces whisker formation, while maintaining mechanical and electrical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If lead-free soldering processes are used, then environmental compliance is improved, but thermal load on contact pins increases causing blisters and dewetting
Solution Approach 1:
The patent applies a composite tin layer structure consisting of multiple layers with different properties: a bright tin outer layer for solderability, a matte tin intermediate layer for stress relief, and a tin-rich core layer. This composite structure allows the contact pin to withstand lead-free soldering temperatures without dewetting or blistering, while maintaining environmental compliance.
Solution Approach 2:
Different layers of the tin coating are given different local qualities: the outer bright tin layer provides good solderability and appearance, the intermediate matte tin layer provides stress relief and prevents dewetting, and the core layer provides structural integrity. Each layer is optimized for its specific function to collectively solve the thermal load problem.
2Productivity
If thermal tearing process is used to produce contact pins, then manufacturing efficiency is improved, but tin layer dewetting occurs at pin tips
Solution Approach 1:
The patent controls the thickness parameters of different tin layers to prevent dewetting during thermal tearing. The intermediate matte tin layer is specifically designed with a thickness of 1-3 μm, which is optimal for preventing dewetting at pin tips during thermal tearing while maintaining manufacturing efficiency.
Solution Approach 2:
The multi-layer tin structure with different mechanical properties allows the contact pin to withstand the thermal stress of the tearing process. The intermediate matte tin layer acts as a buffer zone that prevents the outer bright tin layer from dewetting during thermal tearing, ensuring manufacturing precision while maintaining productivity.
3Reliability
If additional galvanizing step is added, then solderability is improved, but manufacturing effort and costs increase
Solution Approach 1:
The patent applies the tin layer coating to the contact pin before the thermal tearing process, so that the tin layer is already present and properly structured before the pin is separated. This preliminary action eliminates the need for subsequent galvanizing steps, reducing manufacturing complexity while ensuring good solderability.
Solution Approach 2:
The patent combines multiple functions into the initial tin layer coating process: providing solderability, preventing dewetting, and protecting against whisker formation. By merging these functions into a single multi-layer structure applied before thermal tearing, the need for additional galvanizing steps is eliminated, reducing manufacturing effort and costs.
4Ease of operation
If bright tin surface is used, then mechanical compatibility is improved, but blisters form due to outgassing at high temperatures
Solution Approach 1:
The patent applies different local qualities to different layers: the outer bright tin layer provides mechanical compatibility and good appearance, while the intermediate matte tin layer provides stress relief and prevents outgassing. This local differentiation allows the bright tin surface to be used without the harmful effect of blisters.
Solution Approach 2:
The composite tin layer structure with an intermediate matte tin layer between the outer bright tin and the core prevents outgassing from reaching the bright tin surface. The matte tin layer acts as a barrier that stops organic component outgassing, preventing blister formation while allowing the bright tin outer layer to provide mechanical compatibility.
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 duplex tin layer prevents dewetting and whisker formation, ensuring reliable solderability and mechanical compatibility, reducing manufacturing effort and costs, and enhancing the service life of contact units.
Implementation Method 1
the radially inner layer of matt tin ensures uniform wetting of the soldering pin or contact unit even at high soldering temperatures
Implementation Method 2
the duplex layer ensures uniform wetting... prevents dewetting and whisker formation
Implementation Method 3
the contact pins are galvanically provided with a layer of tin. This can be done, for example, in barrel plating, in which a large number of contact pins are introduced into a galvanic bath
Data Source
Figure 1~2
AI summary
The invention relates to a contact unit and particularly a solder pin, and a method for producing a contact unit, comprising a body having a metal core and a tin layer surrounding the metal core. The tin layer is thereby designed as a duplex layer, and comprises a radially inner layer overlay of matte tin and a radially outer layer overlay of glossy tin.