Selective Tin Coating Reflow for Connector Whisker Control
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Solution Overview
Problem
In strip electroplating, existing methods struggle to selectively melt partial areas of tin-plated coatings while preserving the galvanic crystallization structure in other areas, leading to issues like whisker formation and mechanical stress in connectors.
Innovation Solution
A method involving a locally and temporally selective reflow process using a pulsed infrared laser to apply heat only to specific small areas of the coating, allowing for structural transformation without affecting the rest of the coating, utilizing a deflection scanner for precise heat application and maintaining the coating's integrity in press-fit zones.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the entire coating surface is heated to melt the coating, then the coating achieves low internal stress and accelerated intermetallic phase growth, but the galvanic crystallization structure is destroyed in areas where it should be preserved
Solution Approach 1:
The heating process is segmented into multiple independently controllable heating zones along the coating strip. Each zone can be heated separately to achieve selective structural transformation in specific areas while preserving the galvanic structure in other areas, resolving the contradiction between achieving low stress/accelerated phase growth and preserving galvanic crystallization structure.
Solution Approach 2:
Different regions of the coating are subjected to different thermal treatments: some areas undergo heating above the melting point to achieve low internal stress and accelerated intermetallic phase growth, while other areas are heated below the melting point to preserve the galvanic crystallization structure. This local differentiation of thermal quality resolves the contradiction between achieving desired coating properties and preserving original structure.
2Force
If the coating is heated above the melting point for structural transformation, then low insertion and removal forces are achieved, but thermal conduction to the base material causes the entire coating to melt
Solution Approach 1:
The heating system is divided into multiple independently controllable heating zones with individual temperature control. This allows specific zones to be heated above the melting point to achieve low insertion and removal forces through structural transformation, while other zones are maintained below the melting point to prevent unwanted melting, overcoming the limitation of thermal conduction in highly conductive base materials.
Solution Approach 2:
The heating zones are dynamically controlled with independent temperature regulation, allowing the system to adaptively heat different areas to different temperatures based on the desired structural transformation. This dynamic control enables precise temperature distribution management despite the high thermal conductivity of the base material.
3Manufacturing precision
If two separate operations are used to treat different coating areas differently, then selective structural transformation is achieved, but production time and process complexity increase
Solution Approach 1:
Multiple heating zones with different temperature profiles are merged into a single continuous processing line. This allows selective structural transformation in different coating areas to be achieved in one continuous operation rather than requiring separate processing steps, thereby maintaining manufacturing precision while significantly improving productivity by eliminating the need for repositioning and second operations.
4Productivity
If pure tin coating is used for environmental reasons, then lead-free connectors are produced, but whisker formation occurs causing short circuits
Solution Approach 1:
The thermal parameters are changed by heating the pure tin coating to above its melting point in specific zones, inducing structural transformation that eliminates the conditions favorable for whisker formation. This parameter change (temperature-induced structural transformation) maintains environmental compliance by using pure tin while eliminating the harmful whisker formation through controlled heating and structural modification.
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
This approach enables precise structural transformation in press-fit zones, reducing whisker formation and mechanical stress, while maintaining the coating's quality and preventing dewetting of edges, resulting in improved mechanical properties and performance in connectors.
Implementation Method 1
a pulsed infrared laser is used as the heat source
Implementation Method 2
A laser arrangement is used as the heat source. In particular, the laser arrangement has a pulsed infrared laser
Implementation Method 3
the melting temperature of the coating is exceeded, so that a structural transformation takes place in the small area
Implementation Method 4
In this way, a structural transformation or reflow in the indium coating is achieved
Data Source
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AI summary
In a method for coating a component (2), a coating (4) comprising a first material structure (M1) is applied on the component (2) and subsequently, in a transformation region (6a), a structure transformation is carried out to form a coating (4) of a second material structure (M2), the transformation region (6a) is divided into small regions (8a-h) and the respective structure transformation only takes place in one of the small regions (8a-h) within a respective short time span (Ta-h), wherein no structure transformation takes place outside of the respective small region (8a-h) within the short time span (Ta-h). The procedure is used for a component (2) of a connecting device in press-fit technology.