Aruna Kumarasiri
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Strengthening Electrical Standards in Load Cell Design

Aruna Kumarasiri > Completed > Strengthening Electrical Standards in Load Cell Design

Collaborators

University of Moratuwa
Public University in Sri Lanka
Flintec Inc.
Global Load Cell Manufacturing Company (Branch: Koggala, Sri Lanka)
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A Typical load cell design

Outcomes
Lead Free Solder Compatibility Improvement on Nichrome Alloy Through Contact Angle Modification
Scientific article, IEEE
(Winner, Best Paper Award)
Surface Wettability Analysis of Nichrome Alloy Based on the Measurements of Sessile Droplet Contact Angles
Scientific article, IEEE
A Novel Technique to Measure Contact Angles of Sessile Droplets
Software and Instrument

My Contribution

I carried out this research while working as a Research and Development Engineer at Flintec Inc., Sri Lanka—a global leader in load cell manufacturing. This project allowed me to make a direct contribution to the global market while strengthening my skills in teamwork, communication, and conflict resolution.

Research

Concept development

Technical design

Testing and Validation

Collaboration and Communication

Case Summary

This project focused on improving the solderability and mechanical reliability of Evanohm® R alloy tabs used in precision resistors. The original tabs had issues with poor solder wetting and delamination, which affected product performance. A new surface treatment and plating process was developed, using a nickel coating. The updated process significantly improved adhesion, passed multiple reflow cycles, and showed strong results in peel tests. 

Background

  • Evanohm® R, a nickel-chromium-based alloy, is commonly used in precision resistor manufacturing due to its stable resistance properties and excellent high-temperature performance. As part of the resistor's internal structure, the tabs made from Evanohm® R serve as crucial points for electrical contact and thermal dissipation. However, in practical applications, the team encountered persistent issues related to poor solderability and delamination. These defects not only increased rework and inspection time during assembly but also raised concerns about the long-term reliability of the solder joints.
  • The primary objective of this project was to engineer a plating process that could enhance solderability and mechanical adhesion of the tabs to SAC305 solder preforms. By improving the quality and consistency of the plated tabs, the team aimed to bolster production efficiency and ensure that the final resistor assemblies met stringent reliability requirements.

Case Information

  • Duration

    January 2020 - July 2021

  • Category

    Research & Development

  • Role

    R&D Engineer

  • Context

    Novel technique to improve the solderability of Ni20Cr alloy

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Problem Statement

  • Upon initial examination, multiple batches of Evanohm® R tabs displayed weak solder wetting behavior during reflow soldering. In several cases, solder preforms failed to form a complete bond with the tab, leading to partial adhesion, cold joints, or visible delamination. Post-reflow mechanical peel tests often revealed poor joint strength, which could compromise mechanical and electrical performance under thermal or vibrational stress. These failures were traced back to inconsistencies in the surface condition of the incoming tab material, particularly the presence of native oxides and surface contamination, which interfered with both plating adhesion and solder wetting.
  • The nature of Evanohm® R alloy itself—being highly oxidation-prone—further complicated the challenge. Traditional cleaning methods did not consistently remove oxide layers effectively, especially on aged or improperly handled stock. These insights underscored the need for a carefully designed surface treatment and plating process tailored to the unique chemistry of the Evanohm® R alloy.

Project Approach

  • The project team initiated a comprehensive review of surface treatment and plating methods suitable for Evanohm® R. Initial trials focused on surface activation strategies, ranging from light mechanical abrasion to acid-based etching.
  • It became evident that mechanical polishing alone was insufficient, as oxide layers quickly re-formed unless chemical passivation was controlled. The team then developed a multi-step pre-treatment protocol involving degreasing, acid etching, and multiple deionized (DI) water rinses to ensure consistent oxide removal and a receptive surface for plating.
  • Electroplating trials centered on the use of a nickel barrier layer followed by a gold finish (Ni/Au). Nickel was chosen for its role as a diffusion barrier and structural anchor, while gold served as the solderable outer layer due to its inertness and excellent wetting characteristics. Plating thicknesses were optimized to ensure durability without introducing unnecessary material costs.

Key Findings

  • One of the clearest conclusions from the experimental data was that surface condition prior to plating played a critical role in solder joint quality. Tabs that bypassed the pre-cleaning and oxide-removal process showed unreliable solder wetting, often failing to meet minimum peel strength requirements. Conversely, tabs that underwent the complete pre-treatment and plating procedure consistently exhibited strong, cohesive solder joints.
  • The Ni/Au plating combination emerged as the most robust solution. Gold provided excellent solderability even after multiple thermal cycles, while the underlying nickel layer ensured strong adhesion to the base metal. This stack significantly reduced occurrences of peeling or cold joints during reflow.

Outcomes

  • By implementing the revised plating process, the team achieved a significant reduction in solder joint failures. The process proved effective across varying batches of tab material, demonstrating tolerance to minor variations in incoming stock conditions. This improvement translated into reduced rework, higher throughput in assembly lines, and stronger product reliability in the field.
  • Beyond addressing the immediate technical issue, the new plating protocol has laid the groundwork for a more standardized tab preparation process. Its modular steps make it easily adaptable for other product lines or similar alloy systems.
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Contact angle measurement instrument

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Adhesion testing machine

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Nickel plated strain gauges

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Current efficiency vs plating time

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EDX test on plated tabs

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Scanning electron microscope (SEM) images of nickel coatings deposited on Ni20Cr at different current densities

Lessons Learned

  • A major takeaway from this project was the importance of tightly controlled surface preparation, especially when working with oxide-prone alloys. Even seemingly minor inconsistencies—such as slight delays between cleaning and plating—could lead to substantial differences in adhesion quality. This underscored the need for standardized dwell times, chemical concentrations, and rinse procedures throughout the pre-treatment stage.
  • Another valuable insight was the benefit of combining empirical testing with process optimization. While plating recipes can often be selected based on standard practices, tailoring the process to the specific material and application proved essential for achieving consistent, reliable results.

Future Directions

  • Looking ahead, the team has identified several opportunities to further refine the process. One avenue includes evaluating alternative plating stacks—such as palladium-nickel or silver-based finishes—for applications requiring different thermal or mechanical performance thresholds. 
  • Environmental considerations are also being explored, particularly in regard to the gold plating bath. Investigations into lower-waste or cyanide-free gold plating alternatives may help reduce the environmental footprint of the process without compromising performance.
  • Finally, the integration of inline surface condition monitoring prior to plating could offer early-stage quality assurance, ensuring that only suitably prepared tabs proceed to the plating step. This would further improve process control and reduce material waste.

Images courtesy: macrovector & fatmawatilauda

Explore Other Projects

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Solderability Enhancements on Nichrome Alloy

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Strengthening Electrical Standards in Load Cell Design

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