I conducted this research as an undergraduate researcher at the University of Moratuwa, Sri Lanka, in collaboration with Flintec Inc., a global leader in load cell manufacturing. In addition to generating valuable insights for both the materials science field and industry applications, this project helped me strengthen my skills in instrumentation, data analysis, and scientific communication.
In collaboration with an industry partner, this project explored how to improve the solderability of nichrome (Ni/Cr) alloys. Using a combination of experimental testing and image processing techniques, we evaluated how surface treatments like ZnCl₂/HCl pre-treatment and nickel electroplating affect solder drop behavior. The results showed that removing the passive oxide layer on nichrome surfaces significantly improves wettability, making solder joints more reliable.
Nichrome (Ni/Cr) alloys are commonly used in various industries because of their excellent electrical properties and availability. However, a thin layer of chromium oxide on these alloys can make soldering difficult. This case study explores two methods to improve soldering by enhancing wettability, making it easier for solder to adhere to the nichrome surface.
Keywords: Nichrome, Wettability, Contact Angle, Solderability, Electroplating
Nichrome alloys are essential in technologies like heating elements and sensors. They have desirable properties, such as a low temperature coefficient of resistance and high resistivity, making them suitable for applications like strain gauges. However, soldering nichrome thin films is more challenging compared to other materials like constantan and nickel. This study investigates ways to improve solderability and addresses the issues caused by the chromium oxide layer.
January, 2018 -
January, 2020
Research
Undergraduate Research Assistant
Novel technique to assess and improve solderability on Nicrome alloy
Enhancing the wettability and solderability of nichrome alloys is crucial for various industries, particularly in electronics. In consumer electronics, reliable solder joints are essential for maintaining electrical connections in devices like smartphones and laptops, leading to increased customer satisfaction through fewer failures and longer lifespans. In the automotive industry, improved solderability ensures robust connections in complex electronic systems, preventing malfunctions that could jeopardize safety. Similarly, in aerospace applications, solder joints must withstand extreme temperatures, making enhanced solderability vital for safety and reliability. Moreover, improving solderability can lead to significant cost savings by reducing defective products and material waste in manufacturing processes. As electronics become smaller and more advanced, enhanced solderability allows for better compatibility with emerging technologies and sustainable materials, aligning with industry efforts to transition to lead-free solder alloys.
(a) Solder Dots Observation by Using A Microscope (b) Captured Image of a Solder Dot by Microscope
We treated nichrome thin films with a solution of ZnCl₂ and HCl to eliminate the chromium oxide passivation layer. Solder droplets were formed at high temperatures (325-350°C) and then analyzed to measure how well they adhered to the surface.
We created a special device that uses a digital microscope to capture images of solder droplets. These images were then processed with software we developed to measure the contact angles, helping us assess how well the solder spreads on the surface.
To measure how strong the solder joints were, we used a tensile testing machine to pull on the solder dots. This helped us understand how well the solder adhered to the nichrome film.
We applied a nickel electroplating process to the nichrome thin films, using a three-step method that included cleaning and preparing the surface. We adjusted factors like current density and plating time to optimize the quality of the nickel coating.
Contact Angle Calculation Processed By (a) Polynomial Fitting Method (b) Ellipse Fitting Method
Graphical user interface of the developed software for the contact angle measurements
Contact angle measurement device and software setup
A CAD design of the adhesion testing machine
Our results showed that treating the nichrome films with the ZnCl₂/HCl solution significantly reduced the contact angles of the solder droplets, improving wettability. The average contact angle decreased from 118.7° to 47.8°, indicating much better adhesion. The adhesion strength of the solder joints was also strong, ranging from 40 to 45 Newtons.
Further experiments with nickel electroplating confirmed that this method also enhanced wettability. As we increased the current density during plating, we observed a consistent decrease in contact angles, leading to better solderability.
The contact angle measurement software we developed proved to be highly accurate, with a low mean absolute error (MAE) of ±1°. Our experiments confirmed that we could enhance the wettability of nichrome alloys by removing the passivation layer and applying a nickel coating. This improvement can lead to more reliable solder joints in various applications.
The techniques developed in this study have practical implications for industries that rely on reliable soldering in electronic devices. By using the methods outlined, companies can:
Working with Flintec, we demonstrated how these improvements could be applied in real-world settings, showcasing their effectiveness in a production environment. This case study serves as a valuable resource for future research and industry applications in enhancing solderability.
Images courtesy: macrovector & fatmawatilauda
