Development of Thin-Film-Based Sensors for Smart Weldability Estimation of Industrial Solder Tips

In this work, we describe the design, simulations, fabrication, and characterization of a sensor aimed at weldability estimation of industrial solder tips employed in robotic solder stations. The proposed solution is based on a matrix of thin-film resistive sensors that are individually tested for the assessment of a solder tip weldability and are fabricated on a silicon wafer using planar process techniques and redistribution layers (RDLs). Taking advantage of standard microfabrication techniques, a 200-mm silicon wafer can accommodate thousands of temperature sensors, whose electrical resistance can be monitored during periodic weldability tests of the tip under evaluation. During each weldability test, the solder tip contact causes a localized temperature increase that causes a measurable increase in the electrical resistance of the thin-film resistive sensor being thermally actuated. Prototype wafers were fabricated and tested in laboratory with actual solder tips, and the results show that important parameters, such as a time-constant and the temperature increase measured in each test can be employed to estimate the weldability condition of a solder tip, allowing for the implementation of smart predictive maintenance and optimized replacement routines with no need to halt the production line. The high density of weldability sensors that can be microfabricated on the wafer allows the manufacture of low-cost sensors and results in a compact, adaptable, high-volume fabrication solution that supports sustainable practices in the scope of Industry 4.0.