Venkat Kasi1,Amin Zareei1,Sarath Gopalakrishnan1,Rahim Rahimi1
Purdue University1
Venkat Kasi1,Amin Zareei1,Sarath Gopalakrishnan1,Rahim Rahimi1
Purdue University1
Achieving effective and rapid integration of electrical components onto digitally printed conductive traces on flexible substrates, without compromising the electrical and mechanical properties of temperature-sensitive components, has been one of the main challenges in the field of flexible hybrid electronics (FHEs). While convection oven-reflow soldering is the most widely applied method for connecting electrical components onto the traditional rigid printed circuit boards, this high-temperature method is not suitable for flexible substrates and digitally printed components. To address this challenge, we introduced a novel technology, near infrared (NIR) radiation-based technology, as an effective tool for rapid and effective soldering of a lead-free Sn-Bi-Ag solder paste for connecting electrical components onto conductive traces printed on flexible substrates. In this approach, the NIR technology utilizes the highest energy densities to heat certain materials, such as metal particles, via a selective thermal process, while keeping other materials such as polymers at relatively low temperature. Since many polymer substrates including PET have low or negligible absorbance in the near-infrared range, the NIR radiation specifically heats alloy particles in the solder paste and enables them to reach their melting temperature. The conditions such as NIR power and the time of exposure were optimized to obtain improved spreading and adhesion of solder on conductive traces and the substrate. The formation of interfacial region, which represents the degree of soldering process, was investigated using cross-sectional SEM and EDX analysis. As a proof-of-concept, we demonstrated the use of this technology in the fabrication of wearable FHE device that allows the remote assessment of the exudate absorption in wound dressings and indicates the appropriate time for dress change to prevent from any potential infection at the wound site.