Thermoforming Approach for In-Mold LED Arrays Utilizing Screen Printing Process with Silver Paste

Abstract Integrating electronics into three-dimensional devices represents a significant advancement. There are two primary methods for manufacturing 3D electronic products: creating the curved product first and then applying printed electrodes by the non-contact printing method, or printing conductive patterns first on a film, followed by thermoforming. In this study, the latter method was chosen for its ease of manufacturing, cost-effectiveness, scalability, and ability to produce detailed patterns. The previous methods of manufacturing In-mold Electronics (IME) via thermoforming often introduce defects (cracks) that affect circuit conductivity. To fabricate a 3D IME-LED array, screen printing and thermoforming on a Polyethylene Terephthalate Glycol (PETG) substrate was utilized. For the reduction of conduction issues, a silver paste with a polyester resin (thermoplastic) binder was employed. Results demonstrated that the 3D IME circuit demonstrated elongation in length ranging from 5.9 to 6.7% before and after thermoforming, confirming its stretchability. Under optimal temperature of 110 °C and a vacuum level of – 3 psi, resistance decreased by 18%. Additionally, printed lines with a minimal width of 100 μm became conductive following this technique. This was achieved by taking advantage of the paste’s sintering and viscoelastic characteristics during the thermoforming process. This experiment demonstrates a novel approach to integrating electronics into 3D structures, providing valuable insights into the field of IME.