Minimizing Temperature Gradient in Photonic Sintering for Defect‐Free High‐Conductivity Cu‐Based Printed Patterns by Bidirectional Irradiation

Intense pulsed light (IPL)‐induced photothermal heating is relatively effective at reducing the annealing or sintering time of metal particle‐based conductive patterns in the manufacturing of printed electronics. However, defects such as cavities, delamination, and inhomogeneous shrinkage within the sintered patterns are a well‐known problem in IPL sintering. These defects are considerably influenced by undesired temperature gradients induced inside samples during IPL sintering. To solve this undesired temperature gradient problem, we propose a bidirectional IPL (B‐IPL) sintering approach using front‐ and back‐elliptical reflectors on both sides of the printed pattern. The effects of the B‐IPL energy density and number of shots on the electrical and mechanical properties of the printed patterns were systematically investigated using noncontact spectroscopic temperature sensing techniques with a µs‐timescale infrared temperature sensor system. Cross‐sectional field emission scanning electron microscopy images indicate that B‐IPL sintering significantly enhances the densification level and sintering uniformity of printed patterns compared to conventional IPL. Minimizing temperature gradient in intense pulsed light‐induced photonic sintering is a critical issue for obtaining defect‐free high‐conductivity Cu‐based printed patterns. By employing a bidirectional intense pulsed light sintering using front‐ and back‐elliptical reflectors, temperature gradient is drastically reduced, resulting in fully sintered Cu patterns with high electrical conductivity and mechanical stability.