Temperature changes of copper nanoparticle ink during flash light sintering

The copper nanoparticle ink was coated on polyimide substrates using a doctor blade method. The films thus formed were then sintered by flash light irradiation at room temperature under ambient conditions. The flash light energy was varied from 2 J/cm2 to 12 J/cm2. To measure the temperature change, a non-inverting amplifier circuit with an op-amp and a type-K thermocouple was devised. The sheet resistance change was simultaneously monitored using a Wheatstone bridge circuit. An analytical temperature calculation was conducted, considering the heat transfer phenomena during the flash light irradiation. As the results, the temperature of the copper nanoparticle films was reached to (318 °C) in 10 ms at the flash light irradiation energy higher than 12 J/cm2 and they were melted and fully sintered. The analytical solutions of the temperature profile of copper nanoparticles film and polyimide substrate (maximum temperature of copper nanoparticles film and polyimide substrates are 279 °C and 140 °C, respectively) in which the latent heats for phase changes of the copper nanoparticles and the binder (PVP) were concerned, agrees well with the experimentally measured temperature profiles of them (maximum temperature of copper nanoparticles film and polyimide substrates are 318 °C and 135 °C, respectively). The analytical calculation method proposed, could be used to design the flash light sintering variables applicable to various low-temperature flexible substrates.