**Takashi Nakamura 1,\* ID , Hea Jeong Cheong 2,†, Masahiko Takamura <sup>3</sup> ID , Manabu Yoshida <sup>2</sup> ID and Sei Uemura <sup>2</sup>**


Received: 24 July 2018; Accepted: 13 August 2018; Published: 14 August 2018

**Abstract:** Copper nitride particles have a low decomposition temperature, they absorb light, and are oxidation-resistant, making them potentially useful for the development of novel wiring inks for printing circuit boards by means of intense pulsed light (IPL) sintering at low-energy. Here, we compared the thermal decomposition and light absorption of copper materials, including copper nitride (Cu3N), copper(I) oxide (Cu2O), or copper(II) oxide (CuO). Among the copper compounds examined, copper nitride had the second highest light absorbency and lowest decomposition temperature; therefore, we concluded that copper nitride was the most suitable material for producing a wiring ink that is sintered by means of IPL irradiation. Wiring inks containing copper nitride were compared with those of wiring inks containing copper nitride, copper(I) oxide, or copper(II) oxide, and copper conversion rate and sheet resistance were also determined. Under low-energy irradiation (8.3 J cm<sup>−</sup>2), copper nitride was converted to copper at the highest rate among the copper materials, and provided a sheet resistance of 0.506 Ω sq<sup>−</sup>1, indicating that copper nitride is indeed a candidate material for development as a wiring ink for low-energy intense pulsed light sintering-based printed circuit board production processes.

**Keywords:** copper; copper nitride; photo sintering; ink; paste; printed electronics; post-processing
