Submillimeter-thick loop heat pipes fabricated using two-layer copper sheets for cooling electronic applications

•A novel submillimeter-thick loop heat pipe using two copper sheets was developed.•A grooved structure was formed in the thin copper sheet to generate capillary force.•A nonwoven fabric consisting of copper fibers was used to maintain the liquid phase.•A thin loop heat pipe of 0.4 mm thickness achieved a thermal resistance of 0.21 K/W.•An ultrathin loop heat pipe with a thickness of 0.4 mm achieved a thermal resistance of 0.21 K/W at 7.5 W. A new submillimeter-thick loop heat pipe (LHP) fabricated using two copper sheets is proposed as a cooling solution for thermal management of electronics. The experimental investigation was conducted by measuring the temperature of each part of the surface of the thin LHPs for its heat input, to evaluate the heat transport characteristics of the LHPs discussed in this paper. Submillimeter LHPs with thicknesses of 0.6 and 0.4 mm were fabricated using chemical etching and diffusion bonding processes on two thin copper sheets. A design is exhibited that achieves efficient heat transfer under a variety of operating orientations with a thin LHP, by using a half-etching process on a thin copper sheet to form a grooved structure that generates capillary force. A thermal resistance of 0.09 K/W between the evaporator and the condenser is achieved at 5 W in the top heat orientation, using a nonwoven fabric consisting of copper fibers located inside the flow path of one of the copper sheets. Moreover, it is demonstrated that heat transport can be achieved up to a heat input amount of 7.5 W without orientation dependence for an ultrathin LHP of 0.4 mm thickness.