Patent ID: 8458894

Claim:
A method for making a positive temperature coefficient device, comprising: (a) first forming a crosslinkable preform of a positive temperature coefficient polymer composition containing a polymer system and a conductive filler; (b) then attaching a pair of electrodes to the crosslinkable preform; (c) next soldering and hot pressing a pair of conductive leads to the electrodes using a lead-free solder paste having a melting point greater than 210° C. in a hot pressing machine; (d) next crosslinking the crosslinkable preform after step (c); and then (e) thermally treating the crosslinked preform after step (d) by iteratively repeating the process of heating the crosslinked preform to the first working temperature and then cooling the crosslinked preform to the second working temperature for a plurality of times, wherein soldering and hot pressing the conductive leads to the electrodes is conducted by applying a pressure to the conductive leads that ranges from 10 psi to 50 psi.