Carbon-based composite conductive ink (3CI) has some challenges to its properties. Here, combined with the application of 3CI on silicon keypads, a series of studies on the electrical, mechanical and thermal performance of 3CI has been conducted by adding specific concentrations of silver powder, silica powder and SiO2@Ag core-shell particles. The properties of the modified 3CI were characterized by using the four-point probe tester, scanning electron microscope, Rockwell hardness tester, cross-cut tester and laser thermal conductivity analyzer. The experimental results revealed that by adding silver powder with a particle size of 20 microns equivalent to 12% by weight of the 3CI, ink resistance decreased by 76%, from 8.44 kΩ/□ to 2.03 kΩ/□. Meanwhile, adding silica can increase the ink’s tensile strength and thermal diffusivity while improving the adhesion of the 3CI on the silicone rubber. It was worth noting that when the particle size of the SiO2@Ag core-shell particle was smaller than that of the added silver powder, the resistance of the 3CI was further reduced. Finally, a modified 3CI with the adhesion of 4B, a conductivity of about1 kΩ/□, a hardness of 232 HV0.5, and a thermal diffusivity of 0.217 cm2s−1 was achieved experimentally, which provided an experimental basis for the modified 3CI suitable for silicone keypads.