Fig. 1. Shape and size of experimental copper foil and liquid crystal polymer (LCP)

Fig. 2. Laser flattening of copper foil. (a) Pulsed laser system; (b) schematic of laser flattening; (c) laser spot moving path in laser flattening process

Fig. 3. Laser imprinting of copper foil. (a) Schematic of laser imprinting; (b) nano-structure of silicon mold surface

Fig. 4. Laser welding of copper foil and LCP. (a) Continuous laser system; (b) schematic of laser welding; (c) schematic of welding sample size

Fig. 5. Surface images of flattened copper foil taken by atomic force microscope

Fig. 6. Surface roughness of copper foil. (a) Surface roughness of copper foil flattened under different pulsed energies and 50% overlap ratio; (b) surface roughness of original copper foil; (c) surface roughness of copper foil flattened under different overlap ratios and pulsed energy of 0.35 J

Fig. 7. Surface images of copper foil taken by scanning electron microscope. (a) Original copper foil; (b) transition area；(c) flattened copper foil

Fig. 8. Cross-section morphology of flattened copper foil

Fig. 9. Optical surface morphologies of samples. (a) Optical morphology of ultra clear glass surface; (b) schematic of flattening; (c) optical morphology of flattened copper foil surface

Fig. 10. Surface roughness comparison of copper foil before and after annealing. (a) Comparison of surface roughness of flattened copper foil before and after annealing; (b) comparison of surface roughness of original copper foil before　and after annealing

Fig. 11. SEM surface morphologies of copper foil before and after annealing. (a) (b) Flattened copper foil；(c) (d) original copper foil

Fig. 12. Surface morphologies of nanomold under different magnifications

Fig. 13. Surface morphologies of imprinted copper foil under different magnifications

Fig. 14. Bonding strength between copper foil and LCP under different treatment conditions. (a) Tensile test bench system; (b) bonding strength between copper foil and LCP; (c) tensile curve of original annealed copper foil welded with LCP; (d) tensile curve of flattened annealed copper foil welded with LCP; (e) tensile curve of flattened annealed imprinted copper foil welded with LCP

Fig. 15. Variations of copper foil surface roughness under different treatment conditions. (a) Surface roughness values of different copper foils; (b) AFM surface images of different copper foils