However, before the copper was bonded to the
printed-circuit board for routing, the copper sheet was pressed
by Carver 2112 laminating press under 6000 lbf/in2 for 15 min
in order to ensure the flatness of the copper. The empirical settings of the prototyping machine for 0.5-mm-thick copper sheet
were the same as that for the core, but the routing depth was
kept at 0.05 mm each time to prevent the mill bit from breaking.
After ten times of routing, the patterned copper winding was
released from the substrate by soaking in the acetone for half an
hour. Fig. 9