Case 2: Heavy copper: Description: 12 layer with inner layer 4oz and outer layer 3oz finish.The dielectric thickness are around 0.1mm(4mil) between each layers, as well as the hole wall thickness required to be 2.4mil. Designs for planar transformers, the upcoming trend in transformers for switch mode power supplies due to the small size and high efficiency(about half the size of wire-wound transformers).The winding based on PCBs give a very high reproducibility with regard to field conditions making switching frequencies up to 1 MHz possible, whereas conventional ferrite wound transformers are limited to 150KHz.