High speed printed circuit boards (PCBs) are disclosed comprising a dielectrics systems with the back-side trenches, prepregs, signal lines and ground-plans, wherein the signal line and ground-plan are located on the dielectrics. Using of the open trenches in the substrate help to reduce the microwave loss and dielectric constant and thus increasing the signal carrying speed of the interconnects. Thus, according to the present invention, it is possible to provide a simple high speed PCB using the conventional material and conventional PCB manufacturing which facilitates the design of circuits with controlled bandwidth based on the trench opening in the dielectrics, and affords excellent reliability. According to this present invention, high speed PCB with the interconnect system contains whole portion or portion of interconnects for high speed chips interconnects and that have have the dielectric system with opened trench or slot to reduce the microwave loss.