copper to act as a ground plane for shielding and imprimate fabricare circuite power return. For microwave printed circuits, transmission lines can be laid out in a planar form, such as stripline or microstrip, with dimensions carefully controlled to ensure consistent impedance. In RF and fast switching circuits,
to prevent solder shorts, the coating is called circuite imprimate fabricare a solder mask. Soldermask is generally green in color but can have different colors: green, red, blue, white, black. Only the outer layers need to be covered with solder mask, the inner copper layers are protected by the adjacent substrate
layers). Among the multi-layer imprimate circuite fabricare PCBs, the most common are the four-layer ones. The four-layer board has many more routing options in the internal layers compared to the two-layer board, and often part of the internal layers are used as a ground plane or power plane, to achieve better