The next layer is thin copper foil, which is laminated onto the plate by heating and adhesive. On the common double-sided PCB, heavy copper is applied to both sides of the substrate. In lower cost electronics, only copper may be on one side of the PCB. When we refer to double-sided or 2-Ply plates, we mean the number of heavy copper layers in a thousand layers (2). It can be as low as 1 layer, up to 16 layers or more.
The thickness of copper can vary and is specified in weight, in ounces per square foot. Most PCBs have an ounce of copper per square foot, but some PCBs that handle very high power may use 2 or 3 ounces of copper. An ounce per ounce can be converted to a copper thickness of about 35 microns or 1.4 inches.
What is a PCB?
Printed circuit board is the most commonly used name, but it can also be called “printed circuit board” or “printed circuit card”. Before the advent of PCB, the circuit was built through the arduous point-to-point wiring process. When the wire insulation begins to age and break, this will lead to frequent faults and short circuits at the wire connections.
The development of winding is an important progress. In this case, a small wire is actually wound around the column at each connection point, thus forming a highly durable and easily replaceable air tight connection.
As electronics move from vacuum tubes and relays to silicon and integrated circuits, the size and cost of electronic components begin to decline. Electronic products are becoming more and more common in consumer goods. The pressure to reduce the size and manufacturing cost of electronic products has prompted manufacturers to seek better solutions. So PCB was born.
PCB is a bit like a layer cake or lasagna – there are alternate layers of different materials that are laminated together by heating and adhesive, so the result is a single object.
The top layer of heavy copper foil is called solder mask. This layer makes the PCB green (or red in sparkfun). It covers the copper layer to insulate the copper wire from other metal, solder or conductive drill bit in accidental contact. This layer helps the user weld the solder in the correct position and prevents solder jumpers.
In the following example, the green solder mask is applied to most PCBs, covering small traces, but the silver ring and SMD pad are exposed, so they can be soldered to them. The solder mask is usually green, but can be almost any color. Red is used for almost all sparkfun boards, white for ioio boards, and purple for lilypad boards.