What Material is a Printed Circuit Board (pcb) Made Of?
A printed circuit board (PCB) is typically a flat laminate composite made from a non-conductive substrate material with copper circuit layers buried on the inner or outer surface.
They can be as simple as one or two layers of copper, or they can have fifty layers or more in high-density applications. Flat composite surfaces are ideal for supporting components that are soldered and attached to the PCB, while copper conductors electronically connect components to each other.
The five basic components of a standard printed circuit board are:
Prepreg
Laminate
Copper foil
Solder mask
Nomenclature
Prepreg is a thin glass fabric that is coated with resin and dried in a special machine called a prepreg processor. Glass is the mechanical substrate that holds the resin in place. Resins--usually FR4 epoxy, polyimide, Teflon, and other resins--start to coat the fabric in liquid form. As the prepreg passes through the processor, it enters the oven section and begins to dry. Once it leaves the processor, it is dry to the touch.
When the prepreg is exposed to higher temperatures, typically above 300 degrees Fahrenheit, the resin begins to soften and melt. Once the resin in the prepreg melts, it hits a point (called thermoset) and then re-hardens, hard again, very, very strong. Despite this strength, prepregs and laminates tend to be light. Prepreg or fiberglass is used to make many things-from boats to golf clubs, airplanes, and wind turbine blades. But it is also critical in PCB manufacturing. Prepregs are the material we use to bond PCBs together, and they are also the material used to build the second component of the PCB, the laminate.
Laminates, sometimes called copper-clad laminates, consist of sheets of prepreg laminated together by heat and pressure, with copper foil on each side. Once the resin hardens, the PCB laminate is like a plastic composite with copper foil on both sides.
We image and etch copper foil to create circuits on the laminate surface. These copper circuits will become conductors or wires on the inner and outer layers of the board. When the laminate layers are imaged and etched with the circuit, they are then laminated together using the prepreg discussed earlier.
Soldermask is the green epoxy coating that covers the outer circuitry of the board. The internal circuitry is buried in the prepreg layer, so no protection is required. However, if left unprotected, the outer layer will oxidize and corrode over time. A solder mask provides protection for conductors on the outside of the PCB.
The nomenclature, or silkscreen as it is sometimes called, is the white letters you see on top of the solder mask on the PCB. The nomenclature is a letter that shows each component's position on the board, and sometimes component orientation.
Soldermask and nomenclature are available in other colors besides green and white, but these are the most popular.
The solder mask protects all circuits on the outer layers of the PCB on which we are not going to connect components. But we also need to protect the exposed copper vias and pads where we plan to solder and mount components. To protect these areas and provide a good solderable surface, we typically use metallic coatings such as nickel, gold, tin/lead solder, silver, and other final surfaces designed for PCB manufacturers.
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