There are usually contrasting materials that make up printed circuit boards. One is designed to be extremely conductive, while the other is designed to be completely non-conductive. But before discussing the materials, it is important to know the context of using these materials. Knowing the structure of a printed circuit board will make it easier to understand the use of these materials.
Printed Circuit Boards’ Basic Structure
The single-sided board represents the most basic structure of a printed circuit board. This type of board has a single substrate with two different sides. One side of the board houses the electronic components. The other side of the board is where the electric tracks are laid out. The boards substrate should be made of non-conductive material. The substrate is usually rigid and rectangular, although non-conventional designs exist today as well as flexible and semi-rigid boards. The tracks on one side of the board are usually made of super-conductive materials. The tracks are mounted, laminated, or etched to the board. They are responsible for electrical connections, like miniaturized wiring.
Conductive Materials for the Circuit
A typical printed circuit board uses copper foil for its electrical tracks. Copper is relatively inexpensive compared to other metals and is highly conductive, too. This is the reason why copper is commonly used in making electrical wiring for appliances. Not to mention that it is extremely malleable so it can be contorted to fit even the most complex of printed circuit board designs. The use of copper reduces manufacturing costs and allows a steady flow of electricity throughout the circuit.
Non-Conductive Materials for the Substrate
On the other hand, the boards substrate is usually made from FR-4 Epoxy. FR-4 Epoxy is the industry standard material made out of glass epoxy reinforced by plastic. Woven fiberglass cloth is melded with an epoxy resin binder. This makes the FR-4 Epoxy not only non-conductive but also extremely flame resistant. This is important because there are a lot of electrical components today that heat up pretty quickly, like the core processing units of modern computers. It is also important for the substrate material to have a high melting point. Should the quality be substandard, there is a high risk for the boards components to short circuit or worse, explode.
Another material that can be used to make the circuit boards substrate is FR-2 Paper or Phenolic. FR-2 Phenolic is a kind of synthetic resin bonded paper. Wood fiber is reinforced with phenolic polymers like plasticized phenol formaldehyde resin. This gives it a brownish look and it is commonly used for the printed circuit boards of basic consumer electronics. This material has can withstand up to 105 degrees Celsius which is more than enough for basic use.
What is “FR”?
The FR is the grade designation of the materials used. FR is the short term for flame retardant and is a rating of the flammability of the particular material in use. Most of todays computers and appliances have complicated circuitry and printed circuit board designs. That is why the FR-4 is the industry standard because of its high flame resistance. Circuit boards that use FR-4 are usually brominated. This is because bromine has high flame resistance properties.
The transition of electronics to smaller and smaller form factors has led manufacturers to come up with unconventional designs. To fit printed circuit boards in non-traditional casings or at least provide electrical connections that cannot otherwise be done on traditional board designs, flexible and semi-rigid board have been made. The material for these boards wildly vary as this piece of technology is still in its infantile stages (although it is now widely used for consumer electronics). A common material used for these types of boards is flexible conductor layers printed on dielectric film.