What are the Common Circuit Board Materials?

Raw Materials

The substrate most commonly used in printed circuit boards is a glass fiber reinforced (fiberglass) epoxy resin with a copper foil bonded on to one or both sides. PCBs made from paper reinforced phenolic resin with a bonded copper foil are less expensive and are often used in household electrical devices.

The printed circuits are made of copper, which is either plated or etched away on the surface of the substrate to leave the pattern desired. (See "additive" and "subtractive" processes described in step 3 under The Manufacturing Process). The copper circuits are coated with a layer of tin-lead to prevent oxidation. Contact fingers are plated with tin-lead, then nickel, and finally gold for excellent conductivity. Purchased components include resistors, capacitors, transistors, diodes, integrated circuit chips, and others.

Dielectric Materials

A dielectric material is a substance that is a poor conductor of electricity, and used as an insulating layer in the PCB build up. Porcelain, mica, glass, plastics and some metal oxides are good dielectrics. The lower the dielectric loss, (the proportion of energy lost as heat) the more effective the dielectric material. If the voltage across a dielectric material becomes too great -- that is, if the electrostatic field becomes too intense -- the material will suddenly begin to conduct current. This phenomenon is called dielectric breakdown. Rogers 4350 is less likely to demonstrate a dielectric breakdown condition than FR-4.

FR stands for Fire Retardant. FR4 is a glass fiber epoxy laminate. It is the most commonly used PCB material. A 1.60mm FR4 uses 8 layers of (7628) glass fiber material. The red UL/manufacturers logo is in the middle (layer 4). There are two types of logos: red and blue logos. Red is UL94-V0, blue is UL94-HB. If you have a blue logo material, it is either XPC (phenolic) or G10 (glass epoxy); these are older materials. The main usage of G10 nowadays is for thin watch circuit - since it is very punchable. In 1.50/1.60mm FR4 the logo is in the middle layer (layer 4) of the common 8 layer construction. FR stands for Fire Retardant. FR4 is a glass fiber epoxy laminate. It is the most commonly used PCB material. A 1.60mm FR4 uses 8 layers of (7628) glass fiber material. The red UL/manufacturers logo is in the middle (layer 4). There are two types of logos: red and blue logos. Red is UL94-V0, blue is UL94-HB. If you have a blue logo material, it is either XPC (phenolic) or G10 (glass epoxy); these are older materials. The main usage of G10 nowadays is for thin watch circuit - since it is very punchable. In 1.50/1.60mm FR4 the logo is in the middle layer (layer 4) of the common 8 layer construction.

Toxic Materials and Safety Considerations

The solder used to make electrical connections on a PCB contains lead, which is considered a toxic material. The fumes from the solder are considered a health hazard, and the soldering operations must be carried out in a closed environment. The fumes must be given appropriate extraction and cleaning before being discharged to the atmosphere.

Many electronic products containing PCBs are becoming obsolete within 12-18 months. The potential for these obsolete products entering the wastestream and ending up in landfills has many environmentalists concerned. Recycling efforts for electronic products include refurbishing older products and reselling them to customers that don't need, or have access to, newer, state-of-the-art electronics. Other electronics are disassembled and the computer parts are salvaged for resale and reuse in other products.

In many countries in Europe, legislation requires manufacturers to buy back their used products and render them safe for the environment before disposal. For manufacturers of electronics, this means they must remove and reclaim the toxic solder from their PCBs. This is an expensive process and has spurred research into the development of non-toxic means of making electrical connections. One promising approach involves the use of water-soluble, electrically conductive molded plastics to replace the wires and solder.

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