Printed Circuit Substrate Materials (PCB/PWB)
Printed circuit materials have copper-clad surfaces for the fabrication of electronic and electrical circuitry on printed circuit boards (PCBs), printed wiring boards (PWB) and flexible circuits. They include materials for flexible film circuit and membrane switches, as well as rigid laminates for circuit boards. Specifications for printed circuit materials include dimensions such as width, length and thickness; thermal properties; physical and mechanical properties; and electrical parameters.
Selecting Printed Circuit Materials
When selecting printed circuit materials, temperature resistance, thermal conductivity, and coefficient of thermal expansion (CTE) are most important thermal properties to consider. Peel strength or adhesion, flexural strength, tensile strength, and elongation are basic physical and mechanical properties. Electrical parameters for printed circuit materials include electrical resistivity, dielectric strength, dielectric constant or relative permittivity, and dissipation factor. Some products are tested according to published standards or test methods developed or adopted by the Institute of Printed Circuits (IPC), an organization that was formerly known as the Institute of Interconnecting and Packaging Electronic Circuits.
Laminates and laminated printed circuit materials are used to produce rigid boards. Laminate types include multilayer, prepreg, cored, hollow core, and specialty products. Multilayer laminates consist of multiple plys of glass, wood, metal, plastic, fabric, or foam. Prepreg materials are made of woven cloth or nonwoven materials that are saturated with uncured or partially cured B-stage resin. The prepreg is supplied to the fabricator and molded into a shape such as an antenna substrate, radome or enclosure. Core materials consists of solid wood or wood-product core (OSB, particle board), honeycomb, foam, corrugated sheet, internal trusses, or lattice block structures. Lattice or trusses can be formed by bonding and expanding wire screen or perforated metal sheet. Hollow-core printed circuit materials have a hollow pocket with minimal webbing between the skins or faces.
Printed circuit for flexible circuits (flex circuits) and membrane switches include a variety of tapes and films. Typically, adhesive tapes and films consist of a backing coated with one or two layers of pressure sensitive adhesive (PSA). Transfer tapes or film adhesives do not have a backing, and consist of an adhesive film packaged on liners. Printed circuit materials for flexible circuits also incorporate special various. For example, some products provide electrostatic discharge (ESD) control, chemical resistance, or shielding against electromagnetic interference (EMI) or radio frequency interference (RFI). PCBs and materials that are die-cut or include embedded passives are also available. Metallized products have a metallized layer, metallic appearance or thin-film coating. Printed circuit materials with a moisture or vapor barriers may be suitable for some demanding applications.