Editing Printed circuit board (section)

=== Laminates ===
Laminates are manufactured by curing layers of cloth or paper with [[thermoset]] resin under pressure and heat to form an integral final piece of uniform thickness. They can be up to {{Convert|4|by|8|ft|m}} in width and length.  Varying cloth weaves (threads per inch or cm), cloth thickness, and [[resin]] percentage are used to achieve the desired final thickness and [[dielectric]] characteristics. Available standard laminate thickness are listed in
ANSI/IPC-D-275.<ref>{{cite book |title=IPC-D-275: Design Standard for Rigid Printed Boards and Rigid Printed Board Assemblies |publisher=IPC |date=September 1991 }}</ref>

The cloth or fiber material used, [[resin]] material, and the cloth to resin ratio determine the laminate's type designation (FR-4, [[Composite epoxy material|CEM]]-1, [[G10 (material)|G-10]], etc.) and therefore the characteristics of the laminate produced. Important characteristics are the level to which the laminate is [[fire retardant]], the [[dielectric constant]] (e<sub>r</sub>), the [[dielectric loss|loss tangent]] (tan δ), the [[tensile strength]], the [[shear strength]], the [[glass transition temperature]] (T<sub>g</sub>), and the Z-axis [[coefficient of expansion|expansion coefficient]] (how much the thickness changes with temperature).

There are quite a few different dielectrics that can be chosen to provide different insulating values depending on the requirements of the circuit. Some of these dielectrics are [[polytetrafluoroethylene]] (Teflon), FR-4, FR-1, CEM-1 or CEM-3. Well known pre-preg materials used in the PCB industry are [[FR-2]] (phenolic cotton paper), FR-3 (cotton paper and epoxy), [[FR-4]] (woven glass and epoxy), FR-5 (woven glass and epoxy), FR-6 (matte glass and polyester), [[G10 (material)|G-10]] (woven glass and epoxy), CEM-1 (cotton paper and epoxy), CEM-2 (cotton paper and epoxy), CEM-3 (non-woven glass and epoxy), CEM-4 (woven glass and epoxy), CEM-5 (woven glass and polyester). Thermal expansion is an important consideration especially with [[ball grid array]] (BGA) and naked die technologies, and glass fiber offers the best dimensional stability.

FR-4 is by far the most common material used today. The board stock with unetched copper on it is called "copper-clad laminate".

With decreasing size of board features and increasing frequencies, small non-homogeneities like uneven distribution of fiberglass or other filler, thickness variations, and bubbles in the resin matrix, and the associated local variations in the dielectric constant, are gaining importance.