The PWB base material, or laminate, consists of a dielectric material sandwiched by copper foils. Both the copper foil and the dielectric core are manufactured in various sizes. Most PWBs are manufactured on glass woven epoxy-based materials. Other materials are selected for specific electrical, physical, performance or cost characteristics.

Two examples of alternative materials include: high-temperature stable/low-dielectric constant cut to panel size then cleaned mechanically, chemically or by a combination of both. The purpose of this cleaning step, referred to as "pre-clean" is to remove surface contamination, including any anti-tarnish coatings present and to condition the surface copper topography to promote the subsequent adhesion of the photoresist.

Mechanical scrubbing methods include abrasive brush scrubbing and pumice scrubbing. Brush scrubbing removes a thin layer of surface copper, thus ensuring a clean surface, but tends to impart stress to a thin core material by deforming it during the scrub. Brush scrubbing can also produce a surface not compatible with fine-line circuit designs.

Pumice scrubbing imparts less or no stress to the material and produces a favourable surface for photoresist lamination.

Brush scubbing with pumice has been the industry standard for many years. The use of nylon brushes and a suspension of pumice in water results in excellent surface topography. The mechanical action of the brushes tangent to surface has removed a thin uniform layer of oxide and copper. The microscopic action of the pumice particles creates a rough surface of virgin copper. This is ideal for maximum adhesion of all coatings.

Pumice scrubbing can be accompanied by chemical cleaning components e.g. oxalic acid to enhance anti-tarnish removal.

A recent addition to the PWB pumice powder range is 3/OB. This is produced from the same feedstock as 3/ON. A further process of magnetic separation lowers the heavy mineral content and improves purity. It is expected this new grade will gradually replace 3/ON for the majority of surface treatment applications.

A practical example of the financial benefits of pumice brush scrubbing is illustrated in the EnviroSense case study: HML 10061 "Pumice replaces hazardous materials in scouring copper".