A basic PCB starts with a copper-clad fiberglass material or thin copper sheets adhered to either side of the board.
With a multilayer board (a board with more than two copper layers), a piece of Pre-Preg may be placed between these cores to create one solid board with several copper layers. Pre-Preg is made of material similar to the core with additional adhesive that will adhere it to the layer above and below.

Printed Circuit Board made of

Core material is a rigid sheet of fiberglass resin material that has two sheets of copper adhered to either side. Some material may have a copper sheet on only one side. The copper is measured in ounces (oz). PCB manufacturers will refer to the copper thickness in ounces, but during board lay-up, or when the materials are stacked together, the inch/mm thickness is used.

Pre-Preg material is made of similar material as the core material but is in a soft, pliable form and comes in standard-sized thin sheets.

Copper foil is a thin sheet of copper that is placed on or between Pre-Preg materials and bonds to the Pre-Preg with the adhesive that is part of the Pre-Preg.

Copper plating is primarily used only on the finished board, on the external layers, and provides an additional thickness of copper to the board while plating the wall of the holes drilled in the board. Usually the external plating is added after the board is drilled and the external copper on the board is etched, leaving a thicker trace.

Solder flow is a process in which solder is applied to the external surfaces of the board on exposed copper areas. This helps prepare the board for soldering and protect the copper from oxidation. The copper areas on the entire board may be solder flowed, or a process called SMOBC (Solder Mask Over Bare Copper) will be used. SMOBC process is when the board is “masked” and only the exposed area (usually pads or areas that are to be soldered) will be coated with solder flow.

Solder mask is a material that is used to coat the board to:

  • Protect from surrounding environment.
  • Insulate the board electrically.
  • Protect against solder bridges.
  • Protect components mounted to the board.
  • Protect the board from heat generated from components mounted to the board.

The Trace – a trace on/in a PCB is relative to a wire. It provides the same function of transferring electricity from one point to another while the strength of the PCB provides a rigid material to place components on. The copper layers, as explained later, will each go through an etch process that removes unneeded portions of the copper, leaving only those traces and pads required.

The Pad - a pad may consist of several different shapes and styles. Normally two types of pads are used, commonly referred to as a soldered surface-mount pad or a soldered thru-hole pad. A surface mount pad is nothing more than a square or rectangular copper area that is used for mounting surface-mount components. The size and shape depend on the component that is mounted/soldered to the pad. Most component manufacturers have recommended pad sizes for their components.
A soldered pad may consist of a plated thru-hole pad (PLTH) or a nonplated thru-hole pad (NPTH). Both are nothing more than a round, square, or oblong pad with a hole through the pad. This allows a leaded component to be mounted to the board by placing the lead through the hole and the lead soldered to the pad area.

The plated hole, consists of a pad in almost any shape with a hole through the pad. The walls of the hole are surfaced or plated with copper and, in some cases, solder or some other protective plating. The plating in the hole extends from the external area and flows into the hole, “plating” the hole wall.

Slots and Cutouts are similar to plated/non-plated thru-holes but are defined separately because of their shapes and characteristics. PLTH/NPTH are usually round holes but not always round pads, but the hole is drilled. A slot or cutout is cut into the board by a router bit and is an oval, oblong, or a rounded square shape. The “corner” of a slot or cutout is not square unless a special corner punch is used. Slots and cutouts are cut with a round bit; therefore the corner must be the radius of the bit, or larger. The router bit size depends on board thickness and manufacturer’s capabilities. A small bit may be used on a thick board but must cut slowly to prevent breakage, increasing time and cost.

The board edge deserves its own definition and attributes, due to the values that define the board edge. The board edge is any part of the board that exposes the cross section of the board, including slots, cutouts, and the outer edge of the board.


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