PCB Assembly Layer Technical Terms
Besides knowing how PCB is layered, you should know technical terms accompanies the use of PCBs:
• Annular ring. The copper ring that surrounds the holes on a PCB.
• DRC. An acronym for design rule check. Essentially, DRC is a practice whereby the design of a PCB is checked for its functionality. Details that are checked include the width of the traces and drill holes.
• Drill hit. Used to describe all holes on a PCB, whether correct or misplaced. In some cases, a hole might be slightly incorrect due to dull drilling equipment used during the production.
• Finger. Metal exposed along the board edge that serves as connecting points between two PCBs. Fingers are most often found on old video games and memory cards.
• Mouse bits. A PCB section overly drilled to the point where it threatens the board's structural integrity.
• Pad. An area of exposed metal on a PCB, onto which a soldered piece is generally applied.
• Panel. A large circuit board consisting of smaller boards, which are eventually separated for individual use.
• Paste stencil. A metal stencil on a board, onto which paste is placed for soldering.
• Plane. A larger section of exposed copper on a PCB, which is marked by borders but lacks a path.
• Plated through hole. A hole that goes straight through a PCB, usually for the purpose of connecting another component. The hole is plated and usually features an annular ring.
• Slot. Any hole that isn't circular. PCBs with slots are often high priced due to the production costs of creating odd-shaped holes on a circuit board. Slots are typically not plated.
• Surface mount. A method whereby external parts are mounted directly to PCB without through holes.
• Trace. An ongoing line of copper across a PCB.
• V-score. A place where the board has been partially cut. This can render a PCB vulnerable to snapping.
• Via. A hole through which signals travel between layers. Tented versions are covered with protective soldermask, while the untented vias are used for connector attachments.
The number that precedes a PCB assembly layer refers to the exact number of conducting layers, be it a routing or plane layer - the two layer types. Layers tend to have the number 1, or any of the next four even numbers: 2, 4, 6, 8. Layer boards sometimes have odd numbers, but these are rare and would make hardly any difference. For example, the PCB material in a 5 layer or 6 layer board would be virtually identical.
The two layer types have different functions. Routing layers feature tracks. Plane layers serve as power connectors and feature copper planes. Plane layers also feature islands that determine the signaling purpose of a board, be it 3.3 V or 5 V.
FR4 is code name for glass-reinforced epoxy laminated sheets. Due to its strength, as well as its ability to withstand moisture and fire, FR4 is one of the most popular PCB materials.