Important PCB Terms for Beginners

For customers, especially those new to the electronics industry, it is imperative to speak the same language as the contract manufacturer. This ensures the possibility to create an accurate representation of design intent without going through painful quoting delays, board redesigns, and redesign efforts. It requires accurate communication from all stakeholders for successful board development. Therefore, Singo recommends customers add PCB design terminology to their basic database. Below is a list of important PCB terms.

Vias help to pass current from one layer to another. For proper board development, the best PCB must be selected through options, as this can affect turnaround time and increase costs in the manufacturing process.

The traces on the PCB are small transmission lines etched from the copper layers by the manufacturer. The signal integrity of a board depends on the parameters of the PCB traces - length, width, impedance, and copper weight. Some applications, such as those with high-speed designs, require coordination between trace design and material selection to ensure optimal signal routing and integrity.

Silkscreen on a circuit board represents an image layer that depicts polarity symbols, component orientation indicators, reference indicators, labels, component packaging, and other identification. Screen printing is an integral step in completing circuit board fabrication. While the absence of this top layer of information does not affect the functionality of the PCB, designers, and manufacturers must include it to eliminate assembly issues and optimize the board manufacturing process.

Signal layers are part of the PCB stack-up. Any layer can be a signal layer as long as it has traces that carry signal currents. Signal planes are distinct from ground or power planes, although they also carry signal currents and are part of the board layers that form the stack up. The signal layer and its surrounding ground or power plane define the trace impedance and contribute to signal integrity.

Proper board operation often depends on efficient signal routing, including the use of ground and power planes. Multilayer boards mostly utilize ground and power planes to improve signal integrity and reduce crosstalk. Designers typically accomplish this with a copper pour that surrounds the entire layer in the form of a ground plane connected to electrical ground or a power plane connected to one of the power lines.

Routing or trace routing is the process of specifying the path that copper traces will take when connecting circuit board elements or components. The netlist created by the designer during schematic capture defines the identity of the traces. By running the process of layout and schematic simulation, you can cross-verify that the traces are successfully routed to the netlist.

Pitch is the length of distance between the centers of adjacent pins or pads of a component. As PCBAs become smaller and denser, so do component packages and their footprints, increasing the space between adjacent pins and component pads, making spacing an important Design Parameter. For components with high pin density, the pitch determines the solder mask process required to avoid assembly problems, including solder bridging.

Accurately created PCB layout patterns are critical during the design phase. This includes the actual footprint or footprint pad layout of each component package in the circuit. This pattern defines where each component goes during assembly and may include polarity markings or reference designators for specific pins.

A PCB fabrication file is a design file that contains all the information, specifications, and images a contract manufacturer needs to fabricate and assemble a circuit board. The most common format is Gerber with multiple files or IPC 2581 which is a CAD file.

The pads on the board define where the pins or leads of the component are located, and the combination of pads forms the footprint of the component. Which package a component will use is an early design decision by the designer, as each package has a number of pads that allow the component to be soldered to the board.

For SMT components, the pads are solid copper shapes on the surface of the board. For through-hole components, the pad has a PTH through-hole that runs through the entire thickness of the board. While most component pads are visible even after assembly, some packages, such as BGAs and CSPs, may hide them beneath their bodies.

Every component on a circuit board has two identifiers or part numbers. One of these is the component number assigned by the manufacturer to its components. The other is a reference identifier, which identifies each component in the board bill of materials and its exact location on the board. While a board may contain multiple components with the same manufacturer's part number, each component will have a unique reference identifier to locate them on the board. 

Manufacturer's part numbers provide traceability as the primary means of ensuring supply chain integrity. Selecting components during the design phase is also essential as the correct selection determines the successful functionality, quality, and reliability of the board.

Design rule checking compares design specifications against a set of guidelines with specific constraints. Standards or DFM parameter ranges can define the basis for these guidelines. Designers must adhere to these constraints, or design rules when creating a PCB layout. These constraints ensure compliance and manufacturability of the PCB assembly.

Cutouts are areas of the board that are removed by design and may include slots. Sometimes these may be required for installation. In some cases, cutouts are part of PCB grounding techniques used to break EMI loop formation. Cutouts can also be milled edges on PCBs, which are sometimes necessary to reduce board thickness. While most circuit boards have a familiar rectangular shape, many applications also use non-standard PCB form factors.

The creepage distance between two entities on a board is the shortest path distance measured along the surface of the board. Design and manufacturing guidelines exist for board assembly and creepage standards for reliable operation.

The gap between two entities on the board is the shortest distance between them. This may include distances in the air, such as gaps across slots. Another example is the distance of components from the edge of the board.

The copper weight of a PCB refers to the amount of copper in the inner or outer layers of the board stacked up. Copper weight is not the total weight of copper on the surface of the layer, but the amount of copper (in ounces) that covers a 1 ft x 1 ft board area. The thickness of copper is directly proportional to its weight.

As more and more applications involve high-speed signal transmission, controlled impedance on circuit board transmission lines is important to maintain signal integrity. By matching material impedance and trace geometry, signal fidelity can be optimized to minimize interference.

The thickness of the board is the total height of the board, not including any components on it. The form factor of electronic circuit boards has been shrinking, primarily to accommodate smaller devices and products. To route more signals, allowing for more functionality and complexity, designers have had to increase the number of layers in a multilayer board stack, thereby increasing the thickness of the board.

A BOM or bill of materials is a list of all the items needed to build a printed circuit board. This list provides information on component part numbers and reference identifiers for all components that will go into the PCBA.

Generally, there are two types of drilled holes that a printed circuit board may have. Holes made during manufacturing can be NPTH, or non-plated through holes, or PTH, or plated through holes. The NPTH type is required for installation. PTH types are vias that are part of the circuit and will carry current. The annular ring is the area of copper around the hole that provides space for solder mask application and proper connection for vias or PTHs.

Before much of the manufacturing process was automated, the industry referred to electronic circuit boards as printed wiring boards. The common name now is printed circuit board or PCB. The term includes both types of circuit boards, those undergoing the manufacturing process and those undergoing assembly. More properly, PCB stands for a circuit board made by a manufacturer without mounted components. The assembled PCB is more of a circuit board, like a computer's motherboard.

A multilayer PCB is a laminated board containing multiple signal layers. Stackup defines the individual layers in the board.

A double-sided PCB is a circuit board with two signal layers. They may have SMC on both sides, THC on one side, SMC on the other, or THC on one side only. The second side is used for enhanced signal routing, with vias for electrical connections from one side of the board to the other.

A single-sided PCB is a circuit board with only one signal layer. Circuitry with copper footprints and pads exists only on the bottom layer of the THC and only on the top layer of the SMC. This is the simplest type of board to manufacture.

These are tiny electronic components available in a variety of packages. The most important aspect of SMCs is that they are completely free of long connecting leads. Instead, they have shooters or end caps that sit on copper pads for soldering. SMCs do not require any mounting holes, which makes them suitable for dense packaging on PCBs. Solder boards with SMC need to go through a reflow oven.

These electronic components are also available in various packages with long connection leads. The THCs require holes to be drilled in the PCB where their leads will go through to be soldered on the bottom. Soldering THC boards require them to be run through a wave soldering machine.

Using common terms benefits both customers and contract manufacturers. It reduces ambiguity, misunderstanding, and confusion, thereby facilitating a smooth manufacturing process. If you still have questions or you are looking for a high-quality PCB manufacturer, welcome to contact us.

Singo is a professional custom PCB board manufacturer. Our company specializes in electronic PCB assembly. Since 2006, mainly engaged in PCB assembly and OEM/ODM electronic manufacturing services. These products include home appliances, digital products, industrial controls and medical equipment. After years of hard work, we have established long-term cooperative relationships with some internationally renowned companies.