Printed Circuit Board Components Identification — Rush PCB

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Rush PCB makes several types of printed circuit boards, along with PCB assemblies. For our customers it is necessary they can identify common circuit board components. This identification may be necessary even for assemblers, testers, and those involved with troubleshooting printed circuit boards in the field.

Aluminum PCBs

Circuit Board Component Identification—Broad Classification

Primarily, there are two types of components on any printed circuit board assembly:

  • Mechanical Components
  • Electrical Components

Mechanical Components

The major mechanical component is the printed circuit board itself. It provides mechanical support to all the components. Mechanical components are mainly for providing secondary support to the printed circuit board assembly, and are not involved in any electrical function. They can be fasteners, stiffeners, heat sinks, mounting hardware, and so on.

Mechanical components are easy to identify, as they do not have any electrical connections attached to them. They may be made of different metals depending on their functionality—for instance, heat sinks are usually made of aluminum, fasteners and stiffeners may be made of steel, mounting hardware may be copper, bronze, or steel, and so on.

Mounting hardware may be steel screws or bolts, but some of them may also be made of engineering grade plastic. They may connect with single components on the board, or may form isolated arrangements.

Electrical Components

Electrical components will usually connect to the printed circuit board either through wires or direct soldering. Broadly speaking, a printed circuit board assembly can have two types of electrical components:

  • Through-Hole Components
  • Surface Mount Components

Through-Hole Components

Through-hole components are usually large sized and with long leads that require a hole in the printed circuit board to mount. The leads of through-hole components travel through the hole to the other side of the board, where they attach to pads with solder.

Surface Mount Components

These are small components, typically mounted on the top side of the printed circuit board. They do not need holes for mounting, as their leads are very short. Solder binds surface mount components to copper pads on the top side of the board.

Whether they are through-hole or surface mount, it is possible to subdivide all electrical components into:

  • Passive Electrical Components
  • Active Electrical Components

Passive Electrical Components

Passive electrical components do not have any additional means to control the flow of electricity through them. It is easy to identify most of them, as they have two leads. There are various types of passive electrical components like resistors, capacitors, inductors, batteries, fuses, and transducers. The silk screen printing on the printed board can help in their identification.

Identifying Resistors

It is possible to identify through-hole resistors by the color code printed on them. They have a longish body, usually blue or green with bands of different colors signifying their value, tolerance, etc. Resistors of higher wattage, above 1 W may have a brown color, with their value printed on them. Resistors of still higher wattage, above 5 W, may be white, made of rectangular ceramic material, and have their values printed on them.

Resistors of surface mount type may be more difficult to distinguish from capacitors, especially if they are very small. Looking like a grain of sand, these 0201 size surface mount components do not have enough body space to carry any markings on them. Bigger surface mount resistors may have their value printed on them.

Hint: The silk screen printing on the board next to a resistance will usually begin with an R.

Identifying Capacitors

There are various types of through-hole capacitors. The easiest to identify is the electrolytic capacitors, which look like small vertically standing cylinders. Their value, voltage rating, and temperature ratings are printed on their body. One of the terminals may be marked, as electrolytic capacitors are polarized.

Small value ceramic through-hole capacitors look like a small flat disc with two terminals. Their value and voltage rating is printed on the body of the disc.

Other types of through-hole Mylar and Polyester capacitors may look like a small rectangular objects with two leads. Their body is large enough for printing their value and voltage rating.

Electrolytic surface mount capacitors look very much like their through-hole counterparts, with the leads missing. Most other surface mount capacitors look similar, with a rectangular body. Depending on the value and voltage rating, these surface mount capacitors may be very tiny or somewhat bigger.

Hint: The silk screen printing on the board next to a capacitor will usually begin with a C.

Identifying Inductors

Identifying through-hole inductors from through-hole resistors is very difficult, as both look very similar in physical construction. However, the value printed on the body can identify them—marking on resistors will be in Ω, kΩ, or MΩ, whereas those on inductors will be in µH, mH, or H.

Identifying surface mount inductors may be easier, provided one can see the ferrite former and the wire winding on it. Hermetically sealed inductors may look very much like surface mount capacitors.

Hint: The silk screen printing on the board next to an inductor will usually begin with an L.

Identifying Batteries

Batteries on a printed circuit board usually have a holder and therefore, are easier to identify. They may be cylindrical or coin-shaped. Modern Lithium-ion batteries are usually rectangular, and may have a green or blue shrink-wrapping. Their voltage and ampere-hour rating is usually printed on their body.

Hint: The silk screen printing on the board next to a battery will usually begin with an B.

Identifying Fuses

It is easy to identify a glass cartridge fuse as these have a glass body through which the fuse wire is visible and end caps that fix to clips soldered in the board.

However, other types of fuses may also be present that look like a through-hole resistor. Surface mount fuses also look very much like resistors.

Hint: The silk screen printing on the board next to a fuse will usually begin with an F.

Identifying Connectors

Connectors connect wires or flat cables to the printed circuit board. They will have multiple pins either through-hole type or surface mount type. They can be large for other connectors to plug into them or slim type to allow flat flex cables to connect to them.

Hint: The silk screen printing on the board next to a connector will usually begin with a K.

Active Electrical Components

Active components can usually control the electrical signal passing through various means. A huge variety of active electrical components are available, in both through-hole and surface mount variety. Most common among them are:

  • Diodes
  • Transistors
  • Integrated Circuits


These are simple two-terminal active components. Most through-hole diodes are small cylindrical shapes with leads protruding from them. One end has a marking to denote the cathode. Some diodes may have black opaque bodies, but some may look like transparent glass cylinders.

Surface mount diodes may be more difficult to identify from surface mount resistors, but the diode will have a polarity marking that is not present on the resistor.

Hint: The silk screen printing on the board next to a diode will usually begin with a D.


These are usually three-terminal active components, but some may also have four terminals. The through-hole transistor is easier to identify, as they have a plastic or metal body with the leads protruding from one side.

The surface mount transistor is also easy to identify, as the body will have three or four terminals.

Hint: The silk screen printing on the board next to a transistor will usually begin with a Q.

Integrated Circuits

These are the easiest to identify on a printed circuit board assembly. The through-hole versions are usually in-line packages with a long body and a number of leads on one or both the long sides. Two types of through-hole integrated circuits are more common:

  • Single-in-line package — one line of leads
  • Dual-in-line package — two lines of leads

Surface mount integrated circuits have more variety. Apart from the dual-in-line package, they can have a quad packaging, or a ball grid packaging, where the pins are below the integrated circuit.

Hint: The silk screen printing on the board next to an integrated circuit will usually begin with a U.


Printed circuit board component identification may be easier if there is a silk screen printing on the board. Circuit board assemblies from Rush PCB usually have schematics and a bill of materials, where the designer denotes each component beginning with an alphabet followed by a serial number.