A Printed Circuit Board Assembly (PCBA) is composed of a wide variety of components, each playing a distinct role in enabling the functionality of the overall electronic system.

　　Integrated circuits (ICs) are among the most prominent components on a PCBA. Microcontrollers are a type of IC that acts as the "brains" of many electronic devices. They are programmed to perform specific tasks, such as controlling the operation of a home appliance, processing data from sensors in an industrial control system, or managing the functions of a mobile device. Application - specific integrated circuits (ASICs) are designed for a particular application, like the dedicated graphics processing ASICs in gaming consoles that are optimized for high - speed, high - resolution graphics rendering.

　　Passive components are also abundant on a PCBA. Resistors are used to control the flow of electric current. They come in different resistance values and are crucial for tasks such as voltage division and current limiting. Capacitors store electrical energy and are used for filtering out noise in power supplies, coupling signals between different parts of a circuit, and in timing circuits. Inductors, on the other hand, store energy in a magnetic field and are often used in power converters, where they help in converting one voltage level to another.

　　Semiconductor components like diodes are present. Diodes allow current to flow in only one direction and are used in rectifier circuits to convert alternating current (AC) to direct current (DC). Light - emitting diodes (LEDs) are a special type of diode that emit light when current passes through them. They are used for indication purposes, such as power - on indicators in electronic devices, and in lighting applications.

　　Transistors are another important category of components. They can be used as amplifiers to increase the strength of an electrical signal or as switches to control the flow of current in a circuit. Field - effect transistors (FETs) are commonly used in modern electronic circuits due to their high input impedance and low power consumption.

　　Connectors are essential for making electrical connections between different parts of a PCBA or between the PCBA and external devices. They come in various forms, such as pin - headers for connecting daughter - boards, USB connectors for external device connectivity, and power connectors for supplying electrical power to the PCBA.

　　In addition, there are sensors on some PCBA. Temperature sensors, for example, are used to measure the temperature of the device or the environment. They are common in devices like laptops to prevent overheating by controlling the cooling system. Proximity sensors can detect the presence or absence of nearby objects and are used in applications such as automatic door openers and mobile device proximity - based features.