PCB Components and Assembly

1/27/2019 | 5 min read

Printed circuit boards (PCBs), essential electronic building blocks, are found in almost all modern electronic equipment including computers, mobile phones, and home appliances such as washing machines and dryers.

PCBs are made from glass-reinforced plastic boards. Cut into these boards are interconnected lines and pads known as traces, through which electrical current flows, powering the different circuit board components and routing electrical inputs and outputs to these components. Power and signals are conducted through the copper traces to reach their intended connections on the board, similar to the way in which copper wire connects other electrical components.

The Basic PCB Layers and Components

Two types of PCBs are single-sided and double-sided. As their names would suggest, single-sided PCBs only have one copper layer going through one side while the other side is reserved for the components.

Double-sided PCBs, on the other hand, have two or more layers installed on their sides, each with their own copper traces. As the complexity of circuit designs increases, multilayer boards become essential because of the need to route the copper traces without compromising the circuit integrity or introducing conditions such as crosstalk.

Despite their numerical layer differences, both PCB types have a solder mask and silkscreen sitting on top of the copper layer. The solder mask insulates the copper from contact with any metal parts and accounts for the green color typically seen in PCBs. Sitting on top of the solder mask is the silkscreen, on which letters and numbers can be seen as a guide when assembling the PCBs. Even with the solder mask, some metal parts remain exposed, allowing other components to be soldered onto them.

Discrete PCB components include resistors, LEDs, transistors, capacitors, inductors, diodes, switches, and a battery, which each perform a specific function. The color-coded resistors, for example, control the magnitude of electric current by altering the electrical resistance of the circuit path. LEDs indicate the presence of a current flow, transistors amplify current, and capacitors store electrical charge. Switches are used to pass or block current, and batteries provide a DC voltage for the circuit. The electrical design dictates which of these devices are utilized and where they are mounted in the final PCB application.

PCB Assembly

There are two methods to attach components to a PCB: through surface-mount technology (SMT) or the through-hole method. The use of SMT involves mounting and soldering components on the PCB surface, while the through-hole method mounts components through leads inserted into holes in the PCB. Regardless of the method used, assembly of the PCB must follow the pattern available on the silkscreen to solder and attach the different components to the board. Extra care must be taken to ensure that metal components do not touch each other, as this can cause a short-circuit on the board. Once all components have been mounted, the PCB is ready for inspection and test prior to its installation into a device.

Due to their sensitive nature, PCBs must be carefully protected when in use. Sealant potting and encapsulants, for example, can help to protect the PCBs once they have been assembled to ensure they can withstand the environmental conditions anticipated by their end application.

Conclusion

Playing a critical role in a broad range of products, PCBs represent the key building blocks of electronics devices that serve today's market. With the ability to customize design options to match the complexity of the circuit, PCBs offer a proven, repeatable technology to achieve cost savings and provide reliable performance for almost any industry requirement.

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