Steps in the Surface Mount PCB Process

The surface mount pcb process enables the attachment of component leads to the flat surfaces on a printed circuit board instead of through holes. It can be done automatically with machines for high volume production and provides a more compact, flexible and cheaper board. This technology allows smaller components to be used as well as increased circuit density compared to through hole mounting. It also increases the level of functionality that can be achieved in a circuit board.

The first step in the surface mount pcb process is the application of solder paste to the pads on the board. This is done using a stencil to ensure that the solder paste is only applied to the pads on the board where it is required. The solder paste is made up of a carrier, flux, and solder balls (often called spheres). Eutectic solder paste is the most commonly used.

Once the solder paste has been applied, the components are placed onto the PCB. This can be done manually for low-volume or prototype work, or automatically with a pick and place machine. The PCB is then passed through a reflow oven that heats the solder to a temperature at which it melts, forming a solid and mechanically reliable connection between the component and the pads on the PCB.

What Are the 3 Steps in the Surface Mount PCB Process?

In the case of double-sided boards, both sides of the board are passed through reflow soldering cycles. The final step in the surface mount pcb assembly process is the inspection of the completed board by an automated machine, known as an AOI (Automated Optical Inspection) machine. This is done to check that the solder joints have not failed and that all the components are in the correct position. AOI machines are now available that use 3D imaging to make this more reliable than the older 2D versions which tended to produce false positives.

One advantage of the surface mount pcb assembly process over traditional leaded electronic components is that the lead sizes can be reduced, making the circuit board smaller and lighter. However, this is offset by the need to have additional circuitry to deal with the increased power requirements of SMD components. The lower power ratings are also a disadvantage in some applications, for example, a surface mount resistor can dissipate far less energy than a standard leaded resistor of the same value.

A further benefit of the surface mount pcb process is that it can be used on both sides of the circuit board, enabling components to be mounted closer together. This helps to reduce interference coupling between tracks on the circuit board and is particularly useful when the circuit requires a large number of input/output signals. This increase in connectivity enables the development engineer to achieve more functionality in a small volume of integrated circuits. This in turn enables more advanced devices to be manufactured at a lower cost than would be possible with traditional through-hole techniques.