How SMT is Assembled on a PCB

SMT is Assembled on a PCB

Until the introduction of surface mount technology (SMT) over 20 years ago, most electronics were assembled through holes drilled into PCBs. SMT allows for components to be placed directly onto the surface of a PCB cutting down manufacturing costs and increasing production rates by automating the process.

When designing a new circuit board it is important to consider how it will be assembled and whether SMT is the best choice for your design. A contractor that specializes in PCB assembly will be able to help you choose the right type of components and advise you on any design changes needed to make your smt pcb board ready. SMT components are usually smaller which may mean that some components must be placed closer together – this can cause problems with signal integrity especially for high-speed devices.

The SMT assembly process starts with the printing of solder paste. A stencil is positioned on the PCB and a tool called a squeegee is used to apply a controlled amount of solder paste to each pad. Solder paste is a putty-like mixture of powdered metal solder and sticky flux. It serves to bond the surface mount pads and clean them of impurities and oxidation.

Once the PCB is fully populated with SMD components it will undergo a heat treatment called reflow. This reflows the solder connections and melts the SMT adhesives ensuring they stick correctly to the PCB. A reflow oven also known as a reflow chamber is required for this step. Automated pick-and-place machines are efficient but have setup and maintenance costs. The complexity of the placement program and the speed of the machine also play a role in the overall cost.

How SMT is Assembled on a PCB

After the PCB is reflow-dried it is passed to an automated optical inspection machine (AOI) where it is tested for quality. This step is crucial to ensuring that the solder joints are of high quality. AOI machines are much faster than humans and are more accurate in their analysis.

If your PCB is a double-sided one it will be passed back to the beginning of the SMT assembly line for component mounting on its other side. Once both sides of the PCB have been completed it will be inspected again for quality by a 3D automated optical inspection machine.

Once all of the steps have been completed the PCBs are then sorted and prepared for shipping. They will be shipped in protective boxes to prevent them from getting damaged during transportation. A label will be printed with the part number and the date of assembly. The reflow soldering process must be tightly controlled to avoid defects. Advanced reflow ovens with precise temperature control are more expensive but necessary for high-reliability applications.

SMT is a great option for electronic manufacturers due to its cost-effectiveness and fast manufacturing. It’s also affordable for consumers who want to purchase a quality product. It is however, important to keep in mind that SMT pcbs are not as durable and rugged as through-hole PCBs as the solder joints don’t offer any protection against mechanical stress. Having said that, if your product is designed with manufacturability in mind using Better DFM tools you can avoid most problems caused by this method of assembly.

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