SMD Vs SMT – What is the difference?
With both SMD and SMT growing in popularity, they are often used interchangeably. It is perhaps also because both work hand in hand to offer reliable PCBs. It is, however, important to differentiate between them.
Simply put, SMT refers to Surface Mount Technology, which is an PCB assembly technique that helps arrange components on the circuit board. SMD, on the other hand, refers to Surface Mount Devices. These are components fitted onto the circuit boards. They are designed to be mounted directly on the PCB.
Let us look at both in some more detail:
What is SMT (Surface Mount Technology)?
Surface Mount Technology is a relatively newer way of arranging components on the printed circuit board. Prior to this, components were arranged using through holes where component leads are placed into drilled holes on a bare PCB. Surface Mount Technology, on the other hand, involves soldering the components directly onto the boards. Since there is no need to pass leads through the PCB, the process is far quicker as well as cost-efficient. The big advantage with SMT PCB assembly is that it saves space. What it means is that more components can be housed on a smaller board. In times of miniaturization of devices, its advantage cannot be overstated.
The broad process involved in SMT include:
Printing- This involves applying a coat of solder paste onto the pads of the PCB
Mounting- This refers to placing the surface mount components accurately onto the pads.
Reflow Soldering- This process involves melting the solder paste by passing the board and components through a hot oven.
Testing- The final process involves testing of the boards through processes such as AOI which runs a number of quality checks on the boards such as component alignment and checking for solder bridges.
As is evident from the above processes, SMT is an intricate process that involves applying the right amount of solder paste to mount each component. SMT also lends itself to automation as machines can be programmed to mount components on the PCB in a short time frame. This ensures accuracy while also speeding up the production process and making go-to-market that much quicker.
Some of the other advantages of SMT include:
- Significant savings in weight and real estate.
- Reduced cost of the board as also a reduction in material handling costs.
- Stability and better mechanical performance.
- Components can be placed on both sides of the board and in higher density.
- PCBs created with the surface mount technology process offer higher circuit speed. Also, because SMD components have no leads or have short leads, RF interference is reduced.
- It offers more resistance to vibration and there is less noise.
The drawbacks of SMT however include the fact that it requires a high capital investment that can increase costs, particularly when you are dealing with low volume runs. SMT inspection equipment can also turn out to be very costly. Additionally, SMD components are prone to damage if dropped. Also, the power of such components is generally less.
What is SMD (Surface Mounted Device)?
Surface Mounted Devices are the components fitted onto PCBs. Evolved SMDs use pins that can be soldered directly onto the PCBs as opposed to using leads and wiring them through the circuit board. It enables many more components to be fitted on the board and improving its functionality. With no holes to be drilled, they also make the process quicker and cost-effective.
What is important is to choose the right SMDs and then mount them correctly on the board. SMDs can now be automatically mounted onto the electronic board as opposed to manually soldering them.
Some of the various types of SMD include:
- Chip Resistors
- Network Resistors
- Integrated Circuits
The Overlap between SMD and SMT
The primary difference between the two is that one refers to the mounting process while the other refers to the actual components. However, they are clearly dependent on each other. It is the proper selection and arrangement of SMDs that is the primary process behind SMT. Automated SMT machines can mount several SMDs onto the board in a short period of time. While SMDs determine the capacity of the board, SMT involves the installation of these components on the board.
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