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What Is Surface Mount Technology

pcbonline PCBONLINE Team Thur, May 21, 2020

Printed Circuit Boards, or PCBs, are one of the more important technologies that have emerged in the 20th century.

Their use has, all the more accelerated, as the world becomes increasingly advanced in terms of science and technology, with its use being felt in every aspect of our lives.

There is much that can be said about the design of the PCBs, and everything else that goes into it.

One of the many principles used in the manufacture of PCBs is that of what is called ‘Surface Mount Technology’.

It is one of the key aspects of the modern PCB industry, and it is found almost everywhere, from the simplest circuits to the more complex and highly integrated ones.

There is much that can be said about ‘Surface Mount Technology’, from their basic designs to their more advanced aspects.

Some of the key details of the same are explained in the points below.

1.) The Term & Basic Introduction

The concept of "Surface Mount Technology", or SMT, is a core principle that goes into the design of PCBs, due to the nature of the way the chips are made.

In the design, the chip’s many components, ranging from ICs to resistors and other complex assemblies, are essentially mounted on the surface of the board, from which the principle gets its name.

The way that the manufacturing process works, goes along the lines of a standard board being prepared as per industry standards, after which the desired components are ‘placed’ on the board in predesignated points, after which they are bonded, usually through soldering or other means.  

2.) Purpose of Surface Mount Technology

For a very long time, the PCB industry has used the ‘through-hole’ construction principles, where the components are bonded to the board, by placing their leads or other parts through a drilled hole in the board.

This, however, has proven to be a rather cumbersome and lengthy process, which is why it has increasingly made it necessary for other techniques, one of which is surface-mount technology.

The surface-mount technology has proven itself to be especially useful, in the context of automation, where the process allows for large-scale production of PCBs, in comparison to the system which made use of ‘through-hole’ construction designs.  

3.) General Understanding of the Principle

While much can be said about the way the principles work, it can be understood as an alternative to the use of wires.

Rather than having the components use wires or lead to carry signals or electricity, they are simply ‘placed’ on the surface, through the use of solder or other such materials.

What Is Surface Mount Technology

4.) History of Surface Mount Technology

The use of Surface Mount Technology is nothing new, although its increased application is a rather recent trend. The early designs of the technology were by the company IBM, with the technology itself being referred to as ‘Planar Mount’ rather than ‘Surface Mount’.

It traces its origins back to the 1960s, the same time when other developments in the world of technology were also taking place. At the same time, however, the technology was largely ‘shelved’, in favor of through-hole principles.

It began to make a resurgence in the 1980s, and took off about a decade ago, with the large-scale adoption of technology in every aspect of our lives. It should be noted here that in addition to its widespread adoption in recent times, it has evolved considerably with the passage of time as well.

5.) Advantages of Surface Mount Technology

Several advantages exist when it comes to the use of Surface Mount Technology in the design of PCBs.

Some of the key advantages are listed out in the points below:

1. The process is generally faster in comparison to the use of through-hole design principles, meaning that the production is generally faster. This adds up to both times as well as cost savings for the manufacturer and the client. In turn, the same is passed on to the customer, who can benefit from cheaper products.

2. Although the principle is called ‘Surface Mount Technology’ and is touted as an alternative to drilling holes in the board, it is not always the case that no holes are drilled, although it is often the case. In many cases, fewer holes are drilled than what would otherwise have been the case.

3. When it comes to the components used for the same, they tend to be cheaper for those which use Surface Mount Technology, when compared to that of through-hole ones.

4. Another important advantage of Surface Mount Technology is that it allows for the placement of components on both sides of the circuit board, as opposed to just one. This, in turn, allows for the manufacture of more highly integrated chips, which are faster and more powerful, but at the same time use an equivalent or lesser amount of space than before.

5. The size of the Surface Mount Technology components is generally smaller, which allows for a higher density of the components on the board.

6. The technology allows for higher structural integrity, especially in harsh conditions such as that of shake and vibration-related environmental stresses.

6.) Disadvantages of Surface Mount Technology

As much as Surface Mount Technology has its advantages, there are a few drawbacks that need to be taken into account as well.

Some of the key drawbacks of the technology include, among others, the following:

1. The technology is not suitable for all components. On the contrary, there are certain components, such as those that are large or require a large amount of power, which require a through-hole construction to work properly in the PCB.

2. The low size of many components used in Surface Mount Technology can make repairing the PCBs very difficult.

3. Components that require frequent connections and disconnections are unsuitable for using Surface Mount Technologies.

To sum up, there is much more than what is mentioned about, which can be said about the use of Surface Mount Technology.

The above is but a general introduction and understanding of the same and nothing more, about this new fabrication principle that is steadily being adopted across the PCB industry. 

How well do you know PCB SMT Assembly Technology?

Assembly Technology

Surface mount technology has stabilized and matured the manufacturing process.

It consists of several main steps and sub-steps which may be different from purpose to equipment.

One step is to attach components to the substrate.

It consists of several main steps and sub-steps which may be different from purpose to equipment.

Surface mount adhesives are used to hold components in place before wave or reflow soldering.

The adhesives provide other functions such as thermal conductivity, chemical inertness, and dielectric properties.

These adhesives are classified by the grade of cure like heat only, UV, and ambient cure. These adhesives can be either thermoplastic or thermosetting.

Adhesives are applied in three methods: printing, pin transfer, or dispensing.

The location and pattern of the adhesives are very important to prevent components from falling during soldering.

Over-application of adhesive can lead to solder joints.

Another main step is the application of soldering fluxes.

These help to remove surface contaminants and oxidation from soldering surfaces. (leads, pads, and hols)

Some of the soldering flux types require cleaning after the Soldering process.

Flux is cleaned either from solvent-based or aqueous-based solutions.

General steps of surfacing mounting:

  • Apply Solder Paste
  • Place Components
  • Reflow Solder
  • Clean Assembly
  • Apply Glue
  • Cure Glue
  • Clean Assembly
  • Wave Solder
  • Test Assembly

It usually takes several component placement steps and cleaning steps to fully complete a PCB.

There are some other unique types of custom-made surface mount components such as surface mount motors, surface mount transformers, and surface mount actuators.

These cannot be fully categorized as SMT components because their coil is printed onto the PCB itself and other main parts like ferrite core, and metal cover are soldered onto the printed board by either surface or through-hole techniques depending on required mechanical strength.

There are some other unique types of custom-made surface mount components such as surface mount motors, surface mount transformers, and surface mount actuators.

Driving forces of SMT

Surface mounting technology is driven by the advancements in memory and microprocessors.

Each new generation of memory modules and CPUs creates new types of denser and more compact surface mounting techniques.

These have thermally and electrically enhanced plastic or ceramic packages to handle a couple of hundred watts. (The Nvidia 3080 chip draws power around 300W).

Surface mount technology is also driven by continuously increasing factors like operating frequency, power, and pin count.

Another key driving factor is the real state. Modern electronics are very densely packed in such a way that mobile PCBs do not have any through-hole(TH) components anymore.

The mobile industry now totally depends on SMT.


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