SMT or Surface Mount Technology Explained

by | Apr 2, 2019 | 0 comments

While the world, including us, keeps showing-off about PCBs, we tend not to talk about PCB components because they are quite complex. Today, we thought we could explore complex topics while trying to have fun. So, let’s start with surface mount technology (SMT).

“Every once in a while, a new technology, an old problem, and a big idea turn into an innovation.” -Dean Kamen, American engineer, inventor, and businessman.

Gadget users always have a constant set of demands, sleeker products, and faster operations. In the electronics industry, SMT has largely replaced the through-hole technology construction method of fitting components. Why?

Because an SMT component is usually smaller than its through-hole counterpart. It has either smaller leads or no leads at all.

Before we can dive into surface mount technology, its applications and more, let’s take some time to look back at its history.

What is surface mount technology?

And how did it come into existence?

During the 1970s and 1980s, the automation level in the construction of electronic equipment gained momentum. Soon traditional components with leads started becoming difficult to handle. Resistors and capacitors required to have their leads pre-formed so that they would fit through holes. Even integrated circuits needed to have their leads set to exactly the right pitch. PCB technology doesn’t really require the component leads to pass through the board. Instead, soldering components directly to the board is quite adequate. Therefore, surface mount technology was born. And very soon we found ourselves completely engulfed by SMTs. Now, we use the main technology we use for electronics manufacturing.

The differences between through-hole and surface mount technology:

  • SMT components are usually more cost-effective than their through-hole counterparts.
  • SMT takes care of the space problems that are common to through-hole mounting.
  • In SMT, components are directly mounted to the PCB, whereas through-hole components require lead wires that pass through drilled holes.
  • The pin count is higher in SMT than in through-hole technology.
  • SMT readily acquire higher speed in circuits because of its reduced size.
  • SMT demands a higher quality of design, production, skill, and technology.
  • As components in SMT are more compact, the packing density is also much higher than in through-hole mounting.

Use of SMT is common now in most of the commercially manufactured equipment. That’s because it offers significant advantages during manufacturing. Even if we consider the size aspect, the use of SMT components enables way more electronics to be packed into a much smaller space.

In addition to the size, this brings significant improvements in reliability. SMT typically allows automated production and soldering use. We employ SMT because it speeds up the production process. On the other hand, the risk of defects also increases due to component curtailing and the denser packing of boards. In such conditions, detection of failure becomes critical for any SMT manufacturing process. In that case, the through-hole process again comes into existence.

However, both surface mount technology and through-hole can be utilized on the same PCB. This is because there are some components that simply do not cooperate with surface mounting. These components might include large transformers and heat-sinking power semiconductors.

As of now, this is clear to us like any other new technology, SMT also comes with a few advantages as well as disadvantages. As we know, there is always a flip side of stardom. Let’s discuss its good side as well as the flip side.

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Advantages of surface mount technology:

The basic advantage of SMT is obviously the size. As we have already discussed in all our previous articles, the market demands sleeker, smaller and yet faster devices. SMT is making this possible. These units are not as heavy as the previous units. But there is actually a much higher component density, as well as more connections per each component. Therefore, we can conclude that surface mount technology is way more efficient and advanced than any technology ever before, while it is absolutely compact. We do not drill a lot of holes into the board. This leads to faster and more automated assembly processes.

Since components can be placed on either side of the circuit board, it simplifies things further. And to top this, some SMT components and parts actually cost a lot less. Consequentially, we have a lower initial cost, less time required for setting up and production, and a reduced manufacturing cost. That comes as an efficient use of time and money. Virtually, it nullifies any sort of electrical noise in the device. But in the real world, it reduces the noise to a maximum extent. The SMT component weighs almost as little as one-tenth of their common through-hole equivalents.

Now, you must have heard a fact. A fact that tells surface mount technology is accessible to both design and development. That can be a little tricky to understand.

Advantages of SMT based on design:

  • Significant reduction in weight and real estate as well as electrical noise reduction.

Advantages of SMT based on development or manufacturing:

  • Reduced board costs.
  • Reduced material handling costs.
  • Controlled manufacturing process.

Disadvantages of surface mount technology:

Fortunately, there is always room for improvement. Hence, there is nothing called a full-proofed manufacturing process. Therefore, SMT has its share of problems as well. For any large, high-power/voltage parts SMT is not really ideal. This is why we sometimes incorporate both the contemporaries together, i.e., through-hole and SMT on the same device. The small lead spaces can make repairs more difficult. It does not guarantee the solder connections. Whether they can withstand the compounds used during potting application. The connections may or may not be damaged when going through thermal cycling. Components that generate a lot of heat or bear a high electrical load are not suitable for SMT because the solder can melt under high heat. The solder is not really adaptive to mechanical stress. This means components that will be directly interacting with a user should be attached using the physical through-hole method.

Now, an important question is when should we use surface mount technology?

Because its new, the majority of products manufactured at this time utilize surface mount technology. But SMT is not suitable in all cases. As a rule, SMT should be considered if:

  • You need a compact or small product.
  • Your need is a monstrous mind, i.e., the device should accommodate large volumes of memory.
  • Your final product needs to be sleek and light despite component density.
  • You need high-speed/frequency functioning of the device.
  • You need to produce large quantities with automated technology.
  • Your product should produce very little noise (if any at all).
  • Your product must accommodate a large amount of high lead-count complex ICs.

The differences between SMT and SMD:

While we have almost reached our conclusion, let’s discuss something that’s still bothering you. We came across two terms in this article: SMT and SMD. These two little acronyms can topsy-turvy the entire electronics manufacturing service world, if not dealt properly. On paper, they only vary by a single letter. However, in practice, there’s a lot distinguishing SMTs and SMDs. For starters, one is a process and the other is a device.

Small components attached to boards in electronics manufacturing are surface mount device (SMD). Their design also fulfills the same smaller and faster demands. Therefore, they are smaller than their previous devices. SMDs were created to use with the highly-efficient and precise SMT.

But SMD and SMT do combine at some point.

In the early years of SMDs, these smaller and more complex components were placed and soldered by hand. Machines could be used but were limited to size and type. Today, manufacturing boards using SMT is nearly the same, but much faster and far more precise.

Back then, we used small bits of silver or lead to attach the component. We still use the same elements but in a solder paste. SMT machines can attach thousands of SMDs per hour, compared to maybe a few hundred by hand. As a result, approximately every through-hole process now has an SMT equivalent.

The SMDs became popular in response to SMT efficiency of producing boards. Therefore, their combination basically referred to an efficient use of both time and space. SMD meant that more could be done with a smaller, more accurate devise. So, SMT could assemble them in a jiffy and with more precision possible than ever before. The cost savings when they were combined consequently had more and more electronics manufacturing services combining SMT and SMDs.


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