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SMT Assembly – What Should You Know About it?

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What Should You Know About SMT Assembly?

The PCB industry used to fabricate boards by using the through-hole approach during the mounting phase. However, the companies have adopted the new SMT approach, which proved to deliver a better outcome and be more efficient.

The SMT stands for surface-mount technology. The idea was to eliminate the requirement that the leads of the components go through the PCB. The alternative suggested was to solder the elements, and that turned out to be an improved solution.

The SMT assembly procedure enhanced over time, and it is the primary approach to PCB fabrication today. You can use boards manufactured this way throughout all electronic industries. The chances are you will find them in smartphones, computers, refrigerators, TVs, etc.

Uses for Surface Mount Technology

This technology comes in handy when designing compact products that maintain high performance or processing power. 

So, you should consider surface-mount devices when you need high-density boards that are compact, lightweight, and powerful.

You should also consider this tech if you want electronic products with reduced noise in high-speed, high-frequency applications or when you want to automate the manufacturing and assembly process for mass production.

Surface-mount component reels feeding a pick-and-place machine during SMT assembly

Surface-mount component reels feeding a pick-and-place machine during SMT assembly

With these factors in mind, SMT is ideal in the following areas.

  • Telecommunication equipment (mobile devices)
  • Consumer electronics
  • Defense, aviation, and aerospace devices
  • Industrial control systems
  • Medical equipment

Surface mount technology (SMT) has become the primary approach used in the process of designing and fabricating PCBs. The technology is reliable and delivers consistent results, which is the reason for its popularity in the electronics industry.

In this article, we will explain the details of the SMT assembly procedure. You will also learn more about the current development trends and the future of the SMT industry.

 

A printed circuit board with letters flexible over it

The Benefits of SMT Assembly

The surface-mount technology requires familiarity with the entire process. It has specific demands for the design phase as you need to use special PCB tools. Once the design is ready, the manufacturer will do the testing with a single board.

The prototype has the task of confirming that the fabrication based on that design is possible and error-free. Once you confirm that, the entire process is virtually automated and requires minimal involvement. The only thing needed is the right machines that can meet the challenge of fabricating the particular PCB.

Thanks to that automation, SMT assembly minimizes errors that may happen due to human involvement. It secures improved reliability and consistency of the boards. Here are some other advantages that this approach ensures:

  • Reduced size and weight – by soldering components directly on the board, the SMT saves plenty of room. That is how you can maintain the reliability and performance of a PCB while reducing its size and weight.
  • More components in a smaller space – it is not only about reducing the size, but SMT also enables us to put more elements in a restricted area. That is how these boards can perform better than their predecessors while keeping their compact design.
  • Money savings – if you don’t use the same amount of materials as before, the cost should be decreased, too. Additionally, there is no need to go through hole-drilling operations to mount components. Thanks to that, you can also lower the labor costs.

Disadvantages of SMT Assembly

Although the compact, lightweight, and powerful design of SMT devices gives them several advantages, the assembly process has some drawbacks, which include the following.

Unreliability

The limited solder used to attach surface-mount devices to the pads can fail if the PCB gets exposed to environmental, temperature, and mechanical stresses regularly. As such, the components and the board will be unreliable during operation.

Surface-mount devices soldered on a blue PCB

Surface-mount devices soldered on a blue PCB

But instead of switching to through-hole components for the entire board, you can mix the two technologies to get both benefits. More on that later.

Difficult Maintenance

The Surface-mount components are tiny, which makes parts identification on the board, component value identification, repairs, and reworking challenging. Miniaturization also complicates the board inspection process.

Soldering Issues

Some SMT devices are sensitive to high temperatures during soldering and can experience permanent damage if you’re not keen.

Therefore, it might be impossible to mass-produce boards with components that cannot withstand the high heat levels during reflow soldering.

Delicate Components

The miniature size of surface-mount devices makes them easy to drop, especially if assembling the board manually. And when you drop them, the parts get damaged easily.

High Investment Costs

As an assembler, you need a high initial investment cost to purchase equipment and train workers to handle SMT assembly.

SMT Accembly Process—Component Placement

The first part of the procedure we will discuss is component placement. It may seem like a basic step of the process, but it is essential. The reason for that because you need to mount the components on the printed circuit board properly.

The designing process must be error-free. Since the fabrication will merely follow the commands received in the design, that is how you ensure everything goes smoothly.

The task of the designer is to assess the position carefully. The idea is to have the production phase in mind when placing the components. The current manufacturing capabilities need to be capable of meeting the expectations. If that is not possible, the manufacturer might be unable to print the parts, which will automatically discard the PCB, and return the entire process to the beginning.

The experts recommend starting the component writing with simple structures. Once you complete that part, you can move on to those parts that have a complex structure chip type.

Image 3: An engineer checks a PCB for potential errors

SMT Accembly Process—SMT Printing

First, let’s clarify what do we refer to when we mention SMT printing. The process involves the solder paste added to the pads of the board, which involves screen printing that doesn’t require direct contact, as well as contact stencil printing. The specifics of the SMT assembly imply that this technology requires screen printing that belongs to the contact type.

Everything starts by stirring the paste for soldering. You must keep in mind the uniformity and viscosity of the paste while you are getting in ready. As for the viscosity, it may affect the printing quality significantly. The idea is to follow the current printing standard and adhere to its requirements. You don’t want the viscosity to be far from the recommended range because you may disrupt the printing quality.

You will need to store the paste in a suitable environment, too. The industry experts recommend keeping the temperature low. The ideal temperature range goes from 0 to 5C. The reason why is that the segments of the paste can separate naturally in those conditions.

Now, when you plan to use the paste, you should take it out of the fridge and allow it to rest at room temperature. Give it about 20-30 minutes to heat naturally, and use a glass rod to stir it. It will take about 15 minutes of stirring to get the paste ready for use.

You should aim to keep the optimal room temperature while using the paste. That means the heat range should be between 20C and 25C. Another important factor to consider is humidity because too much humidity may affect the paste. That is why you should give your best to keep it around 50%.

Once you apply the paste to the pad, they will become an integral part of the SMT assembly. That is because they are an essential requirement for component soldering.

Here is what happens during the printing phase – the pressure of the blade will spread the paste throughout the pad. Next, the stencil’s thickness will keep at up to 0.15mm for optimal results. It is interesting to mention that the industry experts believe the silkscreen paste for soldering makes the paste fuller and improves the quality of the soldering.

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SMT Accembly Process—Reflow Soldering Process

The next step in the SMT assembly procedure is the reflow soldering process. However, before we go into this phase, it is vital to assess the component position and orientation one more time.

In the reflow soldering phase, you want to maintain optimal temperatures. Since the phase will involve welding, you should be aware of the parts of the work, and these are:

  1. Preheating – the idea of this phase it to confirm that you achieved a stable and balanced temperature of around 180C. It is vital to keep the temperature of this range without straying too much. As for the humidity, try to maintain it at around 50%.
  2. Heating – the heat should be around 245C. Now, the vital thing to consider is that the solder paste can melt in 183C.
  3. Cooling – the cooling process involves slowly cooling down the temperature of your board. That is vital to achieve optimal results and prevent extreme temperature changes to affect the PCB.

SMT vs. THT: Which To Choose

SMT is more space efficient because the devices are tiny. It can also be cheaper because you don’t have to drill mounting holes through the PCB. However, the technology offers limited mechanical strength to secure the devices to the circuitry.

Therefore, you can only use SMT to attach lightweight components like transistors, resistors, and integrated circuits to the PCB.

THT takes up more real estate on the board, but soldering the lead through the board creates a solid footing that can withstand mechanical, thermal, and electrical stresses.

A PCB with multiple through-hole components

A PCB with multiple through-hole components

So, this technology is suitable for mounting components like connectors, transformers, and inductors, which need a solid footing to remain reliable.

SMD vs. SMT: What Is the Difference Between SMT and SMD?

SMT is a technology that welds leadless and short-leaded components to PCB pads using solder paste printing and reflow soldering processes. These processes allow manufacturers to automate PCB assembly, which enables mass production.

On the other hand, SMD refers to surface-mount devices, which are the electronic components you mount to PCBs using the SMT process. These devices are mostly leadless, but some can have short leads that don’t go through the boards. These are typical in some IC packages.

Multiple surface mount devices

Multiple surface mount devices

The primary goal of using SMT is to enable precise installation and automation, while the main objective of SMD is to allow miniaturization and high-density assembly, especially on multilayer PCBs.

SMT IC Package Types

These package types can fall into two categories, which are leaded and leadless. Leaded IC packages include the following.

An integrated circuit with a quad-flat package 

An integrated circuit with a quad-flat package

Typical leadless IC packages include the following.

  • Small Outline Non-Leaded Package (SON)
  • Quad Flat Non-Leaded Package (QFN)
  • Land Grid Array (LGA)

Ball Grid Array (BGA)

Development Trends and the Future of SMT

We already established that the SMT assembly has become a prevalent method in the PCB industry. It doesn’t come as strange that the majority of manufacturers have jumped on board and adopted this technology. It is a trend that will continue in the following years as SMT has become the dominant way of fabricating printed circuit boards.

The users are those who will benefit the most from the competition getting fierce. At the moment, the cost of a PCB designed by using SMT is not negligible. However, the manufacturers will keep aiming to offer more affordable prices and better service than the competition. As a result, the users can expect to receive top-class boards at budget-friendly rates.

We already see the progress in the SMT industry. The automation is at a high level, and the companies are trying to offer excellent logistics. Technological progress inevitably makes everything more accessible, and that includes SMT.

If you compare the current situation to the last several years, you will notice the development process significantly improved. Additionally, the cost of the components and labor are now smaller, and the boards can be adjusted to suit every customer and application.

Future trends in the industry are quite obvious. The experts will continue to find ways to improve the flexibility of the boards while keeping them reliable. Additionally, the industry will have to consider environmental factors, as well as ease of use.

What Is an SMT Assembler?

An SMT assembler is a facility that offers surface-mount device mounting solutions. This facility should have the required equipment to handle these tiny SMDs and trained operators to handle the machines and the entire process.

A fully automated SMT assembly line in a production facility

A fully automated SMT assembly line in a production facility

How to Choose the Best SMT Assembler/PCB Manufacturer

Whatever your application is, you want a printed circuit board that will perform well and maintain reliability over a long time. That is something you can achieve if you have a trustworthy manufacturer by your side.

OurPCB has years of experience in fabricating printed circuit boards. Here is what the company offers to its clients:

  • Modern equipment – the factory has state-of-the-art tools that can meet the challenges of building even the most complex PCBs.
  • Experienced engineers – a team that is ready to help you throughout the entire process and ensure everything goes smoothly.
  • Top-quality materials – the company only uses high-quality materials so that the quality of the boards can meet and exceed the user’s expectations.
  • On-time delivery – the manufacturer is capable of meeting mass-production requests in the shortest possible timeframe. The company guarantees production completing within the specified deadline.
  • Affordable rates – the customer is the priority concern for the company. That is why you can expect affordable prices that meet any budget.

Conclusion

The SMT assembly is taking the throne when it comes to PCB fabricating. The industry concluded that it is an efficient and reliable way of designing printed circuit boards.

We can only expect the entire assembly procedure to improve in the future. Even today, customers can expect reliable boards at affordable rates. However, it is essential to work with a trustworthy manufacturer with the necessary experience and equipment to meet the needs of your specific PCB.

Special Offer: Get $100 off your order!

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Please email [email protected] for details.