Everything You Need to Know About SMD PCB Assembly

SMD is also known as Surface Mount Device. It is an electronic device. SMT (Surface Mount Technology) is the technique that is necessary for the production of SMDs on a large scale. This modern technology replaced through-hole technology.

Through-hole technology was one of the popular ways to fit the components with wires on circuit boards. This outdated technology has many drawbacks. SMT technology is greatly helpful in mounting and soldering electronic components on printed circuit boards. Nowadays, SMT is one of the most suitable and preferred techniques to mount components on the PCB. Let’s dig deeper to learn more about PCB and SMD assembly.

What is SMD PCB assembly?

The PCB SMD assembly technique is famous for various reasons. One is its high efficiency, and the other is its wide range of uses. In the early stages, everything was manual, even SMD soldering tools. Nowadays, every modern machine has SMD PCBs at its heart. SMDs are also highly suitable for complex devices with large transformers and heat-sank power conductors.

Later some machines could only handle simple components. More Complex and small components were hard to place by machines. Now things have turned, and now every through-hole component has an equivalent form of SMD.

Through hole, assembly requires wires to connect different components on the BARE PCB. The current doesn’t flow properly in all components. This situation sometimes leads to more powerful resistance and loose circuits. The most interesting thing is that SMD components are smaller and more compact than through-hole components. It’s because SMD components don’t need wires to mount on the circuit board. It means that you can have through-hole components in a smaller size.

Steps involved in SMD assembly

These components need small pins or solder paste to mount them on PCB. Their manufacturing process is also automated nowadays. When it comes to SMD electronic assembly, SMT (Surface Mount Technology) is the most modern technique.

Electronic assembly through surface mount technology encompasses not only placing and soldering components to the PCB but also the following production steps:

  • Application of soldering paste, 
  • Placement of SMDs
  • Components arrangements on the PCB with soldering paste
  • Reflow process

To learn more about the SMD PCB assembly, let’s discuss these steps in detail.

Applying Soldering Paste

Soldering paste provides strength to the small parts on the board. Applying this adhesive paste is the first step in SMD assembly. Silkscreens help to print the soldering paste on the board. Screens are printed according to the design of the PCB board.

Different laser-cut stencils help to design custom-made screens. Soldering paste helps to solder the components on the board.

Once all boards have proper pasting of solder paste, they are transferred for assembly. Applying soldering paste is one of the first steps in the SMT assembly process. Proper application of soldering paste helps for keeping components strong and connected. It also makes sure that electrical components don’t face any resistance. It also allows integrated circuits to work properly in the device.

Components loading and placement

The electronic components’ SMDs are put in trays. Modern software ensures the proper loading of SMDs on the tray. This software also assures you that SMD parts don’t misplace. If misleading occurs, then it will ruin all PCB designs. SMT machines automatically pick one by one component from the tray and place them correctly on the military PCB.

Some SMT machines are capable of mounting more than 20000 components per hour. Once all the components are put on the board according to the design. Then the next step is strong fixing.

Affixing of components on board

Once SMDs assembling is complete, the next step is affixing the components to the board. Now it’s time to put boards in reflow ovens for soldering. These ovens have a nitrogen atmosphere, and gradual heat melts the soldering paste. This procedure results in the proper fixation of all components.

This technique of soldering is helpful for series production orders. It assures that all small components must fasten to the PCB properly. In simple words, it makes PCB fabrication easy. 

Solder paste inspection

Solder paste inspection is also necessary. Sometimes solder paste did not apply properly and evenly. So before going for placement, solder paste inspection is crucial.

If SMDs are small or highly sensitive, then a different soldering technique helps. Solder paste needs to melt according to the components. Sometimes it requires high temperatures to melt. Sometimes, low temperatures work well. Every SMD component has different soldering temperature profiles. So this technique is helpful for sensitive components. Sensitive components can melt or de-shape even at high temperatures. For this reason, using different soldering temperatures for different components is helpful.

Cooling of SMD PCBs

Once boards come out from the oven, then it is high time to cool them properly. Cooling allows solder paste to hard properly. In this way, its components stay strongly fixed on the PCB. Strong fixing of components is necessary for the proper function of the PCB boards. If components are loose, then it will affect the functioning of the board.

That is why it is necessary to cool down the soldering paste for strength. As a result, electric components stay stronger on board. Now the SMD assembly process is almost complete.

Quality check through automated optical inspection (AOI)

Quality check is very important in PCB manufacturing. No product can work efficiently without quality assurance. For this purpose, AOI is helpful. Automated optical inspection (AOI) is an automated visual inspection. AOI is helpful in detecting faults in the PCB board. Its scanning cameras automatically detect faults related to surface mounting.

It detects whether a component is missing or skewed. This system can also detect wrong-sized components on board. That’s why it is helpful in catching the right mistake in SMD assembly. The operator of the AOI machine can see the potential problem. Moreover, the AOI system not only detects the problem but also kicks out the faulty board from the series. The AOI visual check ensures consistency and accuracy in the SMT assembly production process. AOI also helps to find mount errors.

Tips for successful SMD assembly

SMD PCB assembly is a tricky process. Manufacturers have to take care of many things. Following are some key factors that are helpful in successful SMD PCB assembly.

Use suitable material

Use suitable material for connecting components. Remember one thing all materials are not suitable for SMD PCB assembly. Manufacturers mostly focus on design and make mistakes while choosing suitable materials. Materials must be suitable for connecting with pins and not affect the conductance. Sometimes materials cause hurdles in the flow of current.

Focus on the high-quality adhesive soldering paste

Solder-paste metal elements to provide its strength. Solder paste must have enough adhesive quality. If solder paste doesn’t have strong adhesive properties, then it cannot hold the small components properly. Sometimes soldering paste doesn’t melt when PCBs are put in the ovens for affixing. The low quality of the paste makes the soldering process tough.

Sometimes soldering under very high temperatures turns wrong. That is why it is necessary to discover the right materials for components and the soldering stage. There was a high need to find the right procedure and technique for fixing SMDs to printed circuit boards. Surface mount technology and soldering is the solution to this problem. Now every manufacturer is using soldering to mount components on the board. But there is still a need to develop such materials that have greeting insulating properties and high thermal resistance.

PCB SMD assembly advantages

PCB assembly is a complex process. It involves many steps. Small Electronic components are mounted to the surface of the PCB. These small components are Surface mount devices ( SMDs). SMT helps SMDs to mount properly on printed boards.

There are several advantages of using PCB SMD. Following are some advantages of SMD PCBs.

  • First, they can adjust to the small spaces due to their size. In this way, you can make complicated circuits on PCB so easily.
  • Their manufacturing is cost-effective by all means.
  • You can use double-sided boards and which allows for more component density.
  • There is less manual intervention when it comes to PCB assembly. In most cases, manual intervention is time-consuming and causes problems.
  • They made BGA assembly and PCB fabrication so
  • It was a dream to make smaller and lighter boards in the past. Now, it is possible due to SMDs and surface mount technology (SMT).
  • They helped a lot in improving the reliability of products.

Wrapping up the things

SMD assembly is only possible due to the surface mount technology. You can not imagine complex machines without this latest technology. Undoubtedly SMT is a better option as compared to the through-hole (TH) printed circuit board (PCB).

Surface mount technology makes the SMDs assembly easy and convenient. When it comes to making sophisticated PCBs with low weight, SMT comes to the rescue. PCB assembly facilitates the application of complicated devices. Enhanced automation of consumer electronics is also possible due to SMDs. I hope now you can understand the PCB assembly process properly.