The complete SMT Process and what SMT Process Engineers do in the process

Do you know how different gadgets switch between different modes when you press certain buttons? Or how you trigger certain functionalities when you touch the screen of a touch-screen device? Well, the magic behind these functionalities is known as PCBA or Print Circuit Board Assembly. Modern-day gadgets are not just simple appliances with wires and a few functionalities. Modern-day gadgets have become helpers due to their outstanding capabilities and their compactness. PCBA brings together various electronic components onto a pretty small area; hence they achieve compactness. The parts, though minute, match or even outdo similar but larger traditional components. They are thus more productive too. But how does PCBA achieve this? Well, it achieves this through a process known as an SMT process. But what does the SMT process entail? And what exactly is SMT?

SMT

SMT stands for surface mount tech. It is a new method that manufacturers utilize to mount electronic components on print circuit boards.

Basically, SMT involves the soldering of SMCs (surface mount components) onto PCBs via reflow soldering.

SMT Process

Material Examination and Preparation

In this step, the manufacturer prepares the PCB and SMC and checks for flaws in both of them. The Print Circuit Board mostly has flat gold plated copper, silver, or tiny-lead pads which have no holes. These pads go by the name solder pads and are crucial in the SMT Process.

Stencil Preparation

The Stencil provides a fixed solder paste printing position. The design of the Stencil perfectly matches the solder pad’s positions on the PCB. In doing so, it makes mounting pretty easy to accomplish.

Solder Paste Printing

The Solder Paste in these steps is a mixture of:

• Tin
• Flux

The solder paste attaches surface mount components onto solder pads according to specifications. Then, a stencil utilizing a squeegee at an angle of 45⁰ to 60⁰ applies the solder paste onto the PCB board.

SMC Placement

Now it is time to mount electrical components onto the PCB. Manufacturers utilize a pick and place machine for this process. The machine accurately mounts SMCs onto the board accordingly. Once the mounting process is over, the PCB moves on to the reflow soldering process.

Reflow Soldering

• Soldering oven – When the surface mounting process is over, the PCB enters a reflow soldering oven.
• Preheat zone – The very first zone inside the reflow oven is the preheat zone. In this zone, the board’s temperature plus that of all the components attached to it raises gradually and simultaneously. The rate of temperature ramp-up in this zone is about 1⁰C to 2⁰C per second up until it hits 140⁰C to 160⁰C.
• The soak zone – The PCB remains in this zone for about 90 seconds on temperatures ranging between 140⁰C to 160⁰C
• Reflow zone – The PCB then goes inside a section that has a temperature ramp-up of 1⁰C to 2⁰C per second. The temperature gradually goes up till it hits a temperature range of 210⁰C to 230⁰C. Once the reflow zone hits this high temperatures, the tin found inside soldering pastes starts to melt. The molten solder binds the SMC’s leads onto the PCB’s pads. The molten solder’s surface tension helps keep the SMCs in place.
• The cooling Zone – a zone that makes sure the solder paste freezes as it exits the heating zone. By passing through this zone, the print circuit board avoids any joint defects.

In case the PCB is double side you might have to repeat this entire process using glue or solder paste to hold the SMCs in place.

Cleaning and Inspection

The PCB cleaning process after soldering is pretty essential. Once the cleaning process is over, the operators check for flaws in the PCB. If any defect is found, then they have to repair or rework the defect before storing it.

Standard machines that come in handy during this entire process include:

• Automated Optical Inspection
• Magnifying Lens
• Flying probe tester
• X-Ray Machine

SMT Process Engineers, what do they actually do?

SMT Process engineers come in handy when:

• A confusing issue arises during the PCB assembly process
• The rejection rate declines miraculously or
• PCB assembly products drop in terms of manufacturing efficiency and quality

SMT process engineers have the following responsibilities:

• They deal with abnormalities that occur during the PCB assembly process
• The SMT assembly process plus how to efficiently upgrade it
• They decrease the rejection rate and improve the pass rate
• Testifying and implementing unique strategies for manufacturing purposes
• Setting the process parameters
• They evaluate new methods and new components

Briefly put, we can say that an SMT process engineer prepares, implements, and then monitors the entire SMT process.

Since technology advances, so does the responsibilities of SMT process engineers. However, any additional role has to align with a particular tech advancement to cope with the increasing market demand.

Some Non-academic Skills that you require to become an SMT Process Engineer

Firstly, you should have the ability to predict and define possible results that might occur due to process changes. Immediately a change occurs in the SMT process. You should have enough sensitivity to accurately predict the corresponding results. Using this predictions, manufacturers can make a timely changes to affect other processes positively.

Secondly, you should know every tool that helps execute the SMT assembly process. Competition in the electronic market as per the 21^st century is pretty tough. Clients now require devices of high quality and at an affordable price. The only companies that can afford this feat at those that utilize efficient tools. Therefore, SMT process engineers should have proper knowledge of SMT process tools, how they work, and any advances of the same. SMT process engineers should greatly embrace development.

Significance of SMT process Engineers

• The SMT process features so many elements such as:
• Component package
• Technical requirements
• Materials
• Equipment et cetera

Hence there should be someone who can easily understand, explain and also monitor the entire process.

• Companies worldwide are under constant pressure to improve on quality to match higher quality products. The competition is pretty intense, and those who lose ultimately go under. Also, when it comes to optimizing the SMT process, manufacturers highly depend upon SMT engineers. They help them produce electronic gadgets in bulk using less money, improving their profit margin.

Conclusion

The need for SMT assembly grows every day. Clients want gadgets that are:

• Compact
• Fast
• Efficient
• Cost friendly

With SMT processes, manufacturers can achieve this feat. However, due to technological advancements, this needs gradually change. For example, clients now want a faster component with better battery life. Hence we have SMT engineers. These engineers help manufacturers cope with the current market. They help them produce quality each time using minimum resources. Therefore the next time you see a company launch a device update that might be thanks to a certain SMT process engineer.