SMT Assembly and Thru-Hole/Chip Functionality

Printed circuit boards are parts of various electronic devices, home appliances, and vehicles. The function of these green chips depends on their material and assembly technology. Each step of PCB assembly is important and needs careful processing considering essential features.
Two methods are popular in PCBA, including, MT and THT. Let’s study them in detail.

Through-Hole Technology (THT)

Traditional PCB has through whole technology, involving both automatic and manual processes. THT is PCB packaging technology that involves pins or leads, besides, you have to insert the chips in the PCB through holes, soldering from below. The technique gives it the name through-hole.
Through-hole technology was more in practice till 1980 and every PCB device had this technology. Then SMT emerged where chips are installed on the surface. However, some PCBs still need through-hole chips, like capacitors and resistors.
THT needs more drilling, however, the device with this technology has a durable bonding with the circuit board.
Let’s look at the important steps of THT.

Installation Of Components

Engineers place PCB components with their hands, however, it needs precision depending on the design.
PCB Inspection
PCB inspection is crucial because most devices need flawless PCBs to work well. Most of the through-hole process is manual, so you have to make sure that the assembly is without any mistakes.
Printed Circuit Board Soldering
Soldering of components is also important as you have to fix the components manually. This is the last part of assembly, and the manual work makes it more reliable than SMT.

Why Is THT Still In Use?

Though THT is an old PCBA technology, you still need it for certain reasons, such as:

• Even a hobbyist can assemble a circuit board with THT by using a soldering iron. It involves less hassle because the holes are away from surface pads compared to SMT.
• If you observe a hobbyist application of the THT circuit board, you will see the ICs with the 8 or 14-pin having centers up to 0.100”xp.300”. Sometimes even the DIP processors have such spacing between the holes that helps in manual soldering, making the PC Board assembly easier.
• After assembly, the troubleshooting or revision reduces in THT because it does not involve bridges between the pins, be it single or multiple components.
• THT has better professional assembly, especially when a project is at a prototype stage. You can apply the through holes in a prototype layout to assemble the board faster.
• After evaluating the board function, you can swap in the SMT having the same value, revising the circuit board’s layout. The new layout has small footprints to be inspected before final production. Such techniques reduce the front cost of a project which can benefit a subcontractor.

Remember that small products demand more pricing from outside vendors as they prefer high-volume production for continuous machine work.

Benefits Of Through-Hole Technology

• When it comes to PCB design revision, a through-hole technology doesn’t need to create an additional solder stencil. So, manufacturers can save a huge amount of money on a PCB design having 2 to 3 revisions before it is ready to use. Besides, you don’t have to arrange the equipment for the pick and place function.
• The manual inspection of a small lot of printed circuit boards reduces the fixture expenses or any other cost regarding linked setups.
• Soldering is also cheap in THT, such as the tin-lead solder. Besides the issue of HASL or hot air solder leveling does not occur in through-hole technology, unlike SMT where the HASL makes it hard to place the components having a precise pitch.
• You can easily assess the mechanical faults, including twists, and warps, and can deal with them while redesigning without affecting the assembly as what happens in SMT. Issues like twist and warp are not as problematic in manual assembly as in SMT.
• The hand assembly of a PCB helps fit hard components by changing the wrist angle. Whereas the automated assembly needs an extremely flat circuit board for proper functioning.
• THT can help pinpoint mechanical faults before it gets hard to resolve them. Otherwise, the inspection becomes costly when it has to go into the hands of three persons, including you, the contract assembler, and the PCB Manufacturer.
• The components for THT are easily accessible that keep the job going without interruption. Moreover, you don’t need a third-party assembly in the case of small production.
• With THT, the project timeline is predictable and easy to manage with minimum issues without causing any production delays.
• Even if you don’t want to prefer a through-hole assembly, you must consider it as a temporary solution at early stages like validation and development. So, it can benefit anyone, including a hobbyist, any established company, or a beginner in this industry.

Surface Mount Technology-Surface Mount Chip

Surface mount assembly and SMT is other popular PCB assembly technology. It is an advanced method involving automation. Besides, it is ideal for smart PCBs that today’s smart devices need.
As the name shows, PCB components are directly installed on its top surface, whereas the device having a surface mount technology is called SMD. You can say that traditional through-hole technology is being replaced by surface mount assembly.
However, through-hole technology is still in practice for big transformers or power semiconductors as their components are not compatible with SMT. Likewise, many other heavy electronic devices with heat sinks need through-hole PCBs.
Surface mount technology has more positive aspects than negative pros, so let’s discuss them in detail.

Positive Aspects Of Surface-Mount Technology

SMT Involves Minimal Surface: The component area, volume, and size in an SMT are 70% less than the component area in through-hole technology. Even the component area can become 90% less than its volume in a traditional PCB having a through-hole technology. Likewise, the overall weight of the PCB reduces, as the components’ weight reduces by 70 to 90%.
It Enhances The Signal Speed: a PCB assembled with SMT has a fast signal transmission due to a short circuit. The assembly density in such technology can go up to 5.5~20 solder joints in one square centimeter, like when there is paste on both sides of the PCB. Similarly, a PCB with SMT has a high impact and vibration resistance that helps create high-speed electronic devices.
Excellent Frequency: In SMT, the board has either no lead or it is very small which reduces its parameters, decreasing the interference in terms of RF. It means that the PCB gets high-frequency signals, and the device having it works faster.
Minimum Packaging Cost: when it comes to an SMT packaging price, you will see it much lower than THT. Since surface-mount technology involves effective production tools, the usage of packaging material reduces thus cutting down its cost. However, the decrease in the cost does not affect the quality of an SMT circuit board.
You don’t have to bend or cut the component leads in the SMT boards which reduce the assembly time, making production faster than THT. So, the production cost also reduces by 50% as the manufacturing process of SMT is quite simple.

Additional Info

In SMT, the solder paste is applied with a stencil printer that helps finish a raw board better and faster than a traditional method. In other words, you get fineness in an automated assembly.
The installation of the components becomes easier, as solder paste makes everything clear due to printing. Each SMT process is well-inspected that helps have accuracy.
In SMT, the process of reflow soldering also makes a circuit board highly durable. In reflow soldering, the technician places the circuit board under high temperature to melt and reshape the paste, making it permanent. You can use both reflow soldering and automation or can switch from one to another, depending on your needs.
The important thing is to design and assemble a PC Board considering all the dos and don’ts and have a flawless end product.

Some Negative Aspects Of SMT Assembly

Surface-mount technology is not full of benefits, instead, it has some drawbacks, such as:

• It has less power
• It is vulnerable to damage
• SMT requires high-quality soldering because poor soldering can lead to leakage, tombstoning, bridging, and several other risks.
• It involves delicate installation, resulting in dropped components.
• Its inspection is hard, especially, the visual test as it has multiple types of solder joints.
• The equipment cost is high.
• It involves well-trained technicians that increase the learning expenses.
• It needs consistent updates of assembly equipment due to fast development.

Final Thoughts

Printed circuit boards involve different assembly techniques, including a through-hole technology, and a surface-mount technology. The component area, volume, and size in an SMT are 70% less than the component area in through-hole technology.
When it comes to PCB design revision, a through-hole technology doesn’t need to create an additional solder stencil. So, manufacturers can save a huge amount of money on a PCB design having 2 to 3 revisions before it is ready to use.
Would like to know more about Surface Mount PCBs or PCB Assembly Services? Email us at sales@pnconline.com

Written by Sam Sangani

Sam Sangani is the President & CEO of PNC Inc., a Nutley, NJ based Printed Circuit Board manufacturer. Sam graduated from L. D. Engineering College with a BS Degree in Mechanical Engineering. He also continued his education and graduated from Steven’s Institute of Technology where he acquired a Master’s degree in Computer Science.

After completion of his BS, Sam worked as a QC Manager, for Xerox, Romania and London. He was responsible for the Quality Control of Cable and Wire Harness imports from Romania. After completing his Master’s Degree, he worked as a Senior Programmer with IBM, Tucson, Arizona. Sam was responsible for leading the Mainframe System Programming Team.

In 1997, Sam acquired PNC INC., a Nutley, NJ based PC Board fabrication Shop. From 1997-2013, Sam has made tremendous improvements and changes within PNC INC., as he added many new Products and Technologies in PNC’s portfolio. With his proven track record and leadership, PNC has never had an unprofitable year and has continued its growth yearly since 1997.

His current responsibilities are Strategic Planning, Corporate Management, New Business Ventures, Sales & Marketing, Trade Shows, Professional Services and leading productive teams to achieve peak potential. He has also utilized Lean Management techniques which have built a foundation for PNC’s high-paced growth. Sam also enjoys real-estate investing, web design & SEO, trading stocks, options, futures and Forex markets.