Both surface mount and through hole are the popular technological processes used in the manufacturing of Printed Circuit Boards (PCBs). They differ by the manufacturing capability and the process of placing the electronic components on the circuit board.
This article highlights the differences that exist between the surface mount technology vs through hole.
Why Do PCBs Use Process Technologies?
Process technologies like Through-Hole Technology (THT) and Surface-Mount Technology (SMT) are important for the production of circuit boards.
These processes also define the relevant steps or approaches that must be taken to facilitate the production of these boards.
When choosing one process over the other, you must consider the time constraints, cost implications and the manufacturing capabilities.
What is a Through Hole PCB?
Also spelt as “thru-hole,” the Through-Hole Technology (THT) refers to the process of drilling holes on a bare circuit board before inserting the component leads. The through hole components (the component leads) are soldered onto the bare PCB by way of hand soldering or wave soldering.
The Definition of Surface Mount PCB
The use of Surface Mount Technology (SMT) became prevalent following some of the lapses noticed in the traditional Through Hole Technology (THT).
Circuit boards built with the SMT process are usually simplified, due to the streamlined process of placing or mounting the electronic components on the board’s surface.
Why is THT not Lost in the Modernized PCB Design Process?
It is expected that since the debut of SMT in the 1980s, the use of Through Hole Technology (THT) must have faded away. However, that doesn’t appear to be happening anytime soon, as some circuit boards are still produced using this process.
But why is the thru-hole process technology still relevant till this day? Here are a few reasons why:
- It adds variety to PCB production. This is because not all the electronic components are available as Surface Mount Devices (SMDs).
- When it comes to environmental stress, THT takes the lead. It is able to withstand environment stress because of the orderly arrangement of the component leads throughout the board’s hole-paths.
The Differences between Surface Mount vs Through Hole PCB
Whether you opt for the SMT or THT processes, you need to be sure of which is the best for your electronic circuits.
Here are some of the clear differences between the two:
The Assembly Process
The method of assembling the electronic components make the two different. If you are looking for a straightforward pattern, then the SMT process is better. It is mostly automated, offering you the speed and less time spent in assembling the circuit board. But if you want varieties, go for the THT process that offers both the manual and automated assembly processes.
Likewise, the soldering process for SMT circuit boards are automated, while those of THT boards are manualized and automated.
Board Size
Real estate is a major consideration in today’s PCB manufacturing process. It is therefore imperative to choose the process technology that can fit the electronic components into the available spaces.
Surface Mount PCBs have a smaller or minimal footprint when compared to the Thru-Hole boards. In this regard, you can be sure of maximizing the available space to fit-in the components. The same is not the case with the larger THT footprint that takes up more space and could add to the buck of the circuit board’s weight.
The Dual-Sided PCBA Considerations
Two-sided or dual-sided PCBA is common with the SMDs. This is because they support the soldering of the electronic components to both sides of the board, unlike the rarity of the same in the THT circuit boards.
The Operating Temperature
The operating temperature of the laminate is another difference between the PCB through-hole vs surface mount. While the THT boards can meet up with the 130C Tg standard temperature laminate – that of the SMDs are as high as 170C Tg. This is the reason why the Surface-Mounted circuit boards are used with applications requiring higher temperatures.
The Types of Supported Components
The SMDs have more parts than the THT circuit boards. The list of SMT components includes capacitors, SOIC, Ball Grid Array (BGA), SOT, chip resistors, LCCCP, QFP, CSR and LCC.
On the other hand, the list of THT components includes lead capacitors, DIPs, lead resistors and PGAs.
The Cost-Factor
The SMT boards benefit the most when working on a budget. A couple of reasons why this is a better way to cut down on costs include:
- Dual-Sided Mounting: the two-sided mounting of the components makes the boards easier to be picked up by the machines (the pick-and-place machines). This, in turn, aids the automated process of assembling the SMD boards.
- Speed: the use of automated processes also scales the speed of producing the SMD circuit boards. That way, you spend less amounts of money paying for the extra time it could have taken.
On the other hand, using the Through-Hole Technology (THT) does not always equate to additional expenses. You might be able to save some money, thanks to the process’ non-requirement for additional solder stencil.
In this case, you don’t need to spend more money getting a new stencil for the circuit boards that are undergoing some changes.
You may also be able to save costs with the THT process technology in the following ways:
- Tin-Lead Solder Usage: as an additional cost-saving measure, consider using the tin-lead solder. It is the inexpensive variant to surface metallization and can help step-up your design process with the THT circuit boards.
- In-Circuit Testing: you also get to save money when leveraging the in-circuit testing method for THT boards. Thanks to the in-house and manual testing process, there are costs saved up from the associated setup charges and hiring of external testers for the board.
Why You May be Unable to Save Costs with SMDs
Despite the widespread claims that Surface-Mounted circuit boards are less costly, there are cases where that might not be so.
Here are some instances where the costs of assembling such boards add-up quickly:
Expensive Machinery
Due to the automated process, more expenses are underway because the pieces of equipment and machinery are quite expensive.
Additional Costs per Low-Volumes
Designing low-volumes or limited SMT boards add-up costs quickly than the mass productions.
To balance the two, the SMT circuit boards tend to become less expensive at scale, while the THT boards become more expensive, in general.
The Applicable Environment
The environment where the circuit boards are used also differentiate them. While the SMT PCBs may fall when used in high-stress areas, the THT boards are good for the high-stress environments.
Through-Hole PCB Design Advantages
If you are to go for the thru-hole process technology, here are some valid reasons to do so:
It is Designed for Higher Operating Environments
Circuit boards manufactured with the Through-Hole Technology (THT) are ideal for use in higher operating environments. This is because they form a basis for the electronic products that require interlayer connections.
Other reasons why these boards are ideal for the higher operating environments are:
- Environmental Stress: these boards are a perfect fit for the high-stress environments and they really do well in such cases. The reliability delivered to the products is because of the through-hole components that run through the holes drilled on the board. This way, they help in forming a solid connection that helps such boards withstand more environmental stresses when compared to the solders used for the SMD circuit boards.
- Interchangeability: the ability to use one of the THT components for the other is one good reason for using it. This is the reason why they make a good fit for the environments that require both functional testing and circuit board prototypes.
Larger Size
While the large size of the THT boards could translate to additional weight, it does have some advantages. For example, the larger size is a motivating factor for the application of these boards for use in the high-power applications.
Varieties in the Components
There are two major types of components or parts used with the Through-Hole Technology (THT). These are the radial lead and axial lead components.
Here is how they differentiate from one another:
Radial Lead Components
These components have the leads coming out from the component’s body. This type of protrusion is possible because of the one-sided location of the leads on the PCB parts.
The radial lead parts also have an ideal use case in the densely-packed PCBs – and this is because of the limited space they take up.
Axial Lead Components
In addition to taking up more spaces, the axial lead components have the leads running through a straightened line in the component. Other attributes include:
- The exit of the lead wire from the component on either end.
- The wires are attached to the front and back of the component.
- When the board is ready for the Through-Hole Assembly (THA); the two ends of the lead wire are placed through two separate holes drilled on the PCB. The purpose is to facilitate the flattening and proximity of the components on the board.
Downsides to the Through-Hole Technology Process
You will notice some of the following issues when using the through-hole technology for you PCB design:
Limited Routing Spaces
The length of the routing spaces is limited, no thanks to the drilling of the holes, which tends to take-up most of the board’s layers.
Time-Consumption and Increased Cost
With the support for a manualized approach, the design of THT boards takes up more time – and attracts more costs too.
For the increased time consumption, we are looking at factors like the dual-sided soldering of the boards and the restrictions placed on the accessible configuration areas for the multilayered boards.
The Hole-Drilling Procedures
Drilling or making holes on the circuit board’s surface takes a lot of time. It is also one major reason why the costs for THT circuit boards add-up quickly.
The SMT PCB Design Process
Using Surface-Mount Devices (SMDs) for your circuit boards provide a couple of benefits. In this section, you will learn about the upsides and downsides.
The Benefits of SMT Processes for PCBs
Here are some clear benefits of using the Surface Mount Technology (SMT) for your circuit board designs:
Dual-Sided Designs
You can manufacture dual-sided circuit boards, thanks to the SMT process. By allowing for the components to be mounted on both sides of the PCB, it helps to facilitate the integration of multiple parts in a denser circuit board package.
Smaller Sizes
The real estate or footprint for the SMDs are smaller and this doesn’t necessarily mean reducing the number of components used.
The smaller footprint also comes in handy for keeping the overall weight of the board within the desired limits.
Affordability
Thanks to the zero-need for hole-drilling, SMDs now cost less than the average THT circuit board.
Circuit Board Reliability
You can rely on the performance of the SMT-based PCBs. This is due to different reasons, most especially, the faster lead time and the passing of the solder joints through the reflow ovens.
Disadvantages to Surface-Mounted Circuit Boards
Take the time to evaluate the options before deciding if the SMDs are an ideal option for your PCB. Here are some of the potential downsides:
Increased Precision
More precision is required when using the Surface-Mount Technology (SMT). This is not unrelated to the fact that this process technology often has an increased complexity of the buried and blind vias used for the routing.
Unreliability for the Mechanical Stress
You are better off working with the THT process than the SMT process – that is, if you are keen on evening-out the mechanical stress.
Certain SMDs do not hold-up when exposed to mechanical stress. In that case, it doesn’t make sense to subject such components to stress that would negatively impact the performance.
Conclusion: Which is Better between Circuit Surface Mount vs Through Hole?
Both the Surface-Mount Technology (SMT) and the Through-Hole Technology (THT) provide viable means of configuring the performance of a circuit board. In some instances, it might make sense to combine the two to get the best of both worlds. Whatever your decision is, rest assured that we will help you every
