The process of launching a new electronic product in the market is a decision-making process that entails thousands of decisions. You are forced to choose the parts, create the housing, and code the program. Nonetheless, one of the most critical decisions to make occurs before a single part is soldered which includes the correct selection of the printed circuit board or PCB assembly method.

The assembly approach that you employ will determine the size of your product, its cost, durability and the speed at which it can be manufactured. Make a right choice and you open the road to large-scale profitable production. Make a wrong choice, and you can spend much money on rework or even failures in the field.

There are two main PCB assembly methods, as Surface Mount Technology (SMT) and Through-Hole Technology (THT), which are mainly used in the industry. This is a breakdown of how they operate and how to arrive at the right one that is suitable in your particular project.

Surface Mount Technology or SMT

Surface Mount Technology is the prevailing technology in the current electronic manufacturing. Imagine opening a smartphone or a laptop, nearly all the things that are inside it were put together using SMT.

Here, the elements are attached to PCB surface. The board is covered with solder paste by stencil, the components are positioned with high precision with the help of a pick-and-place machine and the board is placed in a reflow oven to melt all the solder and form permanent electrical connections.

When to choose SMT

The preferred option of high-volume production and high-density, intricate designs is SMT.

• Miniaturization: The SMT components can be infinitely miniaturized. SMT is necessary in case your phone must be put in your pocket or on your wrist.
• Automation and Speed: It is much automated. Large batches are costly to produce in terms of labor and time but tens of thousands of components can be placed by machines in an hour, drastically lowering these costs and time.
• Cost Efficiency: Due to the space reduction of SMT parts and the speed of the process, the unit cost reduces greatly due to the increase in volume.

Limitations

Inasmuch as SMT is effective, solder connections are not as mechanically sound as through-hole connections. They can be inappropriate with heavy components or parts that experience severe mechanical forces, e.g. large connectors.

Through-Hole Technology or THT

The years preceding the introduction of SMT as the standard in 1980s had the Through-Hole Technology as the reigning technology. Under this approach, leads of components are pushed through holes that have been drilled on the PCB. The leads may then be hand soldered or an equipment wave soldering machine can be used.

Although it may look old fashioned as compared to SMT, through-hole still has its role to play in certain situations where durability is not negotiable.

When to choose THT

The THT should be taken into consideration when your product must be able to work in extreme conditions or when it must be very strong in mechanical characteristics.

• Durability: The leads that are passed through the board offer a substantially better physical connection than surface mounting. This is essential to elements that the user has physical contact with such as switches, connectors and input/output ports.
• Large Power and Heat: THT components are generally larger and can support higher loads of power and thermal loads more than the tiny SMT counterparts.
• Prototyping & Testing: It is easier to make manual adjustments in THT. THT is much more user-friendly in case you are in the early R&D phase and you have to change capacitors or resistors manually.

Limitations

THT involves drilling holes on the board, thereby making the bare PCB more expensive. It also restricts signal trace routing areas of multilayer boards. Moreover, it is typically slower and more difficult to automate the whole assembly process than the SMT.

Things to think about with your business

Ideally, you will not be forced to make a decision on only one of them. A large number of intricate assemblies combine a hybrid solution, with most components being done in SMT to reduce space and cost, but with certain connectors or power components where additional strength is needed done in THT.

These three factors need to be evaluated to come up with the final decision:

• Volume of Production: In the case of 10,000 units that an individual is producing, the SMT automation is necessary financially. When you have a production of 50 custom units in the aerospace industry, it may be preferred that the THT manual reliability is used.
• Product Environment: Will the device be exposed to vibration, shock or excessive heat? In that case, THT is reliable enough. SMT is quite suitable to standard office or home conditions.
• Board Real Estate: SMT enables you to mount the components of both sides of the board densely in the event that space is limited. THT occupies much larger space.

Conclusion

Finally, the correct method would be based on the needs of your application. Majority of the consumer electronics will be heavily dependent on SMT due to its low prices and small size. Nonetheless, through-hole Technology is likely to remain relevant in decades to come as far as industrial, military and aerospace application is concerned.

It is always better to involve your electronics manufacturing partner at an early stage of the design. They are able to examine your Bill of Materials (BOM) and intended use case to advise you on a PCB assembly strategy that would be cost effective, fast, and reliable.

Optima Technology is a PCB assembly partner you can count on.