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What is Through-Hole Technology?

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Published by Pinsheng Electronics Co., Ltd February 20,2020

What is Through-Hole Technology?

Through-hole technology or through-hole assembly, means a method to assemble the electronic components to the PCB board. Comes to through-hole technology, the components' pins are plugged into the through-holes from the topside of a PCB board, then get soldered onto the pads on the bottom side.

Through-hole technology

Through-hole technology became a PCB assembly standard in the 40s, now it is still in use. Early through-hole assembly was covered by handly plugin and soldering, while today, most of the work can be finished by automatic machines.

Placement machine

 

There are normally two types of through-hole technology:

1.Axial
The metal wire crosses the body of component axially, two long pins lead out from two sides. This kind of parts will not take too much axial spacing, and good for flat assembly request.

axial parts for through-hole technology

2.Radial

Two short pins lead out from the same side of a component, which means this component will stand out from the board surface while saving axial spacing, good for dense assembly. 

radial parts for through-hole technology

 

The Advantages of Through-Hole Technology 

  • Through-hole technology makes the connection more reliable. In through-hole assembly, the pins can go through all the layers of the board, while has higher mechanical strength. It is suitable for larger or heavier parts, as well as sockets, connectors that need to be reinforced.

  • Through-hole assembly generally can withstand higher thermal shocks, so often used in military and aerospace applications.

  • Through-hole technology is ideal for prototyping and testing because components on the board can be easily replaced.

Although SMT technology has become the mainstream, through-hole technology is still irreplaceable because of its above characteristics.

 

The Disadvantages of Through-Hole Technology 

Through-hole technology was almost replaced by SMT technology because its shortcomings are also quite obvious.

  • Firstly, through-hole technology needs additional drilling to make the board more costly to produce.

  • Secondary, these larger through holes occupy a lot of spacing on the PCB surface, which limits the circuit design.

  • Moreover, electronics are becoming more and more sophisticated, the huge components of through-hole technology occupy a large amount of the spacing, which is undoubtedly unsuitable for high-density and small-sized designs, meanwhile smaller size means lower manufacturing costs, SMT technology has great advantages in this respect.

 

The Basic Flow of Through-Hole Assembly

No matter which method is used, through-hole technology or SMT technology, both of them must meet the soldering standards, the processes of them are basically the same:

  1. Manufacture the required PCB board (Single or Panel)
  2. Pick-n-Place (Automatic or Manual)
  3. Soldering (Reflow or Wave Soldering)
  4. Inspection (X-ray, AOI, Visual)
  5. Cleaning (Ultrasonic/Water-based Cleaning)
  6. Breakaway (For Panel)
  7. Testing (ICT, FCT...)

The difference is mainly in the placement of components and soldering. 

So how to determine whether to use through-hole assembly or SMT assembly at the design stage? The following are general guidelines.

through-hole assembly or SMT assembly

Of course, it must also be involved in different products and application environments to meet product availability and manufacturability.

 

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