Difference in Through-hole and Surface-mount Technology in Printed Circuit Boards Assembly Line

The Difference Between Through-hole Technology and Surface-mount Technology in PCB Assembly Line

The printed circuit boards are integral to all modern electronic devices. Have you ever wondered how these complex tiny circuits are assembled? Depending upon the complexity of the circuit, PCBs are divided into three types, primarily:

  1. Single Layered: the components are mounted on to one side of the board. These are the most commonly used circuit boards.

  1. Double Layered: when the components are mounted on either side of the board, a double layered PCB is formed.

  1. Multi-Layered: when there are more than two layers of PCBs combined together, with each layer mounted with its own set of components, a multi-layered PCB is formed.

The PCBs, after construction and fusion of layers, are assembled with different components to functionalize the circuit boards. The leading manufacturer of PCBs, mjsdesign.com, tells us that there are primarily two technologies employed for PCB assembly. The first one being Surface-Mount and the second, Through-Hole technology. The former one is used where only one side of the board is to be mounted with components whereas, the latter being used for multi-layered PCBs. Let us get a brief knowledge about how these two technologies are different:

1. Stenciling the solder paste

For single layered circuit boards, there are lesser complexities involved. The top layer of any PCB is coated with a thin film of solder paste. This solder paste allows the mounting of components on the surface of the board. Whereas, there is a limitation when it comes to the through-hole components.

2. Mounting the components

The components which are to be mounted on the surface can easily be mounted, but when it comes to the through-hole components the task becomes a little tricky. Through-hole components are primarily used to pass on signals between two or more layers of the PCB. Ordinary soldering proves drastic when mounting such components. Any unnecessary solder bridges can alter the performance of the circuit and render the board as scrap.

3. Reflow soldering / Wave Soldering

Another difference between the two technologies can be observed in the type of soldering method employed. In SMT, ordinary soldering can suffice the purpose but in THT ordinary soldering may render the circuit boards scrap, as already mentioned. The different approach in soldering through-hole components is accomplished by wave soldering. The holes in the board are filled with solder paste and the component is mounted on. The solder paste is not simply poured into the holes but rather plated over the edges to make the impregnation precise.

4. Inspection and quality control

Finally, at every step of the assembly line, the boards are inspected and checked for quality purpose. The electro mechanical assembly line of PCB may involve a number of quality checks, during and after the assembly process is over. Both the technologies make use of one of the three methods prominently used for inspection: visual inspection, optical-mechanical inspection, and x-ray inspection. Depending upon the company standards, a faulty board may either be reprocessed or scrapped.

After the assembly process is complete, each board is cleaned in a thorough bath of chemicals. Later they are checked and tested for their performance.

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