A Guide To Through Hole Assembly & How It’s Used

Through-Hole Assembly is a process where component leads are inserted through pre-drilled holes in printed circuit boards and soldered from the other side. Traditional or conventional methods of assembly are classic, tracing their roots back to the very beginning of electronics manufacturing when electronics could be assembled onto simple material of printed circuit board material. Traditional methods of assembly, which date back to the very beginning of electronics manufacturing, remain key to many applications today.

This article aims to act as a guide to Through Hole Assembly and how it is used:

Through Hole Assembly – The Basics

Components in through-hole assembly with wire leads or pins are designed to fit into pre-drilled holes in the circuit board. These holes, most of the time plated with conductive material, create electrical connections between the component leads and the conductive traces on the PCB. These then get soldered onto the bottom side of the board after insertion, making both mechanical and electrical connections.

Through Hole Assembly – The Process

Generally, THA involves a large count of electronic components-from ICs in DIP packages to electrolytic capacitors, larger resistors, transformers, connectors, and power elements. This method is preferred for components that could be subjected to mechanical stress or require stronger physical attachment to the board. The major steps this process involves are the preparation of the PCB, with accurately drilled holes matching the spacing of the component leads. After the insertion of components, the leads that normally come from the bottom of the board are slightly bent to hold the component in place as it goes into the soldering process. Clinching is a process that avoids parts falling out when the board is generally moved around or inverted. It then passes under the soldering stage, which can be done in several ways: wave soldering, selective soldering, or even hand soldering.

Through Hole Assembly – The Pro’s and Con’s of Use

One of the key benefits that through-hole assembly provides is mechanical strength in the connections. The physical attachment by passing component leads through the board and soldering provides excellent stability, and THA is thus accordingly very well fitted to products likely to be subjected to vibration, physical stress, and frequent handling. This makes it particularly suitable for automotive applications, industrial equipment, and military hardware. Through-hole assembly also provides several advantages in component replacement and rework. Due to the fact that the components are soldered individually and accessible from either side of the board, they can be relatively easily desoldered and replaced if need be. This makes the through-hole assemblies generally more serviceable and repairable compared to surface mount technology in many applications.

However, there are a few shortcomings with through-hole assembly. The process generally requires more PCB real estate than in surface mount technology because holes must be drilled through the entire board, thus reducing routing space on all layers. Such drilling increases the cost and complicates the fabrication of PCB. Lastly, usually the assembly process is slower than SMT, since components have to be inserted one at a time and soldering is more time-consuming and requires more material.

Through Hole Assembly – Facts to Keep in Mind

Through-hole assembly is highly dependent on the proper soldering technique. A good solder joint should look concave and smooth, with the solder wicking up the component lead to make a secure connection to the pad. Common defects include insufficient solder, excessive solder, cold joints, and voids. However, regular inspection and quality control measures will rule out these errors in time. In today’s electronics manufacturing, a through hole is often combined with surface mount technology. This hybrid technique enables designers to exploit the advantages of both approaches: designers use SMT for the majority of components to obtain high density and efficiency and use through-hole assembly for the components that require higher mechanical strength or are available only in through-hole packages.

Conclusion

Despite the rising use of surface mount technology, through-hole assembly continues to be one of the major manufacturing processes in electronic industries. It offers an alternative option for those particular applications where mechanical strength, power-handling capability, or serviceability is an issue. This technique also finds wide application during prototype development and small-scale production due to the great convenience of manually assembling and modifying circuits. Overall,  through-hole assembly is retaining its place as a viable and practical method of assembly in this fast-developing world of electronics manufacturing. Through-hole mounting principles, advantages, and disadvantages are cognizable by the electronics engineer and technician and, indeed, by anybody involved in the design and manufacture of printed circuit boards. Provided the assembly is well executed, the junctions made by through hole assembly are strong and reliable, will resist adverse operating conditions, and endure.