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PTH Assembly - An Old Technology with New Uses

12th February 2014

What Is Pin-Through-Hole (PTH) Assembly?

PTH assembly is the oldest form of printed circuit board (PCB) assembly. A PCB is a simple board (usually made of laminate) that has conductive copper tracking etched on to its surface.

Electrical components such as resistors, diodes and capacitors can be easily assembled on the board and connected together via the copper tracks. The electrical components are then usually soldered on to the board on its reverse side.

Although surface mount assembly and Surface Mount Technology (SMT) are now the dominant technologies for PCBs, PTH is still widely used, especially in 'mixed' board solutions which combine SMT and PTH on the same PCB.

PTH assembly involves the drilling of many tiny holes into the PCB, into which the long-lead components are then fitted. With SMT, the components are mounted on the surface of the PCB so no drilling is required.

Long-lead devices are mounted into the drilled holes, trimmed and then soldered into place. This requires either a skilled technician to hand-solder each component or wave solder apparatus can be used to bulk-solder components.

PTH PCBs can be either single-sided or double-sided — in other words, they can have components on just one side or on both sides. After the long-lead devices have been inserted into the holes on the PCB, their leads are then bent back along the line of the copper tracking prior to soldering.

What Are The Advantages Of Sticking With PTH For Some Uses?

PTH assembly is less commonplace these days than it was ten years ago but it is still used, especially in SMT/PTH hybrid boards. In certain cases it is not economical for a company to have their existing PTH assemblies redesigned as SMT boards and so they continue to use their PTH solution. This is especially applicable to products which are approaching discontinuation.

PTH boards use components that are tried and tested and perform predictably and reliably. For these reasons, many manufacturers have been unwilling to convert to SMT components for fear that the new SMT solution will perform in a slightly different way to their original PTH board. There are also practical and economical reasons why some manufacturers prefer to stick with PTH boards.

If you have a requirement for PTH PCB assemblies or you are considering their use for a new solution and are interested in PCB prototyping, then please do not hesitate to contact us.