Through Hole Technology

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As Through Hole ( English through-hole technology , THT; pin-in-hole technology , PIH) is referred to in the assembly and interconnection technology a mounting manner of wired electronic components . In contrast to surface mounting ( surface-mounting technology , SMT), through-hole mounting is characterized in that the components have wire connections (“wired components”). During assembly, these are inserted through contact holes in the circuit board and then connected to the conductor track by soldering (conventional hand soldering , wave soldering or selective soldering ).

Wired resistor on a printed circuit board in through hole mounting

technology

Wired resistors before being fitted with a conveyor belt

From the end of the 1960s, the electrical components of an electrical circuit, previously mostly individually soldered to solder posts , were assembled and soldered together on a printed circuit board provided with holes and conductor tracks . Standardization has established the center-to-center spacing of the holes from one another to be 2.54 mm or a multiple thereof on the basis of inches . This laid the foundation for the automatic assembly of wired components. Although the automatic placement machines available at the time were able to fit both capacitors and resistors in an axially lying and radially upright (connections led out on one side) design, the radial design with radial connections in the standardized grid dimension prevailed for the passive components because, due to the smaller circuit board Surface was cheaper. Wired components such as resistors for industrial assembly are delivered on belts without a grid dimension. Before assembly, the connections are cut to the appropriate length and bent in the grid and then assembled on the circuit board. For semiconductor components that have multiple connections, both the single-in-line housing and the dual-in-line housing with a pitch of 2.54 mm are used for conventional circuit board assembly .

The assembly technology with wired components has declined sharply with the introduction of the SMD assembly technology, which leads to a significantly higher component density and minimization of the holes in the circuit board and thus overall reduces manufacturing costs. However, it is often not possible to completely do without bores in the circuit board, as these are required in the form of plated-through holes for electrical connection across several layers. There are also larger components such as transformers that are only available with connecting wires and not in an SMD design.

Areas of application

Wired components on a THT circuit board
THT-equipped circuit board, top side

Information electronics

In the field of information electronics, wired components have largely been replaced by SMD components in the industrial sector. Simple and inexpensive products in the consumer sector will continue to be produced partially or completely with wired components.

Power electronics

In the field of power electronics, standard wired components are still used because of the required current-carrying capacity of the components themselves and the connection of the current-carrying components to the various layers of the circuit board.

Some components with a high mechanical load (e.g. connectors , larger switches , larger electrolytic capacitors , power coils and power semiconductors ) still have to be attached to the circuit board by means of through-hole mounting, because there are often no SMD designs for these components. For purely surface-mounted components, if there is a high mechanical load or a high current load, there is a risk that the soldering point or the conductor track will be stressed or damaged too much. For this reason, printed circuit boards are often mixed with components. This has the disadvantage that the THT process cannot be fully automated and thus causes additional costs.

Handcrafted devices

Devices that are hand-soldered by craftsmen or amateur electronics enthusiasts are usually manufactured with wired components because they are easier to use. So they keep z. B. even during the soldering process in the circuit board, while SMD components have to be fixed. Due to their size, wired components are less prone to overheating and can also be soldered with conventional soldering irons. Due to their size, their types can also be easily recognized with the naked eye, and they can be easily processed with bare hands.

Electrical device kits are typically designed with wired components. Since the soldering process is carried out by the end user, the work of the industry is limited to etching the circuit board and packaging the components. So there are hardly any additional costs for the industry, but a larger group of customers is tapped.

Occasionally, however, SMD components are also used in these areas if small size or good high-frequency properties are important.

THT reflow technology

In the age of SMD assembly using automatic assembly machines and automated soldering processes, it was therefore advisable to use the reflow soldering process , for example, connectors that are actually not suitable for this type of construction . In this context, through-hole-reflow technology (THR) was developed. Through-hole components are designed for automatic assembly and the high thermal load in the reflow oven. In this way, the assembly costs for automatic circuit board assembly can be reduced, since some process steps of normal THT assembly are omitted.

The terms PiP - "Pin in Paste" and PIHIR - "Pin in Hole Intrusive Reflow" are also used for THR technology .

Individual evidence

  1. a b Wolfgang Scheel (ed.): Assembly technology of electronics. Assembly. 2nd, updated and expanded edition. Verlag Technik, Berlin 1999, ISBN 3-341-01234-6 , p. 11.