Editing Through-hole technology

{{Short description|Circuit board manufacturing technique}}
{{Use dmy dates|date=August 2022|cs1-dates=y}}
{{Use list-defined references|date=August 2022}}
[[File:Resistors (1).jpg|thumb|right|Through-hole (leaded) resistors]]

In [[electronics]], '''through-hole technology''' (also spelled "'''thru-hole'''") is a manufacturing scheme in which [[lead (electronics)|lead]]s on the [[electronic component|components]] are inserted [[through hole]]s drilled in [[printed circuit board]]s (PCB) and [[soldering|soldered]] to pads on the opposite side, either by manual assembly (hand placement) or by the use of automated [[Insertion mount machine|insertion mount machines]].<ref name="Buschow_2001"/><ref name="Horowitz-Hill_1989"/>

==History==
[[File:MOS6581 chtaube061229.jpg|thumb|right|Through-hole devices mounted on the circuit board of a mid-1980s [[home computer]]. Axial-lead devices are at upper left, while blue radial-lead capacitors are at upper right]]
[[File:Plated-through_holes_on_an_electronic_circuit_board.jpg|thumb|right|Close-up view of an electronic circuit board showing component lead holes (gold-plated) with through-hole plating up the sides of the hole to connect tracks on both sides of the board. The holes are circa 1&nbsp;mm diameter.]]
Through-hole technology almost completely replaced earlier electronics assembly techniques such as [[point-to-point construction]]. From the [[history of computing hardware|second generation of computers]] in the 1950s until [[surface-mount technology]] (SMT) became popular in the mid 1980s, every component on a typical PCB was a through-hole component. PCBs initially had tracks printed on one side only, later both sides, then multi-layer boards were in use. Through holes became '''plated-through holes''' (PTH) in order for the components to make contact with the required conductive layers. Plated-through holes are no longer required with SMT boards for making the component connections, but are still used for making interconnections between the layers and in this role are more usually called [[via (electronics)|vias]].<ref name="Horowitz-Hill_1989"/>

==Leads==
==={{Anchor|NPTH|PTH|Axial vs. radial leads}}Axial and radial leads===
[[File:Capacitors electrolytic.jpg|thumb|right|Axial- (top) and radial- (bottom) leaded [[electrolytic capacitor]]s]]
Components with wire leads are generally used on through-hole boards. Axial leads protrude from each end of a typically [[cylindrical]] or elongated box-shaped component, on the geometrical [[axis of symmetry]]. Axial-leaded components resemble wire jumpers in shape, and can be used to span short distances on a board, or even otherwise unsupported through an open space in [[point-to-point wiring]]. Axial components do not protrude much above the surface of a board, producing a low-profile or flat configuration when placed "lying down" or parallel to the board.<ref name="BAR"/><ref name="WG"/><ref name="Bilotta_1985"/>

Radial leads project more or less in parallel from the same surface or aspect of a component package, rather than from opposite ends of the package. Originally, radial leads were defined as more-or-less following a [[radius]] of a cylindrical component (such as a [[ceramic capacitor|ceramic disk capacitor]]).<ref name="Bilotta_1985"/> Over time, this definition was generalized in contrast to axial leads, and took on its current form. When placed on a board, radial components "stand up" perpendicular,<ref name="BAR"/><ref name="WG"/> occupying a smaller footprint on sometimes-scarce "board real estate", making them useful in many high-density designs. The parallel leads projecting from a single mounting surface gives radial components an overall "plugin nature", facilitating their use in high-speed automated component insertion ("board-stuffing") machines.

When needed, an axial component can be effectively converted into a radial component, by bending one of its leads into a "U" shape so that it ends up close to and parallel with the other lead.<ref name="WG"/> Extra insulation with [[heat-shrink tubing]] may be used to prevent [[short circuit|shorting out]] on nearby components. Conversely, a radial component can be pressed into service as an axial component by separating its leads as far as possible, and extending them into an overall length-spanning shape. These improvisations are often seen in [[breadboard]] or [[prototype]] construction, but are [[deprecated]] for [[mass production]] designs. This is because of difficulties in use with [[SMT placement equipment|automated component placement machinery]], and poorer [[reliability engineering|reliability]] because of reduced [[vibration]] and [[mechanical shock]] resistance in the completed assembly.
<!-- Installation of radial-leaded parts (e.g. [[LED]]s and [[electrolytic capacitor]]s) and [[integrated circuit]]s is done in the same manner except the parts are already formed in a 90° direction. -->

===Multiple lead devices===
[[File:Integrated Circuit.jpg|thumb|Components like [[integrated circuit]]s can have upwards of dozens of leads, or ''pins'']]
For electronic components with two or more leads, for example, diodes, transistors, ICs, or resistor packs, a range of standard-sized [[semiconductor package]]s are used, either directly onto the PCB or via a socket.

==Characteristics==
[[File:Box of 02in pcb bits.jpg|thumb|right|A box of [[drill bit]]s used for making holes in printed circuit boards. While tungsten-carbide bits are very hard, they eventually wear out or break. Making holes is a considerable part of the cost of a through-hole printed circuit board.]]

While through-hole mounting provides strong mechanical bonds when compared to SMT techniques, the additional drilling required makes the boards more expensive to produce. They also limit the available routing area for [[signal trace]]s on layers immediately below the top layer on multilayer boards since the holes must pass through all layers to the opposite side. To that end, through-hole mounting techniques are now usually reserved for bulkier or heavier components such as [[electrolytic capacitor]]s or [[semiconductor]]s in larger packages such as the [[TO-220]] that require the additional mounting strength, or for components such as [[electrical connector|plug connector]]s or [[electromechanical relay]]s that require great strength in support.<ref name="WG"/>

Design engineers often prefer the larger through-hole rather than surface mount parts when prototyping, because they can be easily used with [[breadboard|breadboard socket]]s. However, high-speed or high-frequency designs may require SMT technology to minimize stray [[inductance]] and [[capacitance]] in wire leads, which would impair circuit function. Ultra-compact designs may also dictate SMT construction, even in the prototype phase of design.

Through-hole components are ideal for [[Prototype|prototyping]] circuits with [[Breadboard|breadboards]] using microprocessors such as [[Arduino]] or [[PICAXE]]. These components are large enough to be easy to use and solder by hand.

==See also==
* [[Point-to-point construction]]
* [[Board-to-board connector]]
* [[Surface-mount technology]]
* [[Via (electronics)]]

==References==
{{reflist|refs=
<ref name="Buschow_2001">''Electronic Packaging: Solder Mounting Technologies'' in K. H. Buschow et al (eds.), ''Encyclopedia of Materials: Science and Technology'', [[Elsevier]], 2001 {{ISBN|0-08-043152-6}}, pp. 2708–2709</ref>
<ref name="Horowitz-Hill_1989">{{cite book |title=The art of electronics |date=1989 |publisher=[[Cambridge University Press]] |location=Cambridge |isbn=978-0-52137095-0 |edition=2nd |author-last1=Horowitz |author-first1=Paul |author-last2=Hill |author-first2=Winfield |url-access=registration |url=https://artofelectronics.net/wp-content/uploads/2016/02/AoE3_chapter9.pdf}}</ref>
<ref name="BAR">{{cite web |title=All About Capacitors |url=http://www.beavisaudio.com/techpages/Caps/ |work=Beavis Audio Research |access-date=2013-05-16}}</ref>
<ref name="WG">{{cite web |title=What Is an Axial Lead? |url=http://www.wisegeek.com/what-is-an-axial-lead.htm |work=wiseGEEK: clear answers for common |publisher=Conjecture Corporation |access-date=2013-05-16}}</ref>
<ref name="Bilotta_1985">{{cite book |author-last=Bilotta |author-first=Anthony J. |title=Connections in electronic assemblies |date=1985 |publisher=M. Dekker |location=New York |isbn=978-0-82477319-9 |page=205}}</ref>
}}

==Further reading==
* {{cite web |url=http://mobiledevdesign.com/hardware_news/radio_new_face_aviation_2/ |title=The Future of Commercial Aviation |publisher=Mobile Development and Design Magazine |date=2002-01-01 |access-date=2011-12-30 |author-last1=Lesser |author-first1=Roger |author-last2=Alderton |author-first2=Megan}}
* {{cite web |url=http://goliath.ecnext.com/coms2/gi_0199-2680304/Flexible-production-cell-for-led.html |title=Flexible production cell for led arrays. (Spotlight: electronic displays) |publisher=Canadian Electronics |date=2003-03-01 |access-date=2011-12-30 |url-access=subscription}}
* {{cite web |url=http://pcdandf.com/cms/magazine/171-current-issue/6990-component-layout-in-placement-processes |title=Component Layout in Placement Processes |publisher=Printed Circuit Design & Fab |date=2010-02-01 |access-date=2011-12-30 |author-last=Khan |author-first=Zulki}}
* {{cite web |url=http://www.pcworld.fr/article/kingston-memoire-vive-dram-hyper-x-datatraveler/la-fabrication/478881/ |title=Fabrication: Visiting a production line of Kingston memory modules |magazine=PC World (France) |issn= |date=2010-03-10 |access-date=2011-12-30 |author-last=Charpentier |author-first=Stephane |language=fr |url-status=dead |archive-url=https://web.archive.org/web/20120426082300/http://www.pcworld.fr/article/kingston-memoire-vive-dram-hyper-x-datatraveler/la-fabrication/478881/ |archive-date=2012-04-26}}

==External links==
* {{Wikibooks-inline|Practical Electronics|PCB Layout#Holes|Hole sizes for through-hole parts}}

[[Category:Chip carriers]]
[[Category:Printed circuit board manufacturing]]