View source for Through-hole technology

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[[File:Resistors (1).jpg|thumb|right|Through-hole (leaded) resistors]]
[[File:MOS6581 chtaube061229.jpg|thumb|right|Through-hole devices mounted on the circuit board of a mid-1980's [[home computer]].]]
'''Through-hole technology''', also spelled "thru-hole", refers to the mounting scheme used for electronic components that involves the use of [[Lead (electronics)|lead]]s on the components that are inserted into holes (PTH - Plated Through-Hole) drilled in [[printed circuit board]]s (PCB) and [[soldering|soldered]] to pads on the opposite side either by manual assembly by hand placement or by the use of automated insertion mount machines. <ref name= MAT2001> ''Electronic Packaging:Solder Mounting Technlogies'' in K.H. Buschow et al (ed), ''Encyclopedia of Materials:Science and Technolgy'', Elsevier, 2001 ISBN 0-08-043152-6,  pages 2708-2709 </ref>

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 became popular in the late 1980s, every component on a typical PCB was a through-hole component.

While through-hole mounting provides strong mechanical bonds when compared to [[surface-mount technology]] 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 components such as [[electrolytic capacitor]]s or [[semiconductor]]s in larger packages such as the [[TO220]] that require the additional mounting strength, or for components such as plug connectors or electromechanical relays that require great strength in support.

Design engineers often prefer the larger through-hole to surface mount parts when prototyping because they can be used with [[breadboard]]s, making them easier to handle, insert, and solder.

A [[rule of thumb]] for creating a through-hole on a PCB is to make the drill diameter 0.019” (0.48mm) larger than the part’s lead.{{Citation needed|date=April 2010}}  Horizontal installation of axial-leaded through-hole parts (e.g. resistor, capacitors, and diodes) is done by bending the leads 90 degrees in the same direction, inserting part in the board, bending leads located on the back of the board in opposing directions to improve the part's mechanical strength; finally, soldering the leads such that the solder seeps through to both sides of the board. Later the assembler cuts off the excess leads.

Installation of radial-leaded parts (e.g. [[LED]]s and [[electrolytic capacitor]]s) and [[IC]]s are done in the same manner except the parts are already formed in a 90° direction.
[[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.]]
== See also ==
{{wikibooks
 |1= Practical Electronics
 |2= PCB Layout#Holes
 |3= hole sizes for through-hole parts
}}
* [[Via (electronics)]]
* [[Board to board connectors]] 
* [[Surface-mount technology]]

==References==
<references/>

[[Category:Electronic design]]
[[Category:Electronics manufacturing]]
[[Category:Chip carriers]]


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