Through-hole technology

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Through-hole (leaded) resistors Resistors (1).jpg
Through-hole (leaded) resistors

Through-hole technology (also spelled "thru-hole"), refers to the mounting scheme used for electronic components that involves the use of leads on the components that are inserted into holes drilled in printed circuit boards (PCB) and soldered to pads on the opposite side either by manual assembly (hand placement) or by the use of automated insertion mount machines. [1] [2]

Contents

History

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 MOS6581 chtaube061229.jpg
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
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 1mm diameter. Plated-through holes on an electronic circuit board.jpg
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 1mm diameter.

Through-hole technology almost completely replaced earlier electronics assembly techniques such as point-to-point construction. From the 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 vias. [2]

Leads

Axial and radial leads

Axial- (top) and radial- (bottom) leaded electrolytic capacitors Capacitors electrolytic.jpg
Axial- (top) and radial- (bottom) leaded electrolytic capacitors

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. [3] [4] [5]

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 disk capacitor). [5] 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, [3] [4] 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. [4] Extra insulation with heat-shrink tubing may be used to prevent 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 automated component placement machinery, and poorer reliability because of reduced vibration and mechanical shock resistance in the completed assembly.

Multiple lead devices

Components like integrated circuits can have upwards of dozens of leads, or pins Integrated Circuit.jpg
Components like integrated circuits 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 packages are used, either directly onto the PCB or via a socket.

Characteristics

A box of drill bits 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. Box of 02in pcb bits.jpg
A box of drill bits 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 traces 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 capacitors or semiconductors in larger packages such as the TO-220 that require the additional mounting strength, or for components such as plug connectors or electromechanical relays that require great strength in support. [4]

Design engineers often prefer the larger through-hole rather than surface mount parts when prototyping, because they can be easily used with breadboard sockets. 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 prototyping circuits with breadboards using microprocessors such as Arduino or PICAXE. These components are large enough to be easy to use and solder by hand.

See also

Related Research Articles

Dual in-line package Type of electronic component package

In microelectronics, a dual in-line package, is an electronic component package with a rectangular housing and two parallel rows of electrical connecting pins. The package may be through-hole mounted to a printed circuit board (PCB) or inserted in a socket. The dual-inline format was invented by Don Forbes, Rex Rice and Bryant Rogers at Fairchild R&D in 1964, when the restricted number of leads available on circular transistor-style packages became a limitation in the use of integrated circuits. Increasingly complex circuits required more signal and power supply leads ; eventually microprocessors and similar complex devices required more leads than could be put on a DIP package, leading to development of higher-density chip carriers. Furthermore, square and rectangular packages made it easier to route printed-circuit traces beneath the packages.

Printed circuit board Board to support and connect electronic components

A printed circuit board (PCB) is a laminated sandwich structure of conductive and insulating layers. PCBs have two complementary functions. The first is to affix electronic components in designated locations on the outer layers by means of soldering. The second is to provide reliable electrical connections between the component's terminals in a controlled manner often referred to as PCB design. Each of the conductive layers is designed with an artwork pattern of conductors that provides electrical connections on that conductive layer. Another manufacturing process adds vias, plated-through holes that allow interconnections between layers.

Point-to-point construction

Point-to-point construction is a non-automated method of construction of electronics circuits widely used before the use of printed circuit boards (PCBs) and automated assembly gradually became widespread following their introduction in the 1950s. Circuits using thermionic valves were relatively large, relatively simple, and used large sockets, all of which made the PCB less obviously advantageous than with later complex semiconductor circuits. Point-to-point construction is still widespread in power electronics where components are bulky and serviceability is a consideration, and to construct prototype equipment with few or heavy electronic components. A common practice, especially in older point-to-point construction, is to use the leads of components such as resistors and capacitors to bridge as much of the distance between connections as possible, reducing the need to add additional wire between the components.

Breadboard Board with embedded spring clips that allows for electronics to be wired without soldering

A breadboard, or protoboard, is a construction base for prototyping of electronics. Originally the word referred to a literal bread board, a polished piece of wood used when slicing bread. In the 1970s the solderless breadboard became available and nowadays the term "breadboard" is commonly used to refer to these.

Surface-mount technology Method for producing electronic circuits

Surface-mount technology (SMT) is a method in which the electrical components are mounted directly onto the surface of a printed circuit board (PCB). An electrical component mounted in this manner is referred to as a surface-mount device (SMD). In industry, this approach has largely replaced the through-hole technology construction method of fitting components, in large part because SMT allows for increased manufacturing automation which reduces cost and improves quality. It also allows for more components to fit on a given area of substrate. Both technologies can be used on the same board, with the through-hole technology often used for components not suitable for surface mounting such as large transformers and heat-sinked power semiconductors.

Stripboard

Stripboard is the generic name for a widely used type of electronics prototyping board characterized by a 0.1 inches (2.54 mm) regular (rectangular) grid of holes, with wide parallel strips of copper cladding running in one direction all the way across one side of the board. It is commonly also known by the name of the original product Veroboard, which is a trademark, in the UK, of British company Vero Technologies Ltd and Canadian company Pixel Print Ltd. In using the board, breaks are made in the tracks, usually around holes, to divide the strips into multiple electrical nodes. With care, it is possible to break between holes to allow for components that have two pin rows only one position apart such as twin row headers for IDCs.

Quad flat package Surface mount integrated circuit package with "gull wing" pins extinding from all sides

A quad flat package (QFP) is a surface-mounted integrated circuit package with "gull wing" leads extending from each of the four sides. Socketing such packages is rare and through-hole mounting is not possible. Versions ranging from 32 to 304 pins with a pitch ranging from 0.4 to 1.0 mm are common. Other special variants include low-profile QFP (LQFP) and thin QFP (TQFP).

Desoldering

In electronics, desoldering is the removal of solder and components from a circuit board for troubleshooting, repair, replacement, and salvage.

Wave soldering

Wave soldering is a bulk soldering process used in the manufacture of printed circuit boards. The circuit board is passed over a pan of molten solder in which a pump produces an upwelling of solder that looks like a standing wave. As the circuit board makes contact with this wave, the components become soldered to the board. Wave soldering is used for both through-hole printed circuit assemblies, and surface mount. In the latter case, the components are glued onto the surface of a printed circuit board (PCB) by placement equipment, before being run through the molten solder wave. Wave soldering is mainly used in soldering of through hole components.

Reflow soldering

Reflow soldering is a process in which a solder paste is used to temporarily attach one or thousands of tiny electrical components to their contact pads, after which the entire assembly is subjected to controlled heat. The solder paste reflows in a molten state, creating permanent solder joints. Heating may be accomplished by passing the assembly through a reflow oven, under an infrared lamp, or (unconventionally) by soldering individual joints with a desoldering hot air pencil.

Hybrid integrated circuit Miniature electronic circuit combining different semiconductor devices and passive components on a substrate

A hybrid integrated circuit (HIC), hybrid microcircuit, hybrid circuit or simply hybrid is a miniaturized electronic circuit constructed of individual devices, such as semiconductor devices and passive components, bonded to a substrate or printed circuit board (PCB). A PCB having components on a Printed Wiring Board (PWB) is not considered a true hybrid circuit according to the definition of MIL-PRF-38534.

A via is an electrical connection between copper layers in a printed circuit board. Essentially a via is a small drilled hole that goes through two or more adjacent layers; the hole is plated with copper that forms electrical connection through the insulation that separates the copper layers.

An electronic kit is a package of electrical components used to build an electronic device. Generally, kits are composed of electronic components, a circuit diagram (schematic), assembly instructions and often a printed circuit board (PCB) or another type of prototyping board.

Flat no-leads package Integrated circuit package with contacts on all 4 sides, on the underside of the package

Flat no-leads packages such as quad-flat no-leads (QFN) and dual-flat no-leads (DFN) physically and electrically connect integrated circuits to printed circuit boards. Flat no-leads, also known as micro leadframe (MLF) and SON, is a surface-mount technology, one of several package technologies that connect ICs to the surfaces of PCBs without through-holes. Flat no-lead is a near chip scale plastic encapsulated package made with a planar copper lead frame substrate. Perimeter lands on the package bottom provide electrical connections to the PCB. Flat no-lead packages include an exposed thermally conductive pad to improve heat transfer out of the IC. Heat transfer can be further facilitated by metal vias in the thermal pad. The QFN package is similar to the quad-flat package (QFP), and a ball grid array (BGA).

Perfboard

Perfboard is a material for prototyping electronic circuits. It is a thin, rigid sheet with holes pre-drilled at standard intervals across a grid, usually a square grid of 0.1 inches (2.54 mm) spacing. These holes are ringed by round or square copper pads, though bare boards are also available. Inexpensive perfboard may have pads on only one side of the board, while better quality perfboard can have pads on both sides. Since each pad is electrically isolated, the builder makes all connections with either wire wrap or miniature point to point wiring techniques. Discrete components are soldered to the prototype board such as resistors, capacitors, and integrated circuits. The substrate is typically made of paper laminated with phenolic resin or a fiberglass-reinforced epoxy laminate (FR-4).

Automated optical inspection (AOI) is an automated visual inspection of printed circuit board (PCB) manufacture where a camera autonomously scans the device under test for both catastrophic failure and quality defects. It is commonly used in the manufacturing process because it is a non-contact test method. It is implemented at many stages through the manufacturing process including bare board inspection, solder paste inspection (SPI), pre-reflow and post-reflow as well as other stages.

Thick-film technology

Thick-film technology is used to produce electronic devices/modules such as surface mount devices modules, hybrid integrated circuits, heating elements, integrated passive devices and sensors. Main manufacturing technique is screen printing (stenciling), which in addition to use in manufacturing electronic devices can also be used for various graphic reproduction targets. The technique is known in its basic form about thousand years – already used during great Chinese dynasties. It became one of the key manufacturing/miniaturisation techniques of electronic devices/modules during 1950s. Typical film thickness – manufactured with thick film manufacturing processes for electronic devices – is 0.0001 to 0.1 mm.

The Occam process is a solder-free, Restriction of Hazardous Substances Directive (RoHS)-compliant method for use in the manufacturing of electronic circuit boards developed by Verdant Electronics. It combines the usual two steps of the construction of printed circuit boards (PCBs) followed by the population process of placing various leaded and non-leaded electronic components into one process.

Veroboard

Veroboard is a brand of stripboard, a pre-formed circuit board material of copper strips on an insulating bonded paper board which was originated and developed in the early 1960s by the Electronics Department of Vero Precision Engineering Ltd (VPE). It was introduced as a general-purpose material for use in constructing electronic circuits - differing from purpose-designed printed circuit boards (PCBs) in that a variety of electronics circuits may be constructed using a standard wiring board.

References

  1. Electronic Packaging:Solder Mounting Technologies in K.H. Buschow et al (ed), Encyclopedia of Materials:Science and Technology, Elsevier, 2001 ISBN   0-08-043152-6, pages 2708-2709
  2. 1 2 Horowitz, Paul; Hill, Winfield (1989). The art of electronics (PDF) (2nd ed.). Cambridge [u.a.]: Cambridge Univ. Press. ISBN   9780521370950.
  3. 1 2 "All About Capacitors". Beavis Audio Research. Retrieved 2013-05-16.
  4. 1 2 3 4 "What Is an Axial Lead?". wiseGEEK: clear answers for common. Conjecture Corporation. Retrieved 2013-05-16.
  5. 1 2 Bilotta, Anthony J. (1985). Connections in electronic assemblies. New York: M. Dekker. p. 205. ISBN   9780824773199.