In electronics, through-hole technology (also spelled "thru-hole") is a manufacturing scheme in which leads on the components are inserted through 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]
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]
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.
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.
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.
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.
Wire wrap is an electronic component assembly technique that was invented to wire telephone crossbar switches, and later adapted to construct electronic circuit boards. Electronic components mounted on an insulating board are interconnected by lengths of insulated wire run between their terminals, with the connections made by wrapping several turns of uninsulated sections of the wire around a component lead or a socket pin.
A printed circuit board (PCB), also called printed wiring board (PWB), is a medium used to connect or "wire" components to one another in a circuit. It takes the form of a laminated sandwich structure of conductive and insulating layers: each of the conductive layers is designed with a pattern of traces, planes and other features etched from one or more sheet layers of copper laminated onto and/or between sheet layers of a non-conductive substrate. Electrical components may be fixed to conductive pads on the outer layers in the shape designed to accept the component's terminals, generally by means of soldering, to both electrically connect and mechanically fasten them to it. Another manufacturing process adds vias, plated-through holes that allow interconnections between layers.
In electronics, point-to-point construction is a non-automated technique for constructing circuits which was 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.
A breadboard, solderless breadboard, or protoboard is a construction base used to build semi-permanent prototypes of electronic circuits. Unlike a perfboard or stripboard, breadboards do not require soldering or destruction of tracks and are hence reusable. For this reason, breadboards are also popular with students and in technological education.
Surface-mount technology (SMT), originally called planar mounting, 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 is the generic name for a widely used type of electronics prototyping material for circuit boards characterized by a pre-formed 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 on an insulating bonded paper 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. It 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.
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).
In electronics, desoldering is the removal of solder and components from a circuit board for troubleshooting, repair, replacement, and salvage.
Wave soldering is a bulk soldering process used for the manufacturing 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 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 by soldering individual joints with a hot air pencil.
A via is an electrical connection between two or more metal layers, and are commonly used in printed circuit boards (PCB). Essentially a via is a small drilled hole that goes through two or more adjacent layers; the hole is plated with metal that forms an electrical connection through the insulating layers.
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 usually, but not always, 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 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-re-flow as well as other stages.
An electronic circuit is composed of individual electronic components, such as resistors, transistors, capacitors, inductors and diodes, connected by conductive wires or traces through which electric current can flow. It is a type of electrical circuit. For a circuit to be referred to as electronic, rather than electrical, generally at least one active component must be present. The combination of components and wires allows various simple and complex operations to be performed: signals can be amplified, computations can be performed, and data can be moved from one place to another.
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. 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. The name "Occam" comes from a quotation by William of Ockham.
In electronics, prototyping means building an actual circuit to a theoretical design to verify that it works, and to provide a physical platform for debugging it if it does not. The prototype is often constructed using techniques such as wire wrapping or using a breadboard, stripboard or perfboard, with the result being a circuit that is electrically identical to the design but not physically identical to the final product.
Hole sizes for through-hole parts at Wikibooks