![Smt closeup](https://upload.wikimedia.org/wikipedia/commons/6/6b/Smt_closeup.jpg)
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
A printed circuit board (PCB; also printed wiring board or PWB) is a medium used in Electrical engineering, electrical and electronic engineering to connect electronic components to one another in a controlled manner. It takes the form of a L ...
(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
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 ...
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.
An SMT component is usually smaller than its through-hole counterpart because it has either smaller leads or no leads at all. It may have short
pin
A pin is a device used for fastening objects or material together.
Pin or PIN may also refer to:
Computers and technology
* Personal identification number (PIN), to access a secured system
** PIN pad, a PIN entry device
* PIN, a former Dutch ...
s or leads of various styles, flat contacts, a matrix of
solder ball
In integrated circuit packaging, a solder ball, also a solder bump (ofter referred to simply as "ball" or "bumps") is a ball of solder that provides the contact between the chip package and the printed circuit board, as well as between stacked pa ...
s (
BGAs), or terminations on the body of the component.
History
Surface-mount technology was developed in the 1960s. By 1986 surface mounted components accounted for 10% of the market at most, but was rapidly gaining popularity. By the late 1990s, the great majority of high-tech electronic printed circuit assemblies were dominated by surface mount devices. Much of the pioneering work in this technology was done by
IBM. The design approach first demonstrated by IBM in 1960 in a small-scale computer was later applied in the
Launch Vehicle Digital Computer
The Launch Vehicle Digital Computer (LVDC) was a computer that provided the autopilot for the Saturn V rocket from launch to Earth orbit insertion. Designed and manufactured by IBM's Electronics Systems Center in Owego, New York, it was one of th ...
used in the
Instrument Unit that guided all
Saturn IB and
Saturn V
Saturn V is a retired American super heavy-lift launch vehicle developed by NASA under the Apollo program for human exploration of the Moon. The rocket was human-rated, with multistage rocket, three stages, and powered with liquid-propellant r ...
vehicles.
Components were mechanically redesigned to have small metal tabs or end caps that could be directly soldered to the surface of the PCB. Components became much smaller and component placement on both sides of a board became far more common with surface mounting than through-hole mounting, allowing much higher circuit densities and smaller circuit boards and, in turn, machines or subassemblies containing the boards.
Often the surface tension of the solder is enough to hold the parts to the board; in rare cases parts on the bottom or "second" side of the board may be secured with a dot of adhesive to keep components from dropping off inside
reflow oven
A reflow oven is a machine used primarily for reflow soldering of surface mount electronic components to printed circuit boards (PCBs).
In commercial high-volume use, reflow ovens take the form of a long tunnel containing a conveyor belt along wh ...
s if the part is above the limit of 30g per square inch of pad area. Adhesive is sometimes used to hold SMT components on the bottom side of a board if a
wave soldering
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 ci ...
process is used to solder both SMT and through-hole components simultaneously. Alternatively, SMT and through-hole components can be soldered on the same side of a board without adhesive if the SMT parts are first reflow-soldered, then a
selective solder mask is used to prevent the solder holding those parts in place from reflowing and the parts floating away during wave soldering. Surface mounting lends itself well to a high degree of automation, reducing labor cost and greatly increasing production rates.
Conversely, SMT does not lend itself well to manual or low-automation fabrication, which is more economical and faster for one-off prototyping and small-scale production, and this is one reason why many through-hole components are still manufactured. Some SMDs can be soldered with a temperature-controlled manual soldering iron, but unfortunately, those that are very small or have too fine a lead pitch are impossible to manually solder without expensive hot-air solder reflow equipment. SMDs can be one-quarter to one-tenth the size and weight, and one-half to one-quarter the cost of equivalent through-hole parts, but on the other hand, the costs of a certain SMT part and of an equivalent through-hole part may be quite similar, though rarely is the SMT part more expensive.
Common abbreviations
Different terms describe the components, technique, and machines used in manufacturing. These terms are listed in the following table:
Assembly techniques
![SMT-Bestueckung](https://upload.wikimedia.org/wikipedia/commons/a/a9/SMT-Bestueckung.jpg)
Where components are to be placed, the
printed circuit board
A printed circuit board (PCB; also printed wiring board or PWB) is a medium used in Electrical engineering, electrical and electronic engineering to connect electronic components to one another in a controlled manner. It takes the form of a L ...
normally has flat, usually
tin
Tin is a chemical element with the symbol Sn (from la, stannum) and atomic number 50. Tin is a silvery-coloured metal.
Tin is soft enough to be cut with little force and a bar of tin can be bent by hand with little effort. When bent, t ...
-lead, silver, or gold plated
copper
Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkis ...
pads without holes, called ''solder pads''.
Solder paste
Solder paste is used in the manufacture of printed circuit boards to connect surface mount components to pads on the board. It is also possible to solder through-hole pin in paste components by printing solder paste in and over the holes. The s ...
, a sticky mixture of
flux and tiny solder particles, is first applied to all the solder pads with a stainless steel or nickel stencil using a
screen printing process. It can also be applied by a jet-printing mechanism, similar to an
inkjet printer
Inkjet printing is a type of computer printing that recreates a digital image by propelling droplets of ink onto paper and plastic substrates. Inkjet printers were the most commonly used type of printer in 2008, and range from small inexpensi ...
. After pasting, the boards proceed to the
pick-and-place machines, where they are placed on a conveyor belt. The components to be placed on the boards are usually delivered to the production line in either paper/plastic tapes wound on reels or plastic tubes. Some large integrated circuits are delivered in static-free trays.
Numerical control pick-and-place machines remove the parts from the tapes, tubes or trays and place them on the PCB.
The boards are then conveyed into the
reflow soldering
Reflow soldering is a process in which a solder paste (a sticky mixture of powdered solder and flux) is used to temporarily attach one or thousands of tiny electrical components to their contact pads, after which the entire assembly is subjec ...
oven. They first enter a pre-heat zone, where the temperature of the board and all the components is gradually, uniformly raised to prevent thermal shock. The boards then enter a zone where the temperature is high enough to melt the solder particles in the solder paste, bonding the component leads to the pads on the circuit board. The surface tension of the molten solder helps keep the components in place, and if the solder pad geometries are correctly designed,
surface tension automatically aligns the components on their pads.
There are a number of ''techniques'' for reflowing solder. One is to use
infrared
Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around ...
lamps; this is called infrared reflow. Another is to use a hot gas
convection
Convection is single or multiphase fluid flow that occurs spontaneously due to the combined effects of material property heterogeneity and body forces on a fluid, most commonly density and gravity (see buoyancy). When the cause of the convec ...
. Another technology which is becoming popular again is special
fluorocarbon liquids with high boiling points which use a method called vapor phase reflow. Due to environmental concerns, this method was falling out of favor until lead-free legislation was introduced which requires tighter controls on soldering. At the end of 2008, convection soldering was the most popular reflow technology using either standard air or nitrogen gas. Each method has its advantages and disadvantages. With infrared reflow, the board designer must lay the board out so that short components don't fall into the shadows of tall components. Component location is less restricted if the designer knows that vapor phase reflow or convection soldering will be used in production. Following reflow soldering, certain irregular or heat-sensitive components may be installed and soldered by hand, or in large-scale automation, by focused infrared beam (FIB) or localized convection equipment.
If the circuit board is double-sided then this printing, placement, reflow process may be repeated using either solder paste or glue to hold the components in place. If a
wave soldering
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 ci ...
process is used, then the parts must be
glued to the board prior to processing to prevent them from floating off when the solder paste holding them in place is melted.
After soldering, the boards may be washed to remove flux residues and any stray solder balls that could short out closely spaced component leads.
Rosin
Rosin (), also called colophony or Greek pitch ( la, links=no, pix graeca), is a solid form of resin obtained from pines and some other plants, mostly conifers, produced by heating fresh liquid resin to vaporize the volatile liquid terpene comp ...
flux is removed with fluorocarbon solvents, high
flash point
The flash point of a material is the "lowest liquid temperature at which, under certain standardized conditions, a liquid gives off vapours in a quantity such as to be capable of forming an ignitable vapour/air mixture". (EN 60079-10-1)
The fl ...
hydrocarbon
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic, and their odors are usually weak or ...
solvents, or low flash solvents e.g.
limonene
Limonene is a colorless liquid aliphatic hydrocarbon classified as a cyclic monoterpene, and is the major component in the oil of citrus fruit peels. The -isomer, occurring more commonly in nature as the fragrance of oranges, is a flavoring a ...
(derived from orange peels) which require extra rinsing or drying cycles. Water-soluble fluxes are removed with
deionized water
Purified water is water that has been mechanically filtered or processed to remove impurities and make it suitable for use. Distilled water was, formerly, the most common form of purified water, but, in recent years, water is more frequently puri ...
and detergent, followed by an air blast to quickly remove residual water. However, most electronic assemblies are made using a "No-Clean" process where the flux residues are designed to be left on the circuit board, since they are considered harmless. This saves the cost of cleaning, speeds up the manufacturing process, and reduces waste. However, it is generally suggested to wash the assembly, even when a "No-Clean" process is used, when the application uses very high frequency clock signals (in excess of 1 GHz). Another reason to remove no-clean residues is to improve adhesion of
conformal coating
Conformal coating is a protective coating of thin polymeric film, applied to printed circuit boards (PCB). The coating is named conformal since it ''conforms'' to the contours of the PCB. Conformal coatings are typically applied at 25-250 μm to ...
s and underfill materials. Regardless of cleaning or not those PCBs, current industry trend suggests to carefully review a PCB assembly process where "No-Clean" is applied, since flux residues trapped under components and RF shields may affect surface insulation resistance (SIR), especially on high component density boards.
Certain manufacturing standards, such as those written by the
IPC - Association Connecting Electronics Industries require cleaning regardless of the solder flux type used to ensure a thoroughly clean board. Proper cleaning removes all traces of solder flux, as well as dirt and other contaminants that may be invisible to the naked eye. No-Clean or other soldering processes may leave "white residues" that, according to IPC, are acceptable "provided that these residues have been qualified and documented as benign". However, while shops conforming to IPC standard are expected to adhere to the Association's rules on board condition, not all manufacturing facilities apply IPC standard, nor are they required to do so. Additionally, in some applications, such as low-end electronics, such stringent manufacturing methods are excessive both in expense and time required.
Finally, the boards are visually inspected for missing or misaligned components and solder bridging. If needed, they are sent to a
rework station where a human operator repairs any errors. They are then usually sent to the testing stations (
in-circuit test
In-circuit testing (ICT) is an example of white box testing where an electrical probe tests a populated printed circuit board (PCB), checking for shorts, opens, resistance, capacitance, and other basic quantities which will show whether the assemb ...
ing and/or functional testing) to verify that they operate correctly.
Automated optical inspection (AOI) systems are commonly used in PCB manufacturing. This technology has proven highly efficient for process improvements and quality achievements.
Advantages
![RC2010JK-071K2L](https://upload.wikimedia.org/wikipedia/commons/e/ec/RC2010JK-071K2L.jpg)
The main advantages of SMT over the older through-hole technique are:
* Smaller components.
* Much higher component density (components per unit area) and many more connections per component.
* Components can be placed on both sides of the circuit board.
* Higher density of connections because holes do not block routing space on inner layers, nor on back-side layers if components are mounted on only one side of the PCB.
* Small errors in component placement are corrected automatically as the surface tension of molten solder pulls components into alignment with solder pads. (On the other hand, through-hole components cannot be slightly misaligned, because once the leads are through the holes, the components are fully aligned and cannot move laterally out of alignment.)
* Better mechanical performance under shock and vibration conditions (partly due to lower mass, and partly due to less cantilevering)
* Lower resistance and inductance at the connection; consequently, fewer unwanted RF signal effects and better and more predictable high-frequency performance.
* Better
EMC performance (lower radiated emissions) due to the smaller radiation loop area (because of the smaller package) and the lesser lead inductance.
* Fewer holes need to be drilled. (Drilling PCBs is time-consuming and expensive.)
* Lower initial cost and time of setting up for mass production, using automated equipment.
* Simpler and faster automated assembly. Some placement machines are capable of placing more than 136,000 components per hour.
* Many SMT parts cost less than equivalent through-hole parts.
Disadvantages
* SMT may be unsuitable as the sole attachment method for components that are subject to frequent mechanical stress, such as connectors that are used to interface with external devices that are frequently attached and detached.
* SMDs' solder connections may be damaged by
potting compounds going through thermal cycling.
* Manual prototype assembly or component-level repair is more difficult and requires skilled operators and more expensive tools, due to the small sizes and lead spacings of many SMDs.
Handling of small SMT components can be difficult, requiring tweezers, unlike nearly all through-hole components. Whereas through-hole components will stay in place (under gravitational force) once inserted and can be mechanically secured prior to soldering by bending out two leads on the solder side of the board, SMDs are easily moved out of place by a touch of a soldering iron. Without developed skill, when manually soldering or desoldering a component, it is easy to accidentally reflow the solder of an adjacent SMT component and unintentionally displace it, something that is almost impossible to do with through-hole components.
* Many types of SMT component packages cannot be installed in sockets, which provide for easy installation or exchange of components to modify a circuit and easy replacement of failed components. (Virtually all through-hole components can be socketed.)
* SMDs cannot be used directly with plug-in
breadboards (a quick snap-and-play prototyping tool), requiring either a custom PCB for every prototype or the mounting of the SMD upon a pin-leaded carrier. For prototyping around a specific SMD component, a less-expensive
breakout board may be used. Additionally,
stripboard
Stripboard is the generic name for a widely used type of electronics prototyping material for circuit boards characterized by a pre-formed regular (rectangular) grid of holes, with wide parallel strips of copper cladding running in one direct ...
style protoboards can be used, some of which include pads for standard sized SMD components. For prototyping, "
dead bug" breadboarding can be used.
* Solder joint dimensions in SMT quickly become much smaller as advances are made toward ultra-fine pitch technology. The reliability of solder joints becomes more of a concern, as less and less solder is allowed for each joint. Voiding is a fault commonly associated with solder joints, especially when reflowing a solder paste in the SMT application. The presence of voids can deteriorate the joint strength and eventually lead to joint failure.
* SMDs, usually being smaller than equivalent through-hole components, have less surface area for marking, requiring marked part ID codes or component values to be more cryptic and smaller, often requiring magnification to be read, whereas a larger through-hole component could be read and identified by the unaided eye. This is a disadvantage for prototyping, repair, rework, reverse engineering, and possibly for production set-up.
Rework
![Soldering a 0805](https://upload.wikimedia.org/wikipedia/commons/f/f8/Soldering_a_0805.jpg)
Defective surface-mount components can be repaired by using
soldering iron
A soldering iron is a hand tool used in soldering. It supplies heat to melt solder so that it can flow into the joint between two workpieces.
A soldering iron is composed of a heated metal tip (the ''bit'') and an insulated handle. Heating ...
s (for some connections), or using a non-contact rework system. In most cases a rework system is the better choice because SMD work with a soldering iron requires considerable skill and is not always feasible.
Reworking usually corrects some type of error, either human- or machine-generated, and includes the following steps:
* Melt solder and remove component(s)
* Remove residual solder (may be not required for some components)
* Print solder paste on PCB, directly or by dispensing or dipping
* Place new component and reflow.
Sometimes hundreds or thousands of the same part need to be repaired. Such errors, if due to assembly, are often caught during the process. However, a whole new level of rework arises when component failure is discovered too late, and perhaps unnoticed until the end user of the device being manufactured experiences it. Rework can also be used if products of sufficient value to justify it require revision or re-engineering, perhaps to change a single firmware-based component. Reworking in large volume requires an operation designed for that purpose.
There are essentially two non-contact soldering/desoldering methods: infrared soldering and soldering with hot gas.
Infrared
With infrared soldering, the energy for heating up the solder joint is transmitted by long-, medium- or short-wave infrared electromagnetic radiation.
Advantages:
* Easy setup
* No compressed air required for the heating process (some systems use compressed air for cooling)
* No requirement for different nozzles for many component shapes and sizes, reducing cost and the need to change nozzles
* Very uniform heating possible, assuming high quality IR heating systems
* Gentle reflow process with low surface temperatures, assuming correct profile settings
* Fast reaction of infrared source (depends on system used)
* Closed loop temperature control directly on the component possible by applied thermocouple or pyrometric measurement. This allows compensation of varying environmental influences and temperature losses. Enables use of the same temperature profile on slightly different assemblies, as the heating process adapts itself automatically. Enables (re)entry into the profile even on hot assemblies
* Direct setting of target profile temperatures and gradients possible through direct control of component temperature in each individual soldering process.
* No increased oxidation due to strong blowing of the solder joints with hot air, reduces flux wear or flux blowing away
* Documentation of the temperature elapsed on the component for each individual rework process possible
Disadvantages:
* Temperature sensitive nearby components must be shielded from heat to prevent damage, which requires additional time for every board
* On short wavelenght IR only: Surface temperature depends on the component's
albedo
Albedo (; ) is the measure of the diffuse reflection of solar radiation out of the total solar radiation and measured on a scale from 0, corresponding to a black body that absorbs all incident radiation, to 1, corresponding to a body that refl ...
: dark surfaces will be heated more than lighter surfaces
* Convective loss of energy at the component possible
* No reflow atmosphere possible (but also not required)
Hot gas
During hot gas soldering, the energy for heating up the solder joint is transmitted by a hot gas. This can be air or inert gas (
nitrogen
Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
).
Advantages:
* Some systems allow switching between hot air and nitrogen
* Standard and component-specific nozzles allow high reliability and faster processing
* Allow reproducible soldering profiles (depends on system used)
* Efficient heating, large amounts of heat can be transferred
* Even heating of the affected board area (depends on system / nozzle quality used)
* Temperature of the component will never exceed the adjusted gas temperature
* Rapid cooling after reflow, resulting in small-grained solder joints (depends on system used)
Disadvantages:
* Thermal capacity of the heat generator results in slow reaction whereby thermal profiles can be distorted (depends on system used)
* Precise, sometimes very complex, component-specific hot gas nozzles are needed to direct the hot gas to the target component. These can be very expensive.
* Today, nozzles can often no longer be deposited on the PCB by neighboring components, which means that there is no longer a closed process chamber and adjacent components can be blown on strongly from the side. This can lead to the blowing of adjacent components and even to thermal damage. In this case, adjacent components must be protected from the air flow, e.g. by covering them with polyimide tape.
* Local turbulence of the hot gas can create hot and cold spots on the heated surfaces, resulting in uneven heating. Perfectly designed, high-quality nozzles are therefore a must!
* Swirls at component edges, especially at bases and connectors, can heat these edges significantly more than other surfaces. Overheating can occur (burns, melting of plastics)
* Losses due to environmental influences are not compensated for, since the component temperature is not measured in the production process
* Creation of a suitable reflow profile requires an adjustment and test phase, in some cases involving several stages
* A direct temperature control of the component is not possible, because the measurement of the actual component temperature is difficult due to the high gas velocity (measurement failure!)
Hybrid technology
Hybrid rework systems combine medium-wave infrared radiation with hot air
Advantages:
* Easy setup
* The low flow velocity hot air supporting the IR radiation improves heat transfer, but cannot blow away components
* Heat transfer does not depend entirely on the flow velocity of hot gas at the component/assembly surface (see hot gas)
* No requirement for different nozzles for many component shapes and sizes, reducing cost and the need to change nozzles
* Adjustment of the heating surface possible through various attachments if required
* Heating even very large / long and exotically shaped components possible, depending on the type of top heater
* Very uniform heating possible, assuming high quality hybrid heating systems
* Gentle reflow process with low surface temperatures, assuming correct profile settings
* No compressed air required for the heating process (some systems use compressed air for cooling)
* Closed loop temperature control directly on the component possible by applied thermocouple or pyrometric measurement. This allows compensation of varying environmental influences and temperature losses. Enables use of the same temperature profile on slightly different assemblies, as the heating process adapts itself automatically. Enables (re)entry into the profile even on hot assemblies
* Direct setting of target profile temperatures and gradients possible through direct control of component temperature in each individual soldering process.
* No increased oxidation due to strong blowing of the solder joints with hot air, reduces flux wear or flux blowing away
* Documentation of the temperature elapsed on the component for each individual rework process possible
Disadvantages
* Temperature sensitive nearby components must be shielded from heat to prevent damage, which requires additional time for every board. Shield must cover also from gas flow
* Convective loss of energy at the component possible
Packages
![SMT sizes, based on original by Zureks](https://upload.wikimedia.org/wikipedia/commons/3/34/SMT_sizes%2C_based_on_original_by_Zureks.svg)
Surface-mount components are usually smaller than their counterparts with leads, and are designed to be handled by machines rather than by humans. The electronics industry has standardized package shapes and sizes (the leading standardisation body is
JEDEC
The JEDEC Solid State Technology Association is an independent semiconductor engineering trade organization and standardization body headquartered in Arlington County, Virginia, United States.
JEDEC has over 300 members, including some of the w ...
).
Identification
; Resistors: For 5% precision SMD resistors usually are marked with their resistance values using three digits: two significant digits and a multiplier digit. These are quite often white lettering on a black background, but other colored backgrounds and lettering can be used. For 1% precision SMD resistors, the code is used, as three digits would otherwise not convey enough information. This code consists of two digits and a letter: the digits denote the value's position in the
E96 Series
The E series is a system of preferred numbers (also called preferred values) derived for use in electronic components. It consists of the E3, E6, E12, E24, E48, E96 and E192 series, where the number after the 'E' designates the quantity of ...
of values, while the letter indicates the multiplier.
; Capacitors: Non-electrolytic capacitors are usually unmarked and the only reliable method of determining their value is removal from the circuit and subsequent measurement with a capacitance meter or impedance bridge. The materials used to fabricate the capacitors, such as nickel tantalate, possess different colours and these can give an approximate idea of the capacitance of the component. Generally physical size is proportional to capacitance and (squared) voltage for the same dielectric. For example, a 100 nF, 50 V capacitor may come in the same package as a 10 nF, 150 V device. SMD (non-electrolytic) capacitors, which are usually monolithic ceramic capacitors, exhibit the same body color on all four faces not covered by the end caps. SMD electrolytic capacitors, usually tantalum capacitors, and
film capacitor
Film capacitors, plastic film capacitors, film dielectric capacitors, or polymer film capacitors, generically called film caps as well as power film capacitors, are electrical capacitors with an insulating plastic film as the dielectric, sometime ...
s are marked like resistors, with two significant figures and a multiplier in units of picofarads or pF, (10
−12 farad.)
; Inductors: Smaller inductance with moderately high current ratings are usually of the ferrite bead type. They are simply a metal conductor looped through a ferrite bead and almost the same as their through-hole versions but possess SMD end caps rather than leads. They appear dark grey and are magnetic, unlike capacitors with a similar dark grey appearance. These ferrite bead type are limited to small values in the
nanohenry
The henry (symbol: H) is the unit of electrical inductance in the International System of Units (SI). If a current of 1 ampere flowing through a coil produces flux linkage of 1 weber turn, that coil has a self inductance of 1 henry. The unit ...
(nH) range and are often used as power supply rail decouplers or in high frequency parts of a circuit. Larger inductors and transformers may of course be through-hole mounted on the same board. SMT inductors with larger inductance values often have turns of wire or flat strap around the body or embedded in clear epoxy, allowing the wire or strap to be seen. Sometimes a
ferrite core
In electronics, a ferrite core is a type of magnetic core made of ferrite on which the windings of electric transformers and other wound components such as inductors are formed. It is used for its properties of high magnetic permeability couple ...
is present also. These higher inductance types are often limited to small current ratings, although some of the flat strap types can handle a few amps. As with capacitors, component values and identifiers for smaller inductors are not usually marked on the component itself; if not documented or printed on the PCB, measurement, usually removed from the circuit, is the only way of determining them. Larger inductors, especially wire-wound types in larger footprints, usually have the value printed on the top. For example, "330", which equates to a value of 33
μH.
; Discrete semiconductors: Discrete semiconductors, such as diodes and transistors are often marked with a two- or three-symbol code. The same code marked on different packages or on devices from different manufacturers can translate to different devices. Many of these codes, used because the devices are too small to be marked with more traditional numbers used on larger packages, correlate to more familiar traditional part numbers when a correlation list is consulted. GM4PMK in the United Kingdom has prepared
correlation list and
similar .pdf listis also available, although these lists are not complete.
; Integrated circuits: Generally, integrated circuit packages are large enough to be imprinted with the complete part number which includes the manufacturer's specific prefix, or a significant segment of the part number and the manufacturer's name or
logo
A logo (abbreviation of logotype; ) is a graphic mark, emblem, or symbol used to aid and promote public identification and recognition. It may be of an abstract or figurative design or include the text of the name it represents as in a wordma ...
.
See also
*
Board-to-board connector Board-to-board (BTB) connectors are used to connect printed circuit boards (PCB), electronic components that contain a conductive pattern printed on the surface of the insulating base in an accurate and repeatable manner. Each terminal on a BTB conn ...
s
*
Chip carrier
*
Electronics
The field of electronics is a branch of physics and electrical engineering that deals with the emission, behaviour and effects of electrons using electronic devices. Electronics uses active devices to control electron flow by amplification ...
*
Electronics manufacturing services
*
List of electronics package dimensions
Integrated circuits are put into protective packages to allow easy handling and assembly onto printed circuit boards and to protect the devices from damage. A very large number of different types of package exist. Some package types have standa ...
*
List of integrated circuit packaging types
Integrated circuits are put into protective packages to allow easy handling and assembly onto printed circuit boards and to protect the devices from damage. A very large number of different types of package exist. Some package types have stand ...
*
Plastic leaded chip carrier
In electronics, a chip carrier is one of several kinds of surface-mount technology packages for integrated circuits (commonly called "chips"). Connections are made on all four edges of a square package; compared to the internal cavity for mount ...
*
Point-to-point construction
Point-to-point construction is a non-automated method of construction of electronics Electronic circuit, circuits widely used before the use of printed circuit boards (PCBs) and automated assembly gradually became widespread following their intr ...
*
Printed circuit board
A printed circuit board (PCB; also printed wiring board or PWB) is a medium used in Electrical engineering, electrical and electronic engineering to connect electronic components to one another in a controlled manner. It takes the form of a L ...
*
RoHS
The Restriction of Hazardous Substances Directive 2002/95/EC (RoHS 1), short for Directive on the restriction of the use of certain hazardous substances in electrical and electronic equipment, was adopted in February 2003 by the European Unio ...
*
SMT placement equipment
Surface-mount technology (SMT) component placement systems, commonly called pick-and-place machines or P&Ps, are robotic machines which are used to place surface-mount devices (SMDs) onto a printed circuit board (PCB). They are used for high ...
*
Through-hole technology
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 ...
*
Wire wrap
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 l ...
*
RKM code
The RKM code, also referred to as "letter and numeral code for resistance and capacitance values and tolerances", "letter and digit code for resistance and capacitance values and tolerances", or informally as "R notation" is a notation to speci ...
References
{{Electronic components
Chip carriers
Electronic design
Electronics manufacturing
de:Surface-mounted device