A printed circuit board (PCB) mechanically supports and electrically
connects electronic components or electrical components using
conductive tracks, pads and other features etched from one or more
sheet layers of copper laminated onto and/or between sheet layers of a
non-conductive substrate. Components are generally soldered onto the
PCB to both electrically connect and mechanically fasten them to it.
Printed circuit boards are used in all but the simplest electronic
products. They are also used in some electrical products, such as
passive switch boxes.
Alternatives to PCBs include wire wrap and point-to-point
construction, both once popular but now rarely used. PCBs require
additional design effort to lay out the circuit, but manufacturing and
assembly can be automated. Specialized CAD software is available to do
much of the work of layout. Mass-producing circuits with PCBs is
cheaper and faster than with other wiring methods, as components are
mounted and wired in one operation. Large numbers of PCBs can be
fabricated at the same time, and the layout only has to be done once.
PCBs can also be made manually in small quantities, with reduced
PCBs can be single-sided (one copper layer), double-sided (two copper
layers on both sides of one substrate layer), or multi-layer (outer
and inner layers of copper, alternating with layers of substrate).
Multi-layer PCBs allow for much higher component density, because
circuit traces on the inner layers would otherwise take up surface
space between components. The rise in popularity of multilayer PCBs
with more than two, and especially with more than four, copper planes
was concurrent with the adoption of surface mount technology. However,
multilayer PCBs make repair, analysis, and field modification of
circuits much more difficult and usually impractical.
The world market for bare PCBs exceeded $60.2 billion in 2014.
3.1 Through-hole technology
3.2 Surface-mount technology
3.3 Circuit properties of the PCB
3.4.2 Key substrate parameters
3.4.3 Common substrates
3.4.5 Safety certification (US)
5.1 PCB CAM
5.3.1 Large volume
5.3.2 Small volume
5.4 Subtractive, additive and semi-additive processes
5.5 Chemical etching
Plating and coating
Solder resist application
5.10 Legend printing
5.11 Bare-board test
5.13 Protection and packaging
6 Cordwood construction
7 Multiwire boards
8 See also
10 External links
Before the development of printed circuit boards electrical and
electronic circuits were wired point-to-point on a chassis. Typically,
the chassis was a sheet metal frame or pan, sometimes with a wooden
bottom. Components were attached to the chassis, usually by insulators
when the connecting point on the chassis was metal, and then their
leads were connected directly or with jumper wires by soldering, or
sometimes using crimp connectors, wire connector lugs on screw
terminals, or other methods. Circuits were large, bulky, heavy, and
relatively fragile (even discounting the breakable glass envelopes of
the vacuum tubes that were often included in the circuits), and
production was labor-intensive, so the products were expensive.
Development of the methods used in modern printed circuit boards
started early in the 20th century. In 1903, a German inventor, Albert
Hanson, described flat foil conductors laminated to an insulating
board, in multiple layers.
Thomas Edison experimented with chemical
methods of plating conductors onto linen paper in 1904. Arthur Berry
in 1913 patented a print-and-etch method in the UK, and in the United
States Max Schoop obtained a patent to flame-spray metal onto a
board through a patterned mask. Charles Ducas in 1927 patented a
method of electroplating circuit patterns.
The Austrian engineer
Paul Eisler invented the printed circuit as part
of a radio set while working in the UK around 1936. In 1941 a
multi-layer printed circuit was used in German magnetic influence
naval mines. Around 1943 the USA began to use the technology on a
large scale to make proximity fuses for use in World War II. After
the war, in 1948, the USA released the invention for commercial use.
Printed circuits did not become commonplace in consumer electronics
until the mid-1950s, after the Auto-Sembly process was developed by
the United States Army. At around the same time in the UK work along
similar lines was carried out by Geoffrey Dummer, then at the RRDE.
Even as circuit boards became available, the point-to-point chassis
construction method remained in common use in industry (such as TV and
hi-fi sets) into at least the late 1960s. Printed circuit boards were
introduced to reduce the size, weight, and cost of parts of the
circuitry. In 1960, a small consumer radio receiver might be built
with all its circuitry on one circuit board, but a TV set would
probably contain one or more circuit boards.
An example of hand-drawn etched traces on a PCB
Predating the printed circuit invention, and similar in spirit, was
John Sargrove's 1936–1947 Electronic Circuit Making Equipment (ECME)
which sprayed metal onto a
Bakelite plastic board. The ECME could
produce three radio boards per minute.
During World War II, the development of the anti-aircraft proximity
fuse required an electronic circuit that could withstand being fired
from a gun, and could be produced in quantity. The Centralab Division
of Globe Union submitted a proposal which met the requirements: a
ceramic plate would be screenprinted with metallic paint for
conductors and carbon material for resistors, with ceramic disc
capacitors and subminiature vacuum tubes soldered in place. The
technique proved viable, and the resulting patent on the process,
which was classified by the U.S. Army, was assigned to Globe Union. It
was not until 1984 that the Institute of
Electrical and Electronics
Engineers (IEEE) awarded Mr. Harry W. Rubinstein the Cledo Brunetti
Award for early key contributions to the development of printed
components and conductors on a common insulating substrate. Mr.
Rubinstein was honored in 1984 by his alma mater, the University of
Wisconsin-Madison, for his innovations in the technology of printed
electronic circuits and the fabrication of capacitors. This
invention also represents a step in the development of integrated
circuit technology, as not only wiring but also passive components
were fabricated on the ceramic substrate.
A PCB as a design on a computer (left) and realized as a board
assembly populated with components (right). The board is double sided,
with through-hole plating, green solder resist and a white legend.
Both surface mount and through-hole components have been used.
Originally, every electronic component had wire leads, and a PCB had
holes drilled for each wire of each component. The component leads
were then inserted through the holes and soldered to the copper PCB
traces. This method of assembly is called through-hole construction.
In 1949, Moe Abramson and Stanislaus F. Danko of the United States
Army Signal Corps developed the Auto-Sembly process in which component
leads were inserted into a copper foil interconnection pattern and dip
soldered. The patent they obtained in 1956 was assigned to the U.S.
Army. With the development of board lamination and etching
techniques, this concept evolved into the standard printed circuit
board fabrication process in use today.
Soldering could be done
automatically by passing the board over a ripple, or wave, of molten
solder in a wave-soldering machine. However, the wires and holes are
inefficient since drilling holes is expensive and consumes drill bits
and the protruding wires are cut off and discarded.
From the 1980s onward, small surface mount parts have been used
increasingly instead of through-hole components; this has led to
smaller boards for a given functionality and lower production costs,
but with some additional difficulty in servicing faulty boards.
Manufacturers may not support component-level repair of printed
circuit boards because of the relatively low cost to replace compared
with the time and cost of troubleshooting to a component level. In
board-level repair, the technician identifies the board (PCA) on which
the fault resides and replaces it. This shift is economically
efficient from a manufacturer's point of view but is also materially
wasteful, as a circuit board with hundreds of good components may be
discarded and replaced due to the failure of one minor and inexpensive
part such as a resistor or capacitor. This practice is a significant
contributor to the problem of e-waste.
A basic PCB consists of a flat sheet of insulating material and a
layer of copper foil, laminated to the substrate. Chemical etching
divides the copper into separate conducting lines called tracks or
circuit traces, pads for connections, vias to pass connections between
layers of copper, and features such as solid conductive areas for EM
shielding or other purposes. The tracks function as wires fixed in
place, and are insulated from each other by air and the board
substrate material. The surface of a PCB may have a coating that
protects the copper from corrosion and reduces the chances of solder
shorts between traces or undesired electrical contact with stray bare
wires. For its function in helping to prevent solder shorts, the
coating is called solder resist.
A printed circuit board can have multiple copper layers. A two-layer
board has copper on both sides; multi layer boards sandwich additional
copper layers between layers of insulating material. Conductors on
different layers are connected with vias, which are copper-plated
holes that function as electrical tunnels through the insulating
substrate. Through-hole component leads sometimes also effectively
function as vias. After two-layer PCBs, the next step up is usually
four-layer. Often two layers are dedicated as power supply and ground
planes, and the other two are used for signal wiring between
"Through hole" components are mounted by their wire leads passing
through the board and soldered to traces on the other side. "Surface
mount" components are attached by their leads to copper traces on the
same side of the board. A board may use both methods for mounting
components. PCBs with only through-hole mounted components are now
uncommon. Surface mounting is used for transistors, diodes, IC chips,
resistors and capacitors. Through-hole mounting may be used for some
large components such as electrolytic capacitors and connectors.
The pattern to be etched into each copper layer of a PCB is called the
"artwork". The etching is usually done using photoresist which is
coated onto the PCB, then exposed to light projected in the pattern of
the artwork. The resist material protects the copper from dissolution
into the etching solution. The etched board is then cleaned. A PCB
design can be mass-reproduced in a way similar to the way photographs
can be mass-duplicated from film negatives using a photographic
In multi-layer boards, the layers of material are laminated together
in an alternating sandwich: copper, substrate, copper, substrate,
copper, etc.; each plane of copper is etched, and any internal vias
(that will not extend to both outer surfaces of the finished
multilayer board) are plated-through, before the layers are laminated
together. Only the outer layers need be coated; the inner copper
layers are protected by the adjacent substrate layers.
FR-4 glass epoxy is the most common insulating substrate. Another
substrate material is cotton paper impregnated with phenolic resin,
often tan or brown.
When a PCB has no components installed, it is less ambiguously called
a printed wiring board (PWB) or etched wiring board. However, the term
"printed wiring board" has fallen into disuse. A PCB populated with
electronic components is called a printed circuit assembly (PCA),
printed circuit board assembly or PCB assembly (PCBA). In informal
usage, the term "printed circuit board" most commonly means "printed
circuit assembly" (with components). The IPC preferred term for
assembled boards is circuit card assembly (CCA), and for assembled
backplanes it is backplane assemblies. "Card" is another widely used
informal term for a "printed circuit assembly".
A PCB may be "silkscreen" printed with a legend identifying the
components, test points, or identifying text. Originally, an actual
silkscreen printing process was used for this purpose, but today
other, finer quality printing methods are usually used instead.
Normally the screen printing is not significant to the function of the
A minimal PCB for a single component, used for prototyping, is called
a breakout board. The purpose of a breakout board is to "break out"
the leads of a component on separate terminals so that manual
connections to them can be made easily. Breakout boards are especially
used for surface-mount components or any components with fine lead
Advanced PCBs may contain components embedded in the
Main article: Through-hole technology
Through-hole (leaded) resistors
The first PCBs used through-hole technology, mounting electronic
components by leads inserted through holes on one side of the board
and soldered onto copper traces on the other side. Boards may be
single-sided, with an unplated component side, or more compact
double-sided boards, with components soldered on both sides.
Horizontal installation of through-hole parts with two axial leads
(such as resistors, capacitors, and diodes) is done by bending the
leads 90 degrees in the same direction, inserting the part in the
board (often bending leads located on the back of the board in
opposite directions to improve the part's mechanical strength),
soldering the leads, and trimming off the ends. Leads may be soldered
either manually or by a wave soldering machine.
Through-hole manufacture adds to board cost by requiring many holes to
be drilled accurately, and it limits the available routing area for
signal traces on layers immediately below the top layer on multi-layer
boards, since the holes must pass through all layers to the opposite
side. Once surface-mounting came into use, small-sized SMD components
were used where possible, with through-hole mounting only of
components unsuitably large for surface-mounting due to power
requirements or mechanical limitations, or subject to mechanical
stress which might damage the PCB (e.g. by lifting the copper off the
board surface).
Through-hole devices mounted on the circuit board of a mid-1980s home
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. Drilling is a considerable part of the cost of a through-hole
printed circuit board.
Main article: Surface-mount technology
Surface mount components, including resistors, transistors and an
Surface-mount technology emerged in the 1960s, gained momentum in the
early 1980s and became widely used by the mid-1990s. Components were
mechanically redesigned to have small metal tabs or end caps that
could be soldered directly onto the PCB surface, instead of wire leads
to pass through holes. Components became much smaller and component
placement on both sides of the board became more common than with
through-hole mounting, allowing much smaller PCB assemblies with much
higher circuit densities. Surface mounting lends itself well to a high
degree of automation, reducing labor costs and greatly increasing
production rates. Components can be supplied mounted on carrier tapes.
Surface mount components can be about one-quarter to one-tenth of the
size and weight of through-hole components, and passive components
much cheaper. However, prices of semiconductor surface mount devices
(SMDs) are determined more by the chip itself than the package, with
little price advantage over larger packages, and some wire-ended
components, such as 1N4148 small-signal switch diodes, are actually
significantly cheaper than SMD equivalents.
A PCB in a computer mouse: the component side (left) and the printed
Circuit properties of the PCB
Each trace consists of a flat, narrow part of the copper foil that
remains after etching. Its resistance, determined by its width,
thickness, and length, must be sufficiently low for the current the
conductor will carry. Power and ground traces may need to be wider
than signal traces. In a multi-layer board one entire layer may be
mostly solid copper to act as a ground plane for shielding and power
return. For microwave circuits, transmission lines can be laid out in
a planar form such as stripline or microstrip with carefully
controlled dimensions to assure a consistent impedance. In
radio-frequency and fast switching circuits the inductance and
capacitance of the printed circuit board conductors become significant
circuit elements, usually undesired; conversely, they can be used as a
deliberate part of the circuit design, obviating the need for
additional discrete components.
Laminates are manufactured by curing under pressure and temperature
layers of cloth or paper with thermoset resin to form an integral
final piece of uniform thickness. The size can be up to 4 by 8 feet
(1.2 by 2.4 m) in width and length. Varying cloth weaves (threads
per inch or cm), cloth thickness, and resin percentage are used to
achieve the desired final thickness and dielectric characteristics.
Available standard laminate thickness are listed in
The cloth or fiber material used, resin material, and the cloth to
resin ratio determine the laminate's type designation (FR-4, CEM-1,
G-10, etc.) and therefore the characteristics of the laminate
produced. Important characteristics are the level to which the
laminate is fire retardant, the dielectric constant (er), the loss
factor (tδ), the tensile strength, the shear strength, the glass
transition temperature (Tg), and the Z-axis expansion coefficient (how
much the thickness changes with temperature).
There are quite a few different dielectrics that can be chosen to
provide different insulating values depending on the requirements of
the circuit. Some of these dielectrics are polytetrafluoroethylene
(Teflon), FR-4, FR-1, CEM-1 or CEM-3. Well known pre-preg materials
used in the PCB industry are
FR-2 (phenolic cotton paper), FR-3
(cotton paper and epoxy),
FR-4 (woven glass and epoxy), FR-5 (woven
glass and epoxy), FR-6 (matte glass and polyester), G-10 (woven glass
and epoxy), CEM-1 (cotton paper and epoxy), CEM-2 (cotton paper and
epoxy), CEM-3 (non-woven glass and epoxy), CEM-4 (woven glass and
epoxy), CEM-5 (woven glass and polyester).
Thermal expansion is an
important consideration especially with ball grid array (BGA) and
naked die technologies, and glass fiber offers the best dimensional
FR-4 is by far the most common material used today. The board stock
with unetched copper on it is called "copper-clad laminate".
With decreasing size of board features and increasing frequencies,
small nonhomogeneities like uneven distribution of fiberglass or other
filler, thickness variations, and bubbles in the resin matrix, and the
associated local variations in the dielectric constant, are gaining
Key substrate parameters
The circuitboard substrates are usually dielectric composite
materials. The composites contain a matrix (usually an epoxy resin)
and a reinforcement (usually a woven, sometimes nonwoven, glass
fibers, sometimes even paper), and in some cases a filler is added to
the resin (e.g. ceramics; titanate ceramics can be used to increase
the dielectric constant).
The reinforcement type defines two major classes of materials: woven
and non-woven. Woven reinforcements are cheaper, but the high
dielectric constant of glass may not be favorable for many
higher-frequency applications. The spatially nonhomogeneous structure
also introduces local variations in electrical parameters, due to
different resin/glass ratio at different areas of the weave pattern.
Nonwoven reinforcements, or materials with low or no reinforcement,
are more expensive but more suitable for some RF/analog applications.
The substrates are characterized by several key parameters, chiefly
thermomechanical (glass transition temperature, tensile strength,
shear strength, thermal expansion), electrical (dielectric constant,
loss tangent, dielectric breakdown voltage, leakage current, tracking
resistance...), and others (e.g. moisture absorption).
At the glass transition temperature the resin in the composite softens
and significantly increases thermal expansion; exceeding Tg then
exerts mechanical overload on the board components - e.g. the joints
and the vias. Below Tg the thermal expansion of the resin roughly
matches copper and glass, above it gets significantly higher. As the
reinforcement and copper confine the board along the plane, virtually
all volume expansion projects to the thickness and stresses the
plated-through holes. Repeated soldering or other exposition to higher
temperatures can cause failure of the plating, especially with thicker
boards; thick boards therefore require a matrix with a high Tg.
The materials used determine the substrate's dielectric constant. This
constant is also dependent on frequency, usually decreasing with
frequency. As this constant determines the signal propagation speed,
frequency dependence introduces phase distortion in wideband
applications; as flat a dielectric constant vs frequency
characteristics as is achievable is important here. The impedance of
transmission lines decreases with frequency, therefore faster edges of
signals reflect more than slower ones.
Dielectric breakdown voltage determines the maximum voltage gradient
the material can be subjected to before suffering a breakdown
(conduction, or arcing, through the dielectric).
Tracking resistance determines how the material resists high voltage
electrical discharges creeping over the board surface.
Loss tangent determines how much of the electromagnetic energy from
the signals in the conductors is absorbed in the board material. This
factor is important for high frequencies. Low-loss materials are more
expensive. Choosing unnecessarily low-loss material is a common
engineering error in high-frequency digital design; it increases the
cost of the boards without a corresponding benefit. Signal degradation
by loss tangent and dielectric constant can be easily assessed by an
Moisture absorption occurs when the material is exposed to high
humidity or water. Both the resin and the reinforcement may absorb
water; water also may be soaked by capillary forces through voids in
the materials and along the reinforcement. Epoxies of the FR-4
materials aren't too susceptible, with absorption of only 0.15%.
Teflon has very low absorption of 0.01%. Polyimides and cyanate
esters, on the other side, suffer from high water absorption. Absorbed
water can lead to significant degradation of key parameters; it
impairs tracking resistance, breakdown voltage, and dielectric
parameters. Relative dielectric constant of water is about 73,
compared to about 4 for common circuit board materials. Absorbed
moisture can also vaporize on heating, as during soldering, and cause
cracking and delamination, the same effect responsible for
"popcorning" damage on wet packaging of electronic parts. Careful
baking of the substrates may be required to dry them prior to
Often encountered materials:
FR-2, phenolic paper or phenolic cotton paper, paper impregnated with
a phenol formaldehyde resin. Common in consumer electronics with
Electrical properties inferior to FR-4. Poor arc
resistance. Generally rated to 105 °C.
FR-4, a woven fiberglass cloth impregnated with an epoxy resin. Low
water absorption (up to about 0.15%), good insulation properties, good
arc resistance. Very common. Several grades with somewhat different
properties are available. Typically rated to 130 °C.
Aluminum, or metal core board or insulated metal substrate (IMS), clad
with thermally conductive thin dielectric - used for parts requiring
significant cooling - power switches, LEDs. Consists of usually
single, sometimes double layer thin circuit board based on e.g. FR-4,
laminated on aluminum sheet metal, commonly 0.8, 1, 1.5, 2 or
3 mm thick. The thicker laminates sometimes also come with
thicker copper metalization.
Flexible substrates - can be a standalone copper-clad foil or can be
laminated to a thin stiffener, e.g. 50-130 µm
Kapton or UPILEX, a polyimide foil. Used for flexible printed
circuits, in this form common in small form-factor consumer
electronics or for flexible interconnects. Resistant to high
Pyralux, a polyimide-fluoropolymer composite foil.
can delaminate during soldering.
Less-often encountered materials:
FR-1, like FR-2, typically specified to 105 °C, some grades
rated to 130 °C. Room-temperature punchable. Similar to
cardboard. Poor moisture resistance. Low arc resistance.
FR-3, cotton paper impregnated with epoxy. Typically rated to
FR-5, woven fiberglass and epoxy, high strength at higher
temperatures, typically specified to 170 °C.
FR-6, matte glass and polyester
G-10, woven glass and epoxy - high insulation resistance, low moisture
absorption, very high bond strength. Typically rated to 130 °C.
G-11, woven glass and epoxy - high resistance to solvents, high
flexural strength retention at high temperatures. Typically rated
to 170 °C.
CEM-1, cotton paper and epoxy
CEM-2, cotton paper and epoxy
CEM-3, non-woven glass and epoxy
CEM-4, woven glass and epoxy
CEM-5, woven glass and polyester
PTFE, ("Teflon") - expensive, low dielectric loss, for high frequency
applications, very low moisture absorption (0.01%), mechanically soft.
Difficult to laminate, rarely used in multilayer applications.
PTFE, ceramic filled - expensive, low dielectric loss, for high
frequency applications. Varying ceramics/
PTFE ratio allows adjusting
dielectric constant and thermal expansion.
RF-35, fiberglass-reinforced ceramics-filled PTFE. Relatively less
expensive, good mechanical properties, good high-frequency
Alumina, a ceramic. Hard, brittle, very expensive, very high
performance, good thermal conductivity.
Polyimide, a high-temperature polymer. Expensive, high-performance.
Higher water absorption (0.4%). Can be used from cryogenic
temperatures to over 260 °C.
Copper thickness of PCBs can be specified directly or as the weight of
copper per area (in ounce per square foot) which is easier to measure.
One ounce per square foot is 1.344 mils or 34 micrometers thickness.
Heavy copper is a layer exceeding three ounces of copper per ft2, or
approximately 0.0042 inches (4.2 mils, 105 μm) thick.
Heavy copper layers are used for high current or to help dissipate
On the common
FR-4 substrates, 1 oz copper per ft2 (35 µm) is
the most common thickness; 2 oz (70 µm) and 0.5 oz (18 µm)
thickness is often an option. Less common are 12 and 105 µm,
9 µm is sometimes available on some substrates. Flexible
substrates typically have thinner metalization. Metal-core boards for
high power devices commonly use thicker copper; 35 µm is usual
but also 140 and 400 µm can be encountered.
Safety certification (US)
Safety Standard UL 796 covers component safety requirements for
printed wiring boards for use as components in devices or appliances.
Testing analyzes characteristics such as flammability, maximum
operating temperature, electrical tracking, heat deflection, and
direct support of live electrical parts.
A board designed in 1967; the sweeping curves in the traces are
evidence of freehand design using adhesive tape
Initially PCBs were designed manually by creating a photomask on a
clear mylar sheet, usually at two or four times the true size.
Starting from the schematic diagram the component pin pads were laid
out on the mylar and then traces were routed to connect the pads.
Rub-on dry transfers of common component footprints increased
efficiency. Traces were made with self-adhesive tape. Pre-printed
non-reproducing grids on the mylar assisted in layout. The finished
photomask was photolithographically reproduced onto a photoresist
coating on the blank copper-clad boards.
Modern PCBs are designed with dedicated layout software, generally in
the following steps:
Schematic capture through an electronic design automation (EDA) tool.
Card dimensions and template are decided based on required circuitry
and case of the PCB.
The positions of the components and heat sinks are determined.
Layer stack of the PCB is decided, with one to tens of layers
depending on complexity. Ground and power planes are decided. A power
plane is the counterpart to a ground plane and behaves as an AC signal
ground while providing DC power to the circuits mounted on the PCB.
Signal interconnections are traced on signal planes. Signal planes can
be on the outer as well as inner layers. For optimal EMI performance
high frequency signals are routed in internal layers between power or
Line impedance is determined using dielectric layer thickness, routing
copper thickness and trace-width. Trace separation is also taken into
account in case of differential signals. Microstrip, stripline or dual
stripline can be used to route signals.
Components are placed. Thermal considerations and geometry are taken
into account. Vias and lands are marked.
Signal traces are routed.
Electronic design automation
Electronic design automation tools usually
create clearances and connections in power and ground planes
Gerber files are generated for manufacturing.
PCB manufacturing consists of many steps.
Manufacturing starts from the fabrication data generated by computer
aided design, and component information. The fabrication data is
read into the CAM (
Computer Aided Manufacturing) software. CAM
performs the following functions:
Input of the fabrication data.
Verification of the data
Compensation for deviations in the manufacturing processes (e.g.
scaling to compensate for distortions during lamination)
Output of the digital tools (copper patterns, drill files, inspection,
and others) 
Several small printed circuit boards (of the same or of different
designs) can be grouped together for processing as a panel. The
assemblers often mount components on panels rather than single PCBs
because this is efficient.
The panel is eventually broken into individual PCBs along perforations
or grooves in the panel. Today depaneling is often done by lasers
which cut the board with no contact.
Laser depaneling reduces stress
on the fragile circuits, improving the yield of defect-free units.
The first step is to replicate the pattern in the fabricator's CAM
system on a protective mask on the copper foil PCB layers. Subsequent
etching removes the unwanted copper. (Alternatively, a conductive ink
can be ink-jetted on a blank (non-conductive) board. This technique is
also used in the manufacture of hybrid circuits.)
Silk screen printing uses etch-resistant inks to create the protective
Photoengraving uses a photomask and developer to selectively remove a
UV-sensitive photoresist coating and thus create a photoresist mask.
Direct imaging techniques are sometimes used for high-resolution
requirements. Experiments were made with thermal resist.
PCB milling uses a two or three-axis mechanical milling system to mill
away the copper foil from the substrate. A PCB milling machine
(referred to as a 'PCB Prototyper') operates in a similar way to a
plotter, receiving commands from the host software that control the
position of the milling head in the x, y, and (if relevant) z axis.
Laser resist ablation Spray black paint onto copper clad laminate,
CNC laser plotter. The laser raster-scans the PCB and
ablates (vaporizes) the paint where no resist is wanted. (Note: laser
copper ablation is rarely used and is considered
The method chosen depends on the number of boards to be produced and
the required resolution.
Silk screen printing – Used for PCBs with bigger features
Photoengraving – Used when finer features are required
Print onto transparent film and use as photo mask along with
photo-sensitized boards, then etch. (Alternatively, use a film
Laser resist ablation
Laser-printed resist: Laser-print onto toner transfer paper,
heat-transfer with an iron or modified laminator onto bare laminate,
soak in water bath, touch up with a marker, then etch.
Vinyl film and resist, non-washable marker, some other methods.
Labor-intensive, only suitable for single boards.
Subtractive, additive and semi-additive processes
The two processing methods used to produce a double-sided PWB with
Subtractive methods remove copper from an entirely copper-coated board
to leave only the desired copper pattern. In additive methods the
pattern is electroplated onto a bare substrate using a complex
process. The advantage of the additive method is that less material is
needed and less waste is produced. In the full additive process the
bare laminate is covered with a photosensitive film which is imaged
(exposed to light through a mask and then developed which removes the
unexposed film). The exposed areas are sensitized in a chemical bath,
usually containing palladium and similar to that used for through hole
plating which makes the exposed area capable of bonding metal ions.
The laminate is then plated with copper in the sensitized areas. When
the mask is stripped, the PCB is finished.
Semi-additive is the most common process: The unpatterned board has a
thin layer of copper already on it. A reverse mask is then applied.
(Unlike a subtractive process mask, this mask exposes those parts of
the substrate that will eventually become the traces.) Additional
copper is then plated onto the board in the unmasked areas; copper may
be plated to any desired weight. Tin-lead or other surface platings
are then applied. The mask is stripped away and a brief etching step
removes the now-exposed bare original copper laminate from the board,
isolating the individual traces. Some single-sided boards which have
plated-through holes are made in this way.
General Electric made
consumer radio sets in the late 1960s using additive boards.
The (semi-)additive process is commonly used for multi-layer boards as
it facilitates the plating-through of the holes to produce conductive
vias in the circuit board.
PCB copper electroplating line in the process of pattern plating
PCBs in process of having copper pattern plated (note the blue dry
Chemical etching is usually done with ammonium persulfate or ferric
chloride. For PTH (plated-through holes), additional steps of
electroless deposition are done after the holes are drilled, then
copper is electroplated to build up the thickness, the boards are
screened, and plated with tin/lead. The tin/lead becomes the resist
leaving the bare copper to be etched away.
The simplest method, used for small-scale production and often by
hobbyists, is immersion etching, in which the board is submerged in
etching solution such as ferric chloride. Compared with methods used
for mass production, the etching time is long. Heat and agitation can
be applied to the bath to speed the etching rate. In bubble etching,
air is passed through the etchant bath to agitate the solution and
speed up etching. Splash etching uses a motor-driven paddle to splash
boards with etchant; the process has become commercially obsolete
since it is not as fast as spray etching. In spray etching, the
etchant solution is distributed over the boards by nozzles, and
recirculated by pumps. Adjustment of the nozzle pattern, flow rate,
temperature, and etchant composition gives predictable control of
etching rates and high production rates.
As more copper is consumed from the boards, the etchant becomes
saturated and less effective; different etchants have different
capacities for copper, with some as high as 150 grams of copper per
litre of solution. In commercial use, etchants can be regenerated to
restore their activity, and the dissolved copper recovered and sold.
Small-scale etching requires attention to disposal of used etchant,
which is corrosive and toxic due to its metal content.
The etchant removes copper on all surfaces exposed by the resist.
"Undercut" occurs when etchant attacks the thin edge of copper under
the resist; this can reduce conductor widths and cause open-circuits.
Careful control of etch time is required to prevent undercut. Where
metallic plating is used as a resist, it can "overhang" which can
cause short-circuits between adjacent traces when closely spaced.
Overhang can be removed by wire-brushing the board after etching.
Cut through a SDRAM-module, a multi-layer PCB. Note the via, visible
as a bright copper-colored band running between the top and bottom
layers of the board.
This section does not cite any sources. Please help improve this
section by adding citations to reliable sources. Unsourced material
may be challenged and removed. (October 2016) (Learn how and when to
remove this template message)
Multi-layer printed circuit boards have trace layers inside the board.
This is achieved by laminating a stack of materials in a press by
applying pressure and heat for a period of time. This results in an
inseparable one piece product. For example, a four-layer PCB can be
fabricated by starting from a two-sided copper-clad laminate, etch the
circuitry on both sides, then laminate to the top and bottom pre-preg
and copper foil. It is then drilled, plated, and etched again to get
traces on top and bottom layers.
The inner layers are given a complete machine inspection before
lamination because afterwards mistakes cannot be corrected. The
automatic optical inspection system compares an image of the board
with the digital image generated from the original design data.
Holes through a PCB are typically drilled with drill bits made of
solid coated tungsten carbide. Coated tungsten carbide is used because
board materials are abrasive. High-speed-steel bits would dull
quickly, tearing the copper and ruining the board. Drilling is done by
computer-controlled drilling machines, using a drill file or Excellon
file that describes the location and size of each drilled hole.
Holes may be made conductive, by electroplating or inserting hollow
metal eyelets, to connect board layers. Some conductive holes are
intended for the insertion of through-hole-component leads. Others
used to connect board layers, are called vias.
When very small vias are required, drilling with mechanical bits is
costly because of high rates of wear and breakage. In this case, the
vias may be laser drilled—evaporated by lasers. Laser-drilled
vias typically have an inferior surface finish inside the hole. These
holes are called micro vias.
It is also possible with controlled-depth drilling, laser drilling, or
by pre-drilling the individual sheets of the PCB before lamination, to
produce holes that connect only some of the copper layers, rather than
passing through the entire board. These holes are called blind vias
when they connect an internal copper layer to an outer layer, or
buried vias when they connect two or more internal copper layers and
no outer layers.
The hole walls for boards with two or more layers can be made
conductive and then electroplated with copper to form plated-through
holes. These holes electrically connect the conducting layers
of the PCB. For multi-layer boards, those with three layers or more,
drilling typically produces a smear of the high temperature
decomposition products of bonding agent in the laminate system. Before
the holes can be plated through, this smear must be removed by a
chemical de-smear process, or by plasma-etch. The de-smear process
ensures that a good connection is made to the copper layers when the
hole is plated through. On high reliability boards a process called
etch-back is performed chemically with a potassium permanganate based
etchant or plasma. The etch-back removes resin and the glass
fibers so that the copper layers extend into the hole and as the hole
is plated become integral with the deposited copper.
Plating and coating
Proper plating or surface finish selection can be critical to process
yield, the amount of rework, field failure rate, and
PCBs are plated with solder, tin, or gold over nickel and a resist for
etching away the unneeded underlying copper.
After PCBs are etched and then rinsed with water, the solder mask is
applied, and then any exposed copper is coated with solder,
nickel/gold, or some other anti-corrosion coating.
Matte solder is usually fused to provide a better bonding surface for
bare copper. Treatments, such as benzimidazolethiol, prevent surface
oxidation of bare copper. The places to which components will be
mounted are typically plated, because untreated bare copper oxidizes
quickly, and therefore is not readily solderable. Traditionally, any
exposed copper was coated with solder by hot air solder levelling
(HASL). The HASL finish prevents oxidation from the underlying copper,
thereby guaranteeing a solderable surface. This solder was a
tin-lead alloy, however new solder compounds are now used to achieve
compliance with the
RoHS directive in the EU, which restricts the use
of lead. One of these lead-free compounds is SN100CL, made up of 99.3%
tin, 0.7% copper, 0.05% nickel, and a nominal of 60 ppm
It is important to use solder compatible with both the PCB and the
parts used. An example is ball grid array (BGA) using tin-lead solder
balls for connections losing their balls on bare copper traces or
using lead-free solder paste.
Other platings used are OSP (organic surface protectant), immersion
silver (IAg), immersion tin, electroless nickel with immersion gold
coating (ENIG), electroless nickel electroless palladium immersion
gold (ENEPIG) and direct gold plating (over nickel). Edge connectors,
placed along one edge of some boards, are often nickel-plated then
gold-plated. Another coating consideration is rapid diffusion of
coating metal into tin solder.
Tin forms intermetallics such as Cu6Sn5
and Ag3Cu that dissolve into the
Tin liquidus or solidus(@50C),
stripping surface coating or leaving voids.
Electrochemical migration (ECM) is the growth of conductive metal
filaments on or in a printed circuit board (PCB) under the influence
of a DC voltage bias. Silver, zinc, and aluminum are known to
grow whiskers under the influence of an electric field. Silver also
grows conducting surface paths in the presence of halide and other
ions, making it a poor choice for electronics use.
Tin will grow
"whiskers" due to tension in the plated surface. Tin-lead or solder
plating also grows whiskers, only reduced by reducing the percentage
of tin. Reflow to melt solder or tin plate to relieve surface stress
lowers whisker incidence. Another coating issue is tin pest, the
transformation of tin to a powdery allotrope at low temperature.
Solder resist application
Areas that should not be soldered may be covered with solder resist
(solder mask). One of the most common solder resists used today is
called "LPI" (liquid photoimageable solder mask). A
photo-sensitive coating is applied to the surface of the PWB, then
exposed to light through the solder mask image film, and finally
developed where the unexposed areas are washed away. Dry film solder
mask is similar to the dry film used to image the PWB for plating or
etching. After being laminated to the PWB surface it is imaged and
developed as LPI. Once but no longer commonly used, because of its low
accuracy and resolution, is to screen print epoxy ink. In addition to
repelling solder, solder resist also provides protection from the
environment to the copper that would otherwise be exposed.
A legend is often printed on one or both sides of the PCB. It contains
the component designators, switch settings, test points and other
indications helpful in assembling, testing, servicing, and sometimes
using the circuit board.
There are three methods to print the legend.
Silk screen printing epoxy ink was the established method. It was so
common that legend is often misnamed silk or silkscreen.
Liquid photo imaging is a more accurate method than screen printing.
Ink jet printing is new but increasingly used. Ink jet can print
variable data, unique to each PWB unit, such as text or a bar code
with a serial number.
Boards with no components installed are usually bare-board tested for
"shorts" and "opens". A short is a connection between two points that
should not be connected. An open is a missing connection between
points that should be connected. For high-volume production, a fixture
or a rigid needle adapter makes contact with copper lands on the
board. The fixture or adapter is a significant fixed cost and this
method is only economical for high-volume or high-value production.
For small or medium volume production flying probe testers are used
where test probes are moved over the board by an XY drive to make
contact with the copper lands. There is no need for a fixture and
hence the fixed costs are much lower. The CAM system instructs the
electrical tester to apply a voltage to each contact point as required
and to check that this voltage appears on the appropriate contact
points and only on these.
PCB with test connection pads
In assembly the bare board is populated (or "stuffed") with electronic
components to form a functional printed circuit assembly (PCA),
sometimes called a "printed circuit board assembly" (PCBA). In
through-hole technology, the component leads are inserted in holes
surrounded by conductive pads; the holes keep the components in place.
In surface-mount technology (SMT), the component is placed on the PCB
so that the pins line up with the conductive pads or lands on the
surfaces of the PCB; solder paste, which was previously applied to the
pads, holds the components in place temporarily; if surface-mount
components are applied to both sides of the board, the bottom-side
components are glued to the board. In both through hole and surface
mount, the components are then soldered; once cooled and solidified,
the solder holds the components in place permanently and electrically
connects them to the board.
There are a variety of soldering techniques used to attach components
to a PCB. High volume production is usually done with a "Pick and
place machine" or SMT placement machine and bulk wave soldering or
reflow ovens, but skilled technicians are able to hand-solder very
tiny parts (for instance 0201 packages which are 0.02 in. by 0.01
in.) under a microscope, using tweezers and a fine-tip soldering
iron, for small volume prototypes. Some SMT parts cannot be soldered
by hand, such as BGA packages. All through-hole components can be hand
soldered, making them favored for prototyping where size, weight, and
the use of the exact components that would be used in high volume
production are not concerns.
Often, through-hole and surface-mount construction must be combined in
a single assembly because some required components are available only
in surface-mount packages, while others are available only in
through-hole packages. Or, even if all components are available in
through-hole packages, it might be desired to take advantage of the
size, weight, and cost reductions obtainable by using some available
surface-mount devices. Another reason to use both methods is that
through-hole mounting can provide needed strength for components
likely to endure physical stress (such as connectors that are
frequently mated and demated or that connect to cables expected to
impart substantial stress to the PCB-and-connector interface), while
components that are expected to go untouched will take up less space
using surface-mount techniques. For further comparison, see the SMT
After the board has been populated it may be tested in a variety of
While the power is off, visual inspection, automated optical
JEDEC guidelines for PCB component placement, soldering,
and inspection are commonly used to maintain quality control in this
stage of PCB manufacturing.
While the power is off, analog signature analysis, power-off testing.
While the power is on, in-circuit test, where physical measurements
(for example, voltage) can be done.
While the power is on, functional test, just checking if the PCB does
what it had been designed to do.
To facilitate these tests, PCBs may be designed with extra pads to
make temporary connections. Sometimes these pads must be isolated with
resistors. The in-circuit test may also exercise boundary scan test
features of some components.
In-circuit test systems may also be used
to program nonvolatile memory components on the board.
In boundary scan testing, test circuits integrated into various ICs on
the board form temporary connections between the PCB traces to test
that the ICs are mounted correctly.
Boundary scan testing requires
that all the ICs to be tested use a standard test configuration
procedure, the most common one being the Joint Test Action Group
(JTAG) standard. The
JTAG test architecture provides a means to test
interconnects between integrated circuits on a board without using
physical test probes, by using circuitry in the ICs to employ the IC
pins themselves as test probes.
JTAG tool vendors provide various
types of stimuli and sophisticated algorithms, not only to detect the
failing nets, but also to isolate the faults to specific nets,
devices, and pins.
When boards fail the test, technicians may desolder and replace failed
components, a task known as rework.
Protection and packaging
PCBs intended for extreme environments often have a conformal coating,
which is applied by dipping or spraying after the components have been
soldered. The coat prevents corrosion and leakage currents or shorting
due to condensation. The earliest conformal coats were wax; modern
conformal coats are usually dips of dilute solutions of silicone
rubber, polyurethane, acrylic, or epoxy. Another technique for
applying a conformal coating is for plastic to be sputtered onto the
PCB in a vacuum chamber. The chief disadvantage of conformal coatings
is that servicing of the board is rendered extremely difficult.
Many assembled PCBs are static sensitive, and therefore they must be
placed in antistatic bags during transport. When handling these
boards, the user must be grounded (earthed). Improper handling
techniques might transmit an accumulated static charge through the
board, damaging or destroying components. The damage might not
immediately affect function but might lead to early failure later on,
cause intermittent operating faults, or cause a narrowing of the range
of environmental and electrical conditions under which the board
functions properly. Even bare boards are sometimes static sensitive:
traces have become so fine that it's quite possible to blow an etch
off the board (or change its characteristics) with a static charge.
This is especially true on non-traditional PCBs such as MCMs and
This section needs additional citations for verification. Please help
improve this article by adding citations to reliable sources.
Unsourced material may be challenged and removed. (December 2016)
(Learn how and when to remove this template message)
A cordwood module
Cordwood construction was used in proximity fuzes.
Cordwood construction can save significant space and was often used
with wire-ended components in applications where space was at a
premium (such as fuzes, missile guidance, and telemetry systems) and
in high-speed computers, where short traces were important. In
cordwood construction, axial-leaded components were mounted between
two parallel planes. The components were either soldered together with
jumper wire, or they were connected to other components by thin nickel
ribbon welded at right angles onto the component leads. To avoid
shorting together different interconnection layers, thin insulating
cards were placed between them. Perforations or holes in the cards
allowed component leads to project through to the next interconnection
layer. One disadvantage of this system was that special nickel-leaded
components had to be used to allow the interconnecting welds to be
made. Differential thermal expansion of the component could put
pressure on the leads of the components and the PCB traces and cause
mechanical damage (as was seen in several modules on the Apollo
program). Additionally, components located in the interior are
difficult to replace. Some versions of cordwood construction used
soldered single-sided PCBs as the interconnection method (as
pictured), allowing the use of normal-leaded components.
Before the advent of integrated circuits, this method allowed the
highest possible component packing density; because of this, it was
used by a number of computer vendors including Control Data
Corporation. The cordwood method of construction was used only rarely
once semiconductor electronics and PCBs became widespread.
Multiwire is a patented technique of interconnection which uses
machine-routed insulated wires embedded in a non-conducting matrix
(often plastic resin). It was used during the 1980s and 1990s.
(Kollmorgen Technologies Corp, U.S. Patent 4,175,816 filed 1978) As of
2010, Multiwire was still available through Hitachi.
Since it was quite easy to stack interconnections (wires) inside the
embedding matrix, the approach allowed designers to forget completely
about the routing of wires (usually a time-consuming operation of PCB
design): Anywhere the designer needs a connection, the machine will
draw a wire in a straight line from one location/pin to another. This
led to very short design times (no complex algorithms to use even for
high density designs) as well as reduced crosstalk (which is worse
when wires run parallel to each other—which almost never happens in
Multiwire), though the cost is too high to compete with cheaper PCB
technologies when large quantities are needed.
Corrections can be made to a Multiwire board more easily than to a
There are other competitive discrete wiring technologies that have
Design for manufacturability (PCB)
Occam process – another process for the manufacturing of PCBs
Printed electronics – creation of components by printing
Printed circuit board
Printed circuit board milling
Composite epoxy material, CEM-1,5
FR-4, the most common PCB material
PCB layout software
List of EDA companies
Comparison of EDA software
^ "iconnect007 :: Article". www.iconnect007.com. Retrieved
^ US 1256599
^ a b Charles A. Harper, Electronic materials and processes handbook,
McGraw-Hill,2003 ISBN 0-07-140214-4, pages 7.3 and 7.4
^ Brunetti, Cledo (22 November 1948). New Advances in Printed
Circuits. Washington DC: National Bureau of Standards.
^ Engineers' Day, 1984 Award Recipients, College of Engineering,
University of Wisconsin-Madison
^ US 2756485 assigned to US Army. July 31, 1956.
^ "What is a Breakout Board for Arduino?".
^ 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
^ "Design Standard for Rigid Printed Boards and Rigid Printed Board
Assemblies". IPC. September 1991. IPC-4101.
^ Sood, B. and Pecht, M. 2011. Printed Circuit Board Laminates. Wiley
Encyclopedia of Composites. 1–11.
^ By Lee W. Ritchey, Speeding Edge (November 1999). "A SURVEY AND
TUTORIAL OF DIELECTRIC MATERIALS USED IN THE MANUFACTURE OF PRINTED
CIRCUIT BOARDS" (PDF). Circuitree magazine.
^ pcb-solutions.com Advantages of Using
Aluminum in Printed Circuit
^ "Applications UBE Heat Resistant
Polyimide Materials". UBE,
^ "Pyralux® Flexible Circuit Materials - DuPont - DuPont USA".
^ Carter, Bruce (19 March 2009). "Op Amps for Everyone". Newnes –
via Google Books.
^ "A High Performance, Economical RF/
^ "RF-35 datasheet" (PDF). Taconic – via Multi-CB.
^ Printed Circuit Board Design Flow Methodology
^ "See appendix D of IPC-2251" (PDF).
^ a b c d Tavernier, Karel. "PCB Fabrication Data - A Guide". Ucamco.
Retrieved 8 January 2015.
^ Vermeire, Filip. "PCB Fabrication Data Example 1". Ucamco. Ucamco.
Retrieved 7 January 2015.
^ Vermeire, Filip. "PCB Fabrication Data Example 2". Ucamco. Ucamco.
Retrieved 7 January 2015.
^ a b "The Gerber
File Format Specification". Ucamco. Retrieved 8
^ "Frontend data preparation". Eurocircuits. Retrieved 1 April
^ "Making a PCB - Educational movies". Eurocircuits. Eurocircuits.
Retrieved 20 January 2015.
^ Kraig Mitzner, Complete PCB Design Using OrCad Capture and Layout,
pages 443–446, Newnes, 2011 ISBN 0080549209.
^ Itshak Taff, Hai Benron. "Liquid Photoresists for Thermal Direct
Imaging". The Board Authority, October 1999. Missing or empty
url= (help)CS1 maint: Uses authors parameter (link)
^ Riley, Frank; Production, Electronic Packaging and (2013-06-29). The
Electronics Assembly Handbook. Springer Science & Business Media.
p. 285. ISBN 9783662131619.
^ a b R. S. Khandpur,Printed circuit boards: design, fabrication,
assembly and testing, Tata-McGraw Hill, 2005 ISBN 0-07-058814-7,
^ Bosshart (1983-01-01). Printed Circuit Boards: Design and
Technology. Tata McGraw-Hill Education. p. 298.
^ Chenxi (1 January 2016). "32 Layer Printed Circuit Boards".
www.wellpcb.com. Retrieved 2017-05-03.
^ "Inner layer inspection". Eurocircuits. Retrieved 31 Aug 2013.
Laser Drilling Orbotech". www.orbotech.com. Retrieved
^ Julia, lia (20 November 2011). "PCB assembly, PCB assembly quote,
Printed Circuit Board Assembly". www.ourpcb.com. OURPCB. Retrieved 29
^ Yash Sutariya, (May 2013); Microvia Fabrication: When to drill, When
to Blast, Alpha Circuit; Saturn Flex Systems
^ "Making Holes Conductive". Electronic Chemicals. Retrieved 5 Sep
^ "Electro-Brite E-Prep Desmear/Etchback". OM Group, Inc. Retrieved 5
^ "Considerations for Selecting a PCB Surface Finish" (PDF). 8 October
^ Appendix F Sample Fabrication Sequence for a Standard Printed
Circuit Board, Linkages: Manufacturing Trends in Electronics
Interconnection Technology, National Academy of Sciences
^ Production Methods and Materials 3.1 General Printed Wiring Board
Project Report – Table of Contents, Design for the Environment
(DfE), US EPA
^ George Milad and Don Gudeczauskas. "
Solder Joint Reliability of Gold
Surface Finishes (ENIG, ENEPIG and DIG) for PWB Assembled with Lead
Free SAC Alloy."
^ "Nickel/Gold tab plating line"
Soldering 101 – A Basic Overview".
^ IPC Publication IPC-TR-476A, "Electrochemical Migration:
Electrically Induced Failures in Printed Wiring Assemblies,"
Northbrook, IL, May 1997.
^ S.Zhan, M. H. Azarian and M. Pecht, "Reliability Issues of No-Clean
Flux Technology with Lead-free
Solder Alloy for High Density Printed
Circuit Boards", 38th International Symposium on Microelectronics, pp.
367–375, Philadelphia, PA, September 25–29, 2005.
^ Clyde F. Coombs Printed Circuits Handbook McGraw–Hill
Professional, 2007 ISBN 0-07-146734-3, pages 45–19
^ "liquid photoimageable solder masks" (PDF). Coates Circuit Products.
Retrieved 2 Sep 2012.
^ "Silk-screen and cure". Eurocircuits. Retrieved 31 Aug 2013.
^ "Towards a more rational silkscreen". Optimum Design Associates.
Retrieved 31 Aug 2013.
Electrical test". Eurocircuits. Retrieved 13 Apr 2015.
^ Ayob, M.; Kendall, G. (2008). "A Survey of Surface Mount Device
Placement Machine Optidmisation: Machine Classification". European
Journal of Operational Research. 186 (3): 893–914.
^ Ayob, M.; Kendall, G. (2005). "A Triple Objective Function with a
Chebychev Dynamic Pick-and-place Point Specification Approach to
Optimise the Surface Mount Placement Machine" (PDF). European Journal
of Operational Research. 164 (3): 609–626.
^ Borkes, Tom. "SMTA TechScan Compendium: 0201 Design, Assembly and
Process" (PDF). Surface Mount Technology Association. Retrieved
^ Shibu. Intro To Embedded Systems 1E. Tata McGraw-Hill. p. 293.
^ Wagner, G. Donald (1999). "History of Electronic Packaging at APL:
From the VT
Fuze to the NEAR Spacecraft" (PDF). Johns Hopkins APL
Technical Digest. 20 (1). Retrieved 2016-12-19.
^ David E. Weisberg. "Chapter 14: Intergraph". 2008. p. 14-8.
The Wikibook Practical Electronics has a page on the topic of: PCB
The Wikibook Practical Electronics has a page on the topic of: hole
sizes for through-hole parts
Wikimedia Commons has media related to Printed circuit boards.
PCB Fabrication Data - A Guide
The Gerber Format Specification