Solder mask, solder stop mask or solder resist is a thin
lacquer
Lacquer is a type of hard and usually shiny coating or finish applied to materials such as wood or metal. It is most often made from resin extracted from trees and waxes and has been in use since antiquity.
Asian lacquerware, which may be ca ...
-like layer of polymer that is usually applied to the
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 ...
traces 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) for protection against
oxidation
Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a d ...
and to prevent
solder bridges from forming between closely spaced solder pads. A solder bridge is an unintended electrical connection between two conductors by means of a small blob of solder. PCBs use solder masks to prevent this from happening. Solder mask is not always used for hand soldered assemblies, but is essential for mass-produced boards that are soldered automatically using
reflow
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 subject ...
or
wave
In physics, mathematics, and related fields, a wave is a propagating dynamic disturbance (change from equilibrium) of one or more quantities. Waves can be periodic, in which case those quantities oscillate repeatedly about an equilibrium (res ...
soldering techniques. Once applied, openings must be made in the solder mask wherever components are soldered, which is accomplished using
photolithography
In integrated circuit manufacturing, photolithography or optical lithography is a general term used for techniques that use light to produce minutely patterned thin films of suitable materials over a substrate, such as a silicon wafer, to protect ...
.
Solder mask is traditionally green, but is also available in many other colors.
Solder mask comes in different media depending upon the demands of the application. The lowest-cost solder mask is
epoxy
Epoxy is the family of basic components or cured end products of epoxy resins. Epoxy resins, also known as polyepoxides, are a class of reactive prepolymers and polymers which contain epoxide groups. The epoxide functional group is also coll ...
liquid that is
silkscreened through the pattern onto the PCB. Other types are the liquid photoimageable solder mask (LPSM or LPI) inks and dry-film photoimageable solder mask (DFSM). LPSM can be silkscreened or sprayed on the PCB, exposed to the pattern and developed to provide openings in the pattern for parts to be soldered to the copper pads. DFSM is vacuum-
laminate
Lamination is the technique/process of manufacturing a material in multiple layers, so that the composite material achieves improved strength, stability, sound insulation, appearance, or other properties from the use of the differing materials ...
d on the PCB then exposed and developed. All three processes typically go through a thermal
cure
A cure is a substance or procedure that ends a medical condition, such as a medication, a surgical operation, a change in lifestyle or even a philosophical mindset that helps end a person's sufferings; or the state of being healed, or cured. The ...
of some type after the pattern is defined although LPI solder masks are also available in
ultraviolet
Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nanometer, nm (with a corresponding frequency around 30 Hertz, PHz) to 400 nm (750 Hertz, THz), shorter than that of visible light, but longer than ...
(UV) cure.
The solder stop layer on a flexible board is also called ''coverlay'' or ''coverfilm''.
In
electronic design automation
Electronic design automation (EDA), also referred to as electronic computer-aided design (ECAD), is a category of software tools for designing Electronics, electronic systems such as integrated circuits and printed circuit boards. The tools wo ...
, the solder mask is treated as part of the
layer stack
A printed circuit board (PCB; also printed wiring board or PWB) is a medium used in electrical and electronic engineering to connect electronic components to one another in a controlled manner. It takes the form of a laminated sandwich struc ...
of the printed circuit board, and is described in individual
Gerber files for the top and bottom side of the PCB like any other layer (such as the copper and
silk-screen layer
Screen printing is a printing technique where a mesh is used to transfer ink (or dye) onto a substrate, except in areas made impermeable to the ink by a blocking stencil. A blade or squeegee is moved across the screen to fill the open mesh ...
s).
Typical names for these layers include
tStop
/
bStop
aka
STC
/
STS
or
TSM
/
BSM
(
EAGLE
Eagle is the common name for many large birds of prey of the family Accipitridae. Eagles belong to several groups of genera, some of which are closely related. Most of the 68 species of eagle are from Eurasia and Africa. Outside this area, just ...
),
F.Mask
/
B.Mask
(
KiCad),
StopTop
/
StopBot
(
TARGET
Target may refer to:
Physical items
* Shooting target, used in marksmanship training and various shooting sports
** Bullseye (target), the goal one for which one aims in many of these sports
** Aiming point, in field artillery, fi ...
),
maskTop
/
maskBottom
(
Fritzing
Fritzing is an open-source initiative to develop amateur or hobby CAD software for the design of electronics hardware, intended to allow designers and artists to build more permanent circuits from prototypes. It was developed at the University o ...
),
SMT
/
SMB
(
OrCAD
OrCAD Systems Corporation was a software company that made OrCAD, a proprietary software tool suite used primarily for electronic design automation (EDA). The software is used mainly by electronic design engineers and electronic technicians to ...
),
MT.PHO
/
MB.PHO
(
PADS
Pads (also called leg guards) are a type of protective equipment used in a number of sports and serve to protect the legs from the impact of a hard ball, puck, or other object of play travelling at high speed which could otherwise cause injuries t ...
),
LSMVS
/
LSMRS
(
WEdirekt)
or
GTS
/
GBS
(Gerber and many others
).
Notes
References
Further reading
*
Printed circuit board manufacturing
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