Electroless nickel immersion gold (ENIG or ENi/IAu), also known as immersion gold (Au), chemical Ni/Au or soft gold, is a metal plating process used in the manufacture of
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 ...
s (PCBs), to avoid oxidation and improve the solderability of copper contacts and
plated through-holes. It consists of an
electroless nickel plating, covered with a thin layer of
gold
Gold is a chemical element with the symbol Au (from la, aurum) and atomic number 79. This makes it one of the higher atomic number elements that occur naturally. It is a bright, slightly orange-yellow, dense, soft, malleable, and ductile met ...
, which protects the nickel from oxidation. The gold is typically applied by quick immersion in a solution containing gold salts. Some of the nickel is oxidized to while the gold is reduced to metallic state. A variant of this process adds a thin layer of
electroless palladium over the nickel, a process known by the acronym ENEPIG.
ENIG can be applied before or after the
solder mask, also known as overall or selective chemical Ni/Au, respectively. The latter type is more common and significantly cheaper as less gold is needed to cover only the
solder pads.
Advantages and disadvantages
ENIG and ENEPIG are meant to replace the more conventional coatings of
solder, such as
hot air solder leveling {{unreferenced, date=November 2012
HASL or HAL (for hot air (solder) leveling) is a type of finish used on printed circuit boards (PCBs).
The PCB is typically dipped into a bath of molten solder so that all exposed copper surfaces are covered by so ...
(HASL/HAL). While more expensive and require more processing steps, they have several advantages, including excellent surface planarity (important for
ball grid array component mounting), good oxidation resistance, and suitability for movable contacts such as
membrane switch
A membrane switch is a custom switch assembly that can open or close the conducting path in an electrical circuit and requires at least one contact made of or attached to a flexible substrate. Its assembly differs from traditional mechanical switc ...
es and plug-in
connectors.
Early ENIG processes had poor adhesion to copper and lower solderability than HASL. In addition, a non-conductive layer containing nickel and phosphorus, known as "black pad", could form over the coating due to sulfur-containing compounds from the solder mask leaching into the plating bath.
Standards
The quality and other aspects of ENIG coatings for PCBs are covered by
IPC
IPC may refer to:
Computing
* Infrastructure protection centre or information security operations center
* Instructions per cycle or instructions per clock, an aspect of central-processing performance
* Inter-process communication, the sharin ...
Standard 4552A,
while IPC standard 7095D, about ball array connectors, covers some ENIG problems and their remediation.
See also
*
Immersion silver plating
Immersion silver plating (or IAg plating) is a surface plating process that creates a thin layer of silver over copper objects. It consists in dipping the object briefly into a solution containing silver ions.
Immersion silver plating is used by ...
(IAg)
*
Immersion tin plating
Immersion may refer to:
The arts
* "Immersion", a 2012 story by Aliette de Bodard
* ''Immersion'', a French comic book series by Léo Quievreux
* ''Immersion'' (album), the third album by Australian group Pendulum
* ''Immersion'' (film), a 2021 ...
(ISn)
*
Organic solderability preservative
Organic solderability preservative or OSP is a method for coating of printed circuit boards. It uses a water-based organic compound that selectively bonds to copper and protects the copper until soldering.
The compounds typically used are from the ...
(OSP)
*
Reflow soldering
*
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 ...
References
Printed circuit board manufacturing
Metal plating
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