Introducing ASIG Autocatalytic Silver Immersion Gold

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Introducing ASIG Autocatalytic Silver
Immersion Gold
Polymer Kompositer AB is proud to introduce the
worlds first really cost effective multi purpose
final finishing for PCBs ASIG -
Autocatalytic Silver Immersion Gold
A revolution in PCB surface finishing ASIG
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Why ASIG?
ASIG has been developed as a high-quality
replacement for ENIG. However, since the process
is more cost effective than ENIG it may replace
other final finishes as well that demands the
very best in solderability, bondability, shelf
life and reliability. As such, ASIG has the
best price to performance ratio in the Industry.
A revolution in PCB surface finishing ASIG
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Why does ASIG excel?
The secret behind the superior performance and
low cost of the ASIG process lies in the patent
applied for technology and processing sequence.
The ASIG process consists of three steps
A revolution in PCB surface finishing ASIG
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Strep 1 ASIG PreDip
The ASIG PreDip is a very mild immersion silver
plating process. It therefore deposits a very
dense, however very thin silverfilm (lt0,1µm).
Thickness buildup is not done in the immersion
reaction since this would cause a too porous
silverfilm. Providing a dense silver-film, the
target thickness of 0,7-1µm is reached in the
unique AUTOCATALYTIC reaction in step 2 - ASIG
Silver.
ASIG PreDip bath
Ag
Ag
Cu2
Ag
Ag
Ag
Cu2
Cu2
Ag
Ag
Ag
Cu2
Cu2
Ag
ASIG PreDip
Cu
Cu
Cu
Cu
Cu
Ag
Ag
Ag
Ag
Ag
Cu
Cu
Cu
Cu
Cu
Cu
Cu
Cu
Cu
Cu
PCB Copper getting covered with a thin but
extremely dense silverfilm
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Step 2 ASIG Silver
The ASIG Silver is an autocatalytic silver
plating bath. The autocatalytic silver-deposition
is maintained with the aid from a reducing
agent. The ASIG Silver creates a pore-free and
very thick silverfilm that effectively blocks any
diffusion of copper through the silver-film
during multiple solder reflows or during ageing.
ASIG Silver bath
Ag
Ag
Reducing Agent
Reducing Agent
e-
e-
Ag
e-
e-
Ag
Ag
Ag
ASIG Silver
Ag
Ag
Ag
Ag
Cu
Cu
Cu
Cu
Cu
Ag
Ag
Ag
Ag
Ag
Cu
Cu
Cu
Cu
Cu
Cu
Cu
Cu
Cu
Cu
PCB after ASIG PreDip and building up silver
thickness (0,7-1µm) in ASIG Silver
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Step 3 ASIG Gold
Due to the autocatalytic silver deposition in
ASIG Silver, the silver film is thick enough for
succeeding immersion deposition of gold. Due to
the small potential difference between gold and
silver and silvers inertness for corrosion it is
possible to deposit a very thin gold layer on top
of the silver-film. The result is a significant
cost-cut compared with the ENIG process.
ASIG Gold bath
Ag
Au3
Ag
Ag
Au3
Au3
Ag
Au3
Ag
Au3
Ag
Ag
Ag
Ag
Ag
Au
Au
Au
Au
Au
ASIG Gold
Ag
Ag
Ag
Ag
Ag
Cu
Cu
Cu
Cu
Cu
Ag
Ag
Ag
Ag
Ag
Cu
Cu
Cu
Cu
Cu
Cu
Cu
Cu
Cu
Cu
PCB after ASIG Silver depositing a very thin
gold layer (lt0,03µm) with ASIG Gold.
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ASIG A high-quality replacement for ENIG
The ASIG final finish was originally developed as
a replacement for the ENIG process, which in
recent studies made by e.g. Nokia has revealed
serious reliability problems with e.g. blackpads,
dry lake phenomenon etc. The reason for the
quality problems with ENIG can be found in the
characteristics of Ni as a metal. The following
slides is an overview of quality problems
associated with the ENIG finish. For a more
thorough explanation of why the ENIG finish is
more prone to brittle solder-joints than other
surface finishes, an excellent study has been
conducted by Dr. Per-Erik Tegehall at IVF (A
leading Swedish research institute).
Autocatalytic Silver Immersion Gold ASIG
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ASIG A high-quality replacement for ENIG

• Ni is a hard and during soldering even more
  brittle intermetallic layers are formed. When
  used under for instance BGAs, the Ni causes
  brittle solder-joints when the PCBs are stressed.

Autocatalytic Silver Immersion Gold ASIG
BGA capsule during drop test.
Fracture in the brittle IMC in a BGA solder-joint.
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ASIG A high quality replacement for ENIG

• Ni is prone to oxidize. Most of the problems
  associated with the ENIG final finish have their
  origin in the formation of hyper-corrosive nickel
  resulting in black-pads.

Autocatalytic Silver Immersion Gold ASIG
Black-pad also referred to as dry-lake
phenomenon
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ASIG A high quality replacement for ENIG

• The ASIG final finish solves the quality problems
  inherent in the ENIG finish because the nickel is
  not there anymore in the ASIG process nickel is
  replaced by a very dense silver-film. This is a
  major advantage as silver has quite opposite
  characteristics than nickel
• Silver is a ductile (soft) metal which during the
  solder process is dissolved in the lead. Hence,
  the solder joint is formed against underlying
  copper instead of soldering against the brittle
  Ni as on an ENIG Surface.
• Silver reacts much slower with oxygen than does
  nickel. Hence, silver does not corrode and
  therefore solves the issue of black-pads.

Autocatalytic Silver Immersion Gold ASIG
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ASIG A cost effective alternative to ENIG

• Who would have thought that something made out of
  pure silver and gold could be cheap?
• Compared to the ENIG-process, ASIG does not only
  increase quality it also reduces processing
  cost. These are the reasons why
• Reduced gold consumption
• Complete elimination of Pd
• Easier and less energy intensive processing

Autocatalytic Silver Immersion Gold ASIG
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ASIG Reduced gold consumption
In the ASIG process, the gold layer is extremely
thin less than 0,03µm. This reduces cost
considerably compared to the thickness required
in the ENIG process. What makes it possible to
reduce gold thickness is the lower potential
difference between silver and gold vs. the
potential difference between nickel and gold. A
much thinner gold-layer is enough for protecting
the silver to form oxides.
Autocatalytic Silver Immersion Gold ASIG
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ASIG Elimination of Palladium
The ASIG process does not utilize a Pd activation
system as the ASIG PreDip starts depositing
silver directly onto the copper. Palladium
activation is therefore superfluous and the
costly metal can be avoided.
Autocatalytic Silver Immersion Gold ASIG
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ASIG Easier and low energy consumption
processing
Comparing the processing sequence suggest that
ASIG is a more straight forward process than
ENIG. In addition, lower processing
temperatures Used in the ASIG process results in
less energy consumption and higher acceptance for
solder masks.
Autocatalytic Silver Immersion Gold ASIG
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ASIG Easier processing
ASIG
Autocatalytic Silver Immersion Gold ASIG
60C
Pd-activation and its rinse Eliminated in ASIG
Gold thickness lt0,03µm
Gold thickness 0,05-0,1µm
ENIG
90C
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ASIG A summary of benefits (1)

• The Industrys best-ever seen bondability with
  both gold and aluminium wire
• Excellent shelf life (estimated to three years)
• Excellent solderability that remains unaffected
  after
• multiple reflows due to thick and dense silver
  deposits that blocks diffusion of copper.
• Compared to ENIG the cost is reduced by easier
• and a less energy consuming processing.

Autocatalytic Silver Immersion Gold ASIG
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ASIG A summary of benefits (2)

• Cost is further reduced by eliminating the costly
  palladium activation as well as a significant
  decreased usage of gold.
• ASIG does not suffer from quality problems such
  as black pads or other inferior quality
  phenomenons associated with the ENIG process.
• Wear resistance anticipated to be satisfactory
  for use under spring loaded connectors and
  press-fit connectors.
• Superior wetting/solderability

Autocatalytic Silver Immersion Gold ASIG
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Contact Polymer Kompositer AB
For further questions, please do not hesitate to
contact us.
Jens Andersson, Managing Director 46 176
75850 jens_at_polykomp.se
Autocatalytic Silver Immersion Gold ASIG