Pros: Less expensive than gold, Gold embrittles solder.|
Cons: Gold is a LESS corrosive surface than any solder. If wire bondability is important, solder is not wire bondable. Why don't you look at electroless Ni, immersion Pd as an
alternative. The IP is very thin so cost is low and it's both solderable and
Process Solutions Consulting Inc.
Lee Levine has been a Process Engineer and Metallurgist in the semiconductor industry for 30 years. He now operates his own company Process Solutions Consulting Inc where he consults on process issues and provides SEM/EDS and metallography services.
The Gold is a better finish for the corrosive environment if it
is clean going into the field. HASL will typically use a very corrosive
flux to prepare the surface and if this is a lead free HASL or leaded it does
not matter, both are susceptible to corrosion. These must be very clean
going into the fielded environment or just the residue from the HASL process
can set up corrosion cells. The plating process for the gold finish is not as difficult
to clean and the residues are typically very low even with RO water
President/Senior Technical Consultant
Mr. Munson, President and Founder of Foresite, has extensive electronics industry experience applying Ion Chromatography analytical techniques to a wide spectrum of manufacturing applications.
nature ENIG is better than HASL with corrosive environment. Be careful upon
migration to HASL if you are using BGA, Fine pitch IC [pitch<20mil] because
of co-planarity is not the best as in ENIG. If really corrosion is concern in
present Board ENIG preference to be given for conformal coating Acrylic type -
MIL grade approved to minimize corrosion as well coating should meet minimum
thickness requirement per MIL std without changing finish type.
Supplier Quality Leader
Subrat has 10 year of extensive experience in PCB assembly process optimizing for quality, process includes screen printing, wave, reflow. He has a copyright in stencil design published in Apex Expo2010 at Las Vegas US.
If electronics are being
used in a corrosive chemical environment it would be advised to use a
polyurethane conformal coating which would protect both HASL and ENIG finishes
Generally a material that meets G3 noxious gas
testing would be advised.
Chris Palin is currently managing European sales and support for HumiSeal Conformal Coatings. His expertise is in test & reliability, solder technology, power die attach and conformal coating.
There is really no one-size-fits-all answer to this question.
The answer for your application really depends on the following factors and
probably other factors as well:|
In general, ENIG finishes are relatively robust to corrosive
atmospheres. HASL finish is also quite robust, though exposed solder surfaces
can corrode and produce ionic species. The advantage of HASL is that the PWB
finish has the same corrosion behavior as the solder joints, so it doesn't have
to be evaluated separately.
There is risk of exposed copper with both HASL and ENIG
finishes, mainly on the edges of traces and lands. In my experience, it happens
more with HASL than it does with ENIG. Exposed copper can corrode easily and
produce highly ionic salts, some of which are water soluble (copper sulfate,
for instance). These salts represent a high reliability risk.
finishes such as immersion silver or OSP are much less resistant to corrosion
than HASL or ENIG. I would not recommend either of them in a corrosive
- The types and concentrations of corrosive species in the
atmosphere in your application.
- The level of venting present in your product. This could be
anything from well-sealed to forced-air fan cooled.
- The electrical nature of the product, including voltage levels,
spacings, circuit impedances, etc.
- Whether or not the assemblies are conformal coated or potted,
and if so with what material and process.
Fritz's career in electronics manufacturing has included diverse engineering roles including PWB fabrication, thick film print & fire, SMT and wave/selective solder process engineering, and electronics materials development and marketing. Fritz's educational background is in mechanical engineering with an emphasis on materials science. Design of Experiments (DoE) techniques have been an area of independent study. Fritz has published over a dozen papers at various industry conferences.
you are leaving exposed pads or test points that will be susceptible to
atmospheric attack then there have been a number of papers published that
indicate HASL's superiority over the majority of surface finishes. However HASL
comes at it's own price re placement issues and it is one of the dirtier (ionic and bi-polar organic contaminant) finishes. If all test points/pads are
soldered then there is no advantage to struggling with HASL as the surface
finish. Depending on the atmosphere in which the end product operates may make
ENIG a suitable finish - you would have to provide more information re S, SO2,
Cl levels etc as well as temperature/humidity levels expected to be seen and if
there is the possibility of a condensing atmosphere being in contact with the
S T and S Testing and Analysis
Gerald O'Brien is Chairman of ANSI J-STD 003, and Co Chairman of IPC 4-14 Surface Finish Plating Committee. He is a key member of ANSI J-STD 002 and 311 G Committees Expert in Surface finish, Solderability issues and Failure analysis in the PWA, PWB and component fields.
This is an interesting
question from the perspective of utilizing the finish solderability coating on
raw boards for a protective coating in its functional life.
The coating applied to raw
boards is to guarantee and preserve some degree of solderability during its
storage and assembly life cycle. The major difference between the two coating
be it either HASL or ENIG is related to the types of components being assembled
on the boards and their requirements for flatness of the pads. The topography
of the HASL boards can at times impact the reliability of BGA component as the
pads are different thicknesses and the solderability can be problematic,
whereas the ENIG boards are flatter, which would results in more consistent
solder joints across the components. Although there are other benefits to each
type, these are the two of the biggest concerns, while the next would be the
change from HASL to ENIG to create a lead-free product.
ENIG boards can be
problematic from the perspective of Gold thickness and Gold porosity, where in
fact the solder joint is made through an interaction between the tin in the
solder and the nickel barrier on the board. One problem that has been
experienced through the years has been the black pad issue which is related to
gold plated boards. This issue is a result of the plating process and can be a
major solderability issue with components whose solder joints are beneath the
component such as BGA components. Proper qualification of the board fabrication
shops and constant monitoring of those shops is a must to make sure this
problem does not exists or rear its ugly head.
As for using these
solderable coatings for protective measures, these coatings must be fully
evaluated from a product reliability perspective which is different than their
solderability requirements. To prevent interaction problems with various
environments in the field many users apply a conformal coating to the assembly
prior to final test and assembly into their operational product. This conformal
coat does provide some measure of protective coating to the various
environmental excursions the product may be subjected to during its operational
As to which coating I would
recommend, this is most difficult as there are the failure mechanisms of the
two coatings to consider which would occur based upon your requirements.
Corrosive environments would impact the tin from solder coating and if the gold
was porous the corrosive vapors would impact the nickel barrier coating. In
both cases it would also impact the laminate material which is where the
biggest issue is from my perspective and that change would be in the dielectric
constant of the laminate material which will impact the functional operation of
the product. This is why any product which is going to be subjected to
corrosive environment should be conformal coated and sealed to protect it from
the operational environment. Hope
this is useful.
Vice President, Technical Director
At EPTAC Corporation, Mr. Lambert oversees content of course offerings, IPC Certification programs and provides customers with expert consultation in electronics manufacturing, including RoHS/WEEE and lead free issues. Leo is also the IPC General Chairman for the Assembly/Joining Process Committee.
ENIG is a good
candidate for High Phosphoric Corrosion resistance.
This is the plating
of choice for Printers, TeleCom and others in the industry. Care should
be taken, to specify the Gold and Anvil structure, but this is industry
preferred Solder Finish.
HASL could offer an
inert option, as a Pb Solder type, but I wouldn't believe this to be preferred
Capital Equipment Operations Manager
Specialty Coating Systems
Rodney is currently Operations manager at SCS coatings, Global Leader in Parylene and Liquid Coating equipment. Rodney applies his BS in Computer Integrated Manufacturing from Purdue University, along with 20+ years of Electronic manufacturing and Equipment Assembly, to direct the Equipment business at SCS Coatings. "We provide unique, value added coating equipment solutions for our customers". Including conformal, spin and Parylene coating expertise.
Immersion gold is not
intended as a final finish. Rather, it's purpose is to preserve the
solderability of the metal it covers, and it's application is limited to the
assembly process. Volumes are written about the shelf life of immersion
coatings -- including gold -- but there is no established
performance measure for immersion gold as a final finish. As such, most PCB
designs have via pads covered in solder mask, leaving only the solderable lands
exposed. And because these lands variously receive assembly solder, my answer
Robert "Bob" Lazzara
Circuit Connect, Inc.
Bob has been in PCB design and fabrication since 1976. He has held elected positions with the SMTA, is a member of the MSD Council, has served as a committee member for various IPC standards and is a Certified IPC Trainer.
HASL will produce a much thicker deposit of solder to
wet to BUT it can leave traces of Hydrobromic Acid and Hydrochloric acid plus
lots of High Boiling Hygroscopic solvents to cause Corrosion and SIR issues
anyway, so be very wary. I would use a good Chemical resistant conformal
coating then stick with Nickel gold finish. Most fluxes can be coated over now
a days so don't clean just leave in place as cleaning itself can cause issue's
with undercured solder resist absorbing conductive cleaners then not rinsing
Technical Sales Manager
BLT Circuit Services Ltd
Greg York has twenty two years of service in Electronics industry. York has installed over 350 Lead Free Lines in Europe with Solder and flux systems as well as Technical Support on SMT lines and trouble shooting.
If all the areas are soldered, then it should
not matter. Both immersion gold and HASL should perform equally
well. If there are locations that are not soldered, then the immersion
gold layer is likely too thin to prevent the underlying metals from
corroding. So if areas are not soldered, HASL would be better.
Renee has been with Trace and an IPC member for 16 years. She has managed all military and commercial PB qualification and conformance testing and training, as well as product qualification and testing in the areas of solder pastes, fluxes, solder masks, and conformal coat. She is the chairman of the IPC Testing and the IPC-J-STD-004 Flux Specification Committees and the Vice Chairman of the Assembly and Joining Committee. She has published more than a dozen papers and presented at numerous electronics conferences.
Do you recommend use of HASL vs. immersion
gold for our application? Yes.
Would you recommend another type of finish? Sn/Pb plate and fuse.
SME - PWB Technologies
Mahendra Gandhi has been working in interconnect industry since 1972.
usually recommend ENIG as a plating over HASL for those customers who have
applications for printed circuit board assemblies that are or can be exposed to
corrosive environments not so much for corrosion resistance but to help advance
the cleanliness of the finished product specifically to prevent flux
reactivation and possible dendritic growth which can thrive in such situations.
By the nature of the process, ENIG as a plating does not have residual flux
residues but HASL does (in some cases excessive) and therefore the cleanliness
of the board fabrication as received will depend upon the effectiveness of the
cleaning process of the board fabrication supplier. As such a HASL plated board
will automatically start out with elevated levels of anionic and cationic
contamination (which will only be added to by the assembly process) so I would
definitely recommend an ENIG plated board fabrication to be used in corrosive
environments for this reason.
We do ionic chromatography testing internally on
blank board fabrications and the finished product where cleanliness is
concerned for high reliability applications to ensure that they meet minimal
requirements prior to acceptance and repeatedly find that assemblies starting
off with ENIG plating are in general cleaner than those assemblies that use
HASL plated board fabrications.
Sales & Marketing Manager
Technical Manufacturing Corp.
David has been active in all areas of the contract electronics manufacturing industry for over fifteen years. He is currently in charge of all Sales and Marketing related activities for Technical Manufacturing Corporation.
An ENIG finished circuit board would have no exposed copper whatsoever. HASL has, however, at the undercut. From this perspective, ENIG is a better choice; a little bit more expensive, though.
Alan Lee, Finenet Electronic Circuit Ltd., Hong Kong, PRC.