Hi Steve, Found this from our own Richard Stadem posted in Circuitnet, and should answer all your questions: To provide a flat pad, nickel is plated to the copper at a thickness of approximately 150 microinches (not 150 microns). Nickel oxidizes fairly quickly, so a very thin layer of gold (3 to 5 microinches) is subsequently plated over the nickel (not underneath as others have said) to prevent it from oxidizing. ENIG is preferred by some for that reason; the solderability remains excellent for years. The purpose of the nickel in ENIG is to provide a barrier between the copper pads and the gold. If the nickel is skipped and the gold is plated directly to the copper, a reaction will occur and over a very short time the copper will eat through the gold and can even appear on the surface as an "orange pad". You cannot solder to this pad without physically removing these oxides first. Chemical stripping can be done, but not without some collateral damage to other features, including the solder mask and the unprotected via walls. It is also very difficult to clean away 100% of the stripper, some always remains behind. During the soldering process, 100% of the 3 to 5u inches of gold on the top is immediately dissolved into the molten solder; no solder joint is formed with the gold. The underlying nickel is then exposed, and some of the nickel will dissolve into the molten solder, but no-where near all 150u inches of it. Your intermetallic layer is then made of the dissolved nickel into the solder alloy; you solder to the nickel barrier. The rate of dissolution of the nickel into molten tin/lead solder is 10 times slower than the rate of dissolution of copper into that same solder. At reflow temperatures, it takes a little bit longer to form a good IMF with nickel than it does with copper. Consider then, attempting to solder a PCB that has some pads with no nickel, some with, and some that may or may not have nickel under the gold. For those pads that meet the IPC 4552 standard, the gold will be immediately absorbed, and if the nickel is at least 100 u inches thick, no copper oxides will have formed, and the nickel should form a good IMF with the molten solder. For those pads that never had benefit of nickel, but are only exposed copper with a thin OSP coating that was probably applied several days after the problem was discovered and is subsequently oxidized to the level of a 1910 Lincoln penny, well, the chances of forming a good IMF between the solder and the copper is sort of like maybe, but probably not. When soldering, as others here have stated, some IMFs are going to form more than others, and while some IMF is usually enough, the fact is at least SOME of those pads that APPEAR to have plated over just fine and are actually skipped or nearly skipped and yet are covered with gold with some degree of nickel oxide barrier under the gold, who knows? You simply cannot solder to an oxide, once formed. Flux will not remove these types of oxide barriers effectively. With ENIG, a fabricator has to keep many, many process parameters under perfect control before, during, and after nickel plating, and even more so when doing the final gold plating. It is quite obvious that some or many things went wrong with this lot. So Tony Lentz and Jerry Karp gave you good advice; scrap the entire lot and tell the fabricator to replace them, and make sure the fabricator does not take the bad lot back and rework them and sell them to you later. Look for another fabricator who has some proven experience in ENIG plating. They have to run a very tight ship to plate ENIG properly (and any other finish as well, for that matter). A really good IPC-certified board shop can show you complete process control metrics, and the IPC has excellent standards for performing a PCB fabricator audit. [image: image]*Richard D. Stadem* <http://www.circuitnet.com/experts/panel_294.html> *Advanced Engineer/Scientist* *General Dynamics* Richard D. Stadem is an advanced engineer/scientist for General Dynamics and is also a consulting engineer for other companies. He has 38 years of engineering experience having worked for Honeywell, ADC, Pemstar (now Benchmark), Analog Technologies, and General Dynamics. On Mon, Jan 27, 2020 at 3:45 PM Dwight Mattix <[log in to unmask]> wrote: > Without the Ni barrier, the copper will diffuse through the gold rendering > it unsolderable. > > > -----Original Message----- > From: TechNet <[log in to unmask]> On Behalf Of Steve Smith > Sent: Monday, January 27, 2020 2:32 PM > To: [log in to unmask] > Subject: [EXT] [TN] Is Nickel really needed under the gold plating on > copper? > > Hi All, > > I was asked today if nickel is really needed under the gold for plating on > copper. I have understood it that the layer of nickel provides a mechanical > backing for the gold layer and that it was also needed for the soldering > process. Is this correct and is it the only reason it is used? > > > My regards, > > Steve Smith > Design Drafting Group Manager > Staco Energy Products > > O: 937.253.1191 x158 | F: 937.253.1723 > website< > http://www.stacoenergy.com/company/corporate-profile.html?utm_source=signature&utm_medium=email&utm_campaign=website> > | map< > http://www.stacoenergy.com/corporate-headquarters.html?utm_source=signature&utm_medium=email&utm_campaign=map> > | LinkedIn<https://www.linkedin.com/company/staco-energy?trk=ppro_cprof> > > > [cid:Healthcare-1908_840361ac-17f2-4e80-b79c-638c2e56eb87.png]< > http://www.stacoenergy.com/products-solutions/industries/healthcare.html?utm_source=signature&utm_medium=email&utm_campaign=healthcare > >< > http://www.stacoenergy.com/services/service-offerings.html?utm_source=signature&utm_medium=email&utm_campaign=Promo_Service-1903 > > > How are we doing? 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