Electroless nickel immersion gold - Page 1
Forum section: electronics / general

author: bostonman
author_rank: Super Contributor
timestamp: September 19, 2022, 02:23:04 am
content: Is Electroless nickel immersion gold on PCBs real gold, and, if so, how much?I came across a board that looked like it has a gold finish, and, after research, found this is Electroless nickel immersion gold (or ENIG), so I began wondering just how much gold is on this board (or if it's even gold that can be scrapped off and sold).

author: ataradov
author_rank: Super Contributor
timestamp: September 19, 2022, 03:03:55 am
content: If you only have one PCB, then it is not worth it. It only starts to make sense on a semi-industrial scale. ENIG layer is typically fractions of a micrometer. Just recovering the copper would be way more profitable.There are a ton of forums with people that deal with recycling. Just search for "ENIG recycling" and you will find videos and forum posts.There is no way to "scrape it off", typically you just grind the PCBs and use mechanical and chemical extraction. All of the chemistry involved is pretty nasty and is not something you can do at home.

author: bostonman
author_rank: Super Contributor
timestamp: September 19, 2022, 03:39:21 am
content: Thanks.Hopefully I didn't imply I was thinking I could retire off the gold on this board, but was curious whether it was real gold or more minerals mixed with a minuscule amount of gold.I remember reading (or seeing on TV) that some people hang outside jewelry stores or some place in New York sifting through the sidewalk cracks looking for gold that came off employees' shoes as they exited the facility.On a side note, and maybe my memory is failing me, but at an old job we used gold plated connectors. It was determined that "gold embrittlement" was causing issues with the solder joints. After doing a quick Google search, it seems if the gold exceeds 3% of the total weight of the solder, the solder joint can become weak.If this is true, why would anyone use ENIG on a board?

author: ataradov
author_rank: Super Contributor
timestamp: September 19, 2022, 03:45:01 am
content: Quote from: bostonman on September 19, 2022, 03:39:21 amWell, you can recover meaningful amount of palladium from road dirt along busy roads. It comes out of catalytic converters.Quote from: bostonman on September 19, 2022, 03:39:21 amIt is a compromise, and for most applications it is not a problem. ENIG is flat and easily solderable. But in some cases you see that critical components are left with bare copper. One example is iPhone PCBs, where main BGA chips have plain copper and the rest of the components use ENIG.

author: bostonman
author_rank: Super Contributor
timestamp: September 19, 2022, 03:54:31 am
content: Oh wow, bare copper?I assume they have to be stored in some protective bag to avoid them oxidizing.Any PCB with bare copper wouldn't be bare after the components are mounted, correct?If I work on something (like my old C64 units) and find the masking has come off leaving copper exposed, I try applying solder to it to avoid any oxidation. Although, in many cases it's impossible to fix an entire PCB this way and I end up giving up.

author: ataradov
author_rank: Super Contributor
timestamp: September 19, 2022, 04:06:46 am
content: Quote from: bostonman on September 19, 2022, 03:54:31 amYes, and realistically only Apple with its scale can pull this off. Everyone else just uses ENIG and deals with the consequences.Solder paste and BGA balls formulations also affect things. Manufacturing things at scale and reliably is not easy.Quote from: bostonman on September 19, 2022, 03:54:31 amCorrect. A common (and cheaper) alternative to ENIG is HASL (hot air solder leveling), which is exactly that - cover all exposed copper parts with solder instead of gold. But HASL leaves relatively uneven surface, so it is not suitable for small components.Quote from: bostonman on September 19, 2022, 03:54:31 amIt is a good idea to do as much as you can, but in the end it is not such a huge problem to lose sleep over. Alternative may be UV curable solder mask liquid. It is readily available and lets you work on the cover before you fix it with UV.

author: bostonman
author_rank: Super Contributor
timestamp: September 19, 2022, 11:29:21 pm
content: QuoteI was unaware so many finish options exist for PCBs. I thought all basic PCBs are dipped in solder or whatever. Is this different than HASL? I'm sure I can find a YouTube video on professional PCB building, but, from my understanding: it's a layer of FR4, copper is poured onto this, a machine etches off all unused areas, another layer of FR4 is glued (?) on top, copper pour, etching, etc... until all the layers are built. Then holes are drilled for vias and through-hole components, barrels are inserted, the board is dipped in solder, the mask is poured on, and then silkscreening.Are the middle layers left as copper or are they too dipped in something based on the customer request?QuoteI assume this needs to be applied carefully so it doesn't end up covering components on an existing populated board?I'm uncertain of PCB evolution, but, from what I can tell, the C64 board(s) I've see can have the green mask pulling off like an onion because I see what looks like bubbles. Maybe it's due to age, maybe the technology back then, or maybe Commodore went cheap with their mask request.

author: ataradov
author_rank: Super Contributor
timestamp: September 19, 2022, 11:41:51 pm
content: Quote from: bostonman on September 19, 2022, 11:29:21 pmThis is the first step of HASL. The second part is "scraping" the board while solder is still molten with air blades (like in toilet hand dryers, but way stronger). It is a pretty violent process, but without this step you will have a lot of solder stuck to the board making it unusable.Quote from: bostonman on September 19, 2022, 11:29:21 pmThere is no pouring, copper sheet is laminated to the substrate. PCB fabs get pre-made laminates. Multi-layer PCBs are build from multiple thin laminated boards that are laminated together after etching.Quote from: bostonman on September 19, 2022, 11:29:21 pmThey are just plain copper, there is no need to do anything special to them.Quote from: bostonman on September 19, 2022, 11:29:21 pmWell, you need to cover just the exposed copper. It is a thick liquid (like nail polish), so it is not that hard to apply in a very targeted way.Quote from: bostonman on September 19, 2022, 11:29:21 pmIt depends on what you see exactly. There are two tings that are often confused. If it just peels off, then it is just a bad solder mask. This is somewhat typical for old stuff.But another thing you may see is that solder mask is adhered well, but has uneven surface and looks like it has bubbles. This happens because PBC tracks under the mask have solder on them, and unlike with HASL, that solder is not removed, so it clumps up on wider traces and polygons. This is also very common in old PCBs.

author: bostonman
author_rank: Super Contributor
timestamp: September 19, 2022, 11:52:46 pm
content: QuoteMaybe I'm wrong then. I thought a co-worker at an old job who did PCB said they specify the copper thickness based on "pouring".I think our old drawings would specify "copper pour thickness 0.062' " unless I'm confusing things.

author: ataradov
author_rank: Super Contributor
timestamp: September 20, 2022, 12:01:50 am
content: You do specify copper thickness, but I'm not sure where the "pour" comes from. As far as I know it has never been made by pouring. I'm pretty sure it is just rolled into sheets and then glued to the fiberglass.Copper filled areas (as opposed to the tracks) on the PCB are often called "pours", but their thickness is the same as of traces. They are called that because your action in the PCB editor is similar to pour fill in a graphics editor, not because it has anything to do with the PCB manufacturing process.

author: bostonman
author_rank: Super Contributor
timestamp: September 20, 2022, 12:44:48 am
content: You could be correct about me mistaking "pour" for the copper pour when laying out the PCB.I did find a PCB drawing that has the following:Board material: Epoxy-Glass (FR4)Board Design Type: SMT1Construction per 926.410: A59F (this could be a company standard)Copper weight by layer: outer layer copper is 0.5oz/SQ FT, inner layer copper is 1oz/SQ FTPlating finish per 926.410: 17 (this could be a company standard)The copper weight could be something I came across at my old job, and associated it with, or incorrectly remember, what was told me about the copper being "poured on".

author: ataradov
author_rank: Super Contributor
timestamp: September 20, 2022, 01:08:59 am
content: Copper thickness is generally specified by weight of a square foot. 0.5oz copper is slightly unusual, especially on outer layers.For signals it generally does not matter, and different vendors would have different capabilities. But if you look at typical cheap vendors, they use 1 oz on outside and 0.5 oz on the inside layers. Outside layers can be changed to 2 oz for extra cost, but inner layers are typically limited to 0.5 oz.You also need to keep in mind that part of the outside layers comes from plating. The material itself is usually 0.5 oz. But in order to get plated though holes, you have to plate the whole board, which also grows the copper layer on top of the base 0.5 oz copper.And you don't want to over-specify parameters that you don't actually need, since you will be limiting your options in manufacturers and possibly increasing the price quite a bit. It is always better to see if a standard stackup works for your design. Most designs are fine with that.Just for an illustration, here is a very clean typical stack up for a 4 layer board:https://docs.oshpark.com/services/four-layer/

author: bostonman
author_rank: Super Contributor
timestamp: September 20, 2022, 02:37:31 am
content: I've only done a few boards and never dove into any specifications, but it makes sense the more you demand, the higher the cost.Over the years I've seen various boards. One board if I remember correctly was thin and flexible (for high frequency), and recently a board with ten layers with gold on the outside (which is what made me ask the initial question in this thread).Doubt I'll ever need to remask a board, and the C64 boards weren't really worth it, but good to know it can be done using a UV lamp.