Adding OSP to Pads that are Missing ENIG Plating Process
A fabricator recently notified us that during the ENIG plating process, several pads had been “skipped” and missed on a number of boards. The fabricator would like to add OSP to the pads that are missing the ENIG. Is this acceptable? Board Talk
Board Talk is presented by Phil Zarrow and Jim Hall of ITM Consulting.
Process Troubleshooting, Failure Analysis, Process Audits, Process Set-up CEM Selection/Qualification, SMT Training/Seminars, Legal Disputes
Phil Zarrow
With over 50 years experience in PCB assembly, Phil is one of the leading experts in SMT process failure analysis.
He has vast experience in SMT equipment, materials and processes.
Jim Hall
A Lean Six-Sigma Master Blackbelt, Jim has a wealth of knowledge in soldering, thermal technology, equipment and process basics.
He is a pioneer in the science of reflow.
Transcript
Phil
And welcome to Board Talk with Phil Zarrow and Jim Hall, The Assembly Brothers, Pick and Place. We are here to talk about assembly, processes, materials, equipment, methodologies, and all of those fun things that while our day away. Jim, what is today’s question?
Jim
It comes from S.N. A fabricator recently notified us that during the ENIG plating process, several pads had been "skipped" and missed on a number of boards. The fabricator would like to add OSP to the pads that are missing the ENIG. Our fabrication drawing clearly specifies ENIG, so I think the boards should be either replated with ENIG or scrapped at the fabricator’s expense.
Phil
Hey Jim, is this a gag question?
Jim
Phil, you’re my customer. I made some mistake with your product so I put some band-aids on it and good luck.
Phil
It's probably time to find another board fabricator. I don’t even know where to begin with this. Starting with the fact that your drawing clearly specifies ENIG. The process is clearly well out of control. It is time to find another fabricator. But to answer your specific question, no way. Jim, you want to add to that?
Jim
Phil, play a mind game with this thing. He says skipped. Well, what was skipped? Was the gold skipped? If that is the answer, then I am putting OSP over nickel. If the nickel and the gold were skipped, then you could argue that it is OSP over copper. That is the standard process. What else is going wrong with the plating?
Phil
Yeah, that is what you have noted.
Jim
Think about black pad. One of the things we know is that pads come to us with black pad; they look good. They have gold on them, but when we go to solder them, they get a weak joint. If we have skips on the gold, then what is going on under the other gold that is there? Are we just looking at a massive potential black pad problem? I don’t know. That is the question.
You shouldn’t have to take that variability into your process. I want to step back and say, as an assembler, the PCB is an incoming material; it should be right. It should be to spec. We have enough problems assembling boards and getting good quality and everything else without dealing with variable, not-to-spec incoming materials.
Phil
This is what you have seen, and that is what you have seen on this batch of boards. What might have slipped past you? The bottom line with this fabricator is run away, run away. You have to be doing better than that. We will see if anyone comes to the defense of the fabricator, but that is pathetic. No, you don’t put OSP over that.
You have been listening to Board Talk with Jim Hall and Phil Zarrow, The Assembly Brothers. However your surface finish is, whatever you try to solder to it, just don’t solder like my brother.
Jim
And don’t solder like my brother.
Comments
Basically, the board shop is clearly unreliable, and the product they produced will certainly be unreliable, no matter how much anyone may talk and cajole to the contrary, they are unreliable. So, it is your choice, use unreliable product or not. Because they 'missed' you have no obligation to pay for the scrap heap they created. Find another shop that is trust-worthy (I can give you a short list of shops that are not to be trusted, off-line, if you wish), there are many good shops, who take pride in making fine boards.
Jaye Waas, Renkus-Heinz
This may be another question for another Board Talk entry, but I do not specify selective/pattern place versus covering all copper surfaces with ENIG. My expectation is, in absence of a note allowing selective plating, I will get full coverage of ENIG. Is that a realistic expectation?
Stephen Wint, Astek Corporation
Love your site and the questions you get! My comments relate to board testing: So time is running out, customers are waiting and you have no choice but accept a single lot of boards that missed the ENIG process. Maybe the mask was wrong and the pads have bare copper so putting OSP is the next logical solution to prevent the copper from oxidizing. But because of the OSP dip process, all of the pads both the ENIG and copper and the rest of the board have OSP on it. While that thin organic protection layer is supposed to be easy to probe through, but depending on how many reflows the board is subjected to and the oven atmosphere, that impossibly thin layer of OSP is now much harder to penetrate for board testing.
If you've already got the bed of nails fixture set up to use low force probes with flat and domed tips, you are going to fail ICT, this tip/spring force configuration will not make a reliable contact through OSP. If you are using sharp chisel and "Razor" tip style probes, the chances of passing board test will improve but you may find that you'll need both sharp chisels and higher springs forces to be successful. Back when OSP was the new solution for reduced board manufacturing cost, fabricators were routinely replacing solder pads with OSP, Agilent did a big study and published a white paper basically telling you that if you want reliable tests you'll need to reflow solder onto the OSP copper test points.
For the fabricator that missed the ENIG test points and a board deadline approaching, making a stencil that puts solder on the OSP/Copper pads will help as the solder flux basically eats away the OSP during the soldering process and you'll be contacting an easy to probe solder pad. However that does not help the ENIG pads because they will still have OSP. If you are not performing any bare-board, in-circuit, loaded-board or functional testing then the biggest issue is that OSP will cover all features of the board and this may be undesirable.
Matt Parker, QA Technology Co. Inc.
I agree with Phil and Jim, time to find another FAB house, but I think we need to check the Gerber files to make layer information is correct to have all locations plated.
