Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Black Pad

razor

#24278

Black Pad | 24 April, 2003

Known: During PCB maufacting nickel alloys are used for corrosion resistance during gold immersion process. A nickel alloy with a high phosphorus concentration will cause a weak connection interface. Question: Is the concentration of phosphorus in nickel alloys a key process indicator (by-product) during PCB manufacturing or is it a controlled component variable (additive)?

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#24286

Black Pad | 24 April, 2003

First, nickel is not used as a corrision resist in ENIG solderability protected pads. Left to its own devices, nickel corrodes and can be very tough to solder. The nickel is used as a barrier between the copper on the pad and the gold over-coat. If the nickel wasn't there, the copper of the pad would migrate into the gold. [Not long ago, putting rather thick gold, 2-3 microns, layer directly on copper, with no nickel barrier, was common in Britain, and met the British Telecom specs. But, we digress ...]

The general reaction for the deposition of electroless nickel is: 3NaH2PO2 + 3H2O + NiSO4 => 3NaH2PO3 + H2SO4 + 2H2 + Ni^0

Potassium is co-deposited with the nickel, as follows: H2PO2^- + Hads => H2O + OH^- + P 3H2PO2^- + P => H2PO3^- + H2O + 2OH^-

Nick Biunno gives a very short, over simplified summary: "Everybody looks at the nickel, but the cause [of black pad] turns out to be the immersion gold is too aggressive. The immersion gold works by corroding the nickel. If it is too aggressive it takes away the nickel and leave phosphorous behind. This makes it look like the phosphorous level is too high in the nickel bath."

For more: * Read �Are You In Control Of Your Electroless Nickel/Immersion Gold Process?� Kuldip Johal, Atotech USA Inc., Rock Hill, South Carolina [ kjohal@atousa.com ]; SMTA International; 09/30/2001 * Search the fine SMTnet Archives. There was a pretty good background thread about a month ago. [ http://www.smtnet.com/Forums/Index.cfm?CFApp=1&Message_ID=23346 ]

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razor

#24289

Black Pad | 25 April, 2003

Thanks for response. I do wish to qualify that I got the alleged role of Nickel use for corrosion resistance from an article authored by Jason Gjesvold, IS IT REALLY BLACK PAD?, "Phosphorus rich Ni alloys are often used for corrosion resistance during the highly acidic immersion gold (IG) process."

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#24290

Black Pad | 25 April, 2003

We accept your plea of innocence, but be careful. See, there is always someone out there trying to trick you.

Here are some pretty good articles: 8 Black pad articles: 8a Nick Biunno's article: http://www.nukcg.org/downloadfiles/Hadco%20on%20Immersion%20Gold%20failures.pdf

8b George Milad's article: http://www.circuitree.com/ct/cda/articleinformation/features/bnp__features__item/0,2133,11666,00.html

8c Ken Crouse's article: http://www.pcfab.com/db_area/archive/2002/0202/cullen.html

8d HP EADC investigation: http://www.nukcg.org/downloadfiles/Full%20HP%20Report%20on%20Imm.%20Gold%20Failures.pdf

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tommyg_fla

#24394

Black Pad | 2 May, 2003

Question for Dave F, in the following equation The general reaction for the deposition of electroless nickel is: 3NaH2PO2 + 3H2O + NiSO4 => 3NaH2PO3 + H2SO4 + 2H2 + Ni^0

Potassium is co-deposited with the nickel, as follows: H2PO2^- + Hads => H2O + OH^- + P 3H2PO2^- + P => H2PO3^- + H2O + 2OH^-

What is Hads?

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#24419

Black Pad | 6 May, 2003

Sorry everyone. There are more problems with the above response than not explaining "Hads": * Obviously it's not "potassium", but "phosphorous". * "3H2PO2^- + P => H2PO3^- + H2O + 2OH^-" is not balanced. It should be "3H2PO2^- => H2PO3^- + H2O + 2OH^- + 2P"

tommyg_fla

I'll respond your question, but I've got alligators up to here, and they're doing what alligators do.

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MA/NY DDave

#24423

Black Pad | 6 May, 2003

Hi

Our SMTnet buddy DaveyF already gave a better and faster reply than I can give at present. Let me give one answer to your question without checking DaveyF's formula which is probably a true equation.

DaveyF can always correct me.

As you can see by his Chemistry Equations P is an ingredient so it must be controlled to create the chemistry plating reaction. Gee my high school teacher would love me.

Here is a link to a periodic table. Sorry with more time I would do better due dilligence, and communication.

http://www.webelements.com/

YiEngr, MA/NY DDave

This message was posted Add this forum to your site! Click to learn more. the Electronics Forum @

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#24425

Black Pad | 6 May, 2003

tommyg_fla.

Sorry about being late getting back you.

Surface-active species, such as Fe2+, Mn2+, NH4+, and H+, can be adsorbed onto solid phases [and transported by things as weird as bioturbation or advection not that they have anything to do with what we're talking about]. The subscript "ads" refers to species adsorbed onto the solid surface, as distinct from those still in solution.

For more, look here: * http://www.erpt.org/012Q/NelsW-07.htm

* http://www.adsorption.com/publications/AdsorberDes2.pdf

Going into the ol' SMTnet Dictionary: * Absorption. See aDsorption (1) The retention of moisture by a substance. (2) The loss of light or heat as it passes through a material and is converted to heat or other forms of energy. * Adsorption. The adhesion of molecules to the surfaces of solids, as opposed to aBsorption, in which the molecules actually enter the absorbing medium. Charcoal, for example, which has a great surface area because of its porous nature, can adsorb large volumes of gases, including most of the poisonous ones, and thus is used in gas masks and filters.

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