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Printed Circuit Board Assembly & PCB Design Forum

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PCB Gold Plating

Steve T.

#5168

PCB Gold Plating | 7 February, 2001

I know this subject has been beat to death, but I need a clarification. I keep getting mixed messages about how much gold is required on a PCB for a reliable solder joint. Some people are saying 3 - 5 microns, some are saying 3 - 5 micro inches. Do all of you realize that these are two very different units of measurement? (A micron is a micro meter.) My board house is telling me I need to do 3 - 5 micro inches. This forum has suggested 3 - 5 microns. Somebody that "really" understands please clarify.

Thanks.

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#5177

PCB Gold Plating | 7 February, 2001

You're correct that some folk have used microns and other folks have used u" when discribing their ENIG specification. It's likely the the micron folks misquoted their units and it's arguable that participants in the forum should have taken them to task, but they didn't.

So, I guess it comes down to that this is just a bunch of folks' opinions. Some good, some bad.

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Doug Benefiel

#5205

PCB Gold Plating | 9 February, 2001

The ENIG process will yield between 3-7 micro inches (110 - 275 microns) of gold over the nickel barrier. This thickness range is pretty much the limit as this is a self limiting displacement reaction process. Once all surface nickel ions are replaced with gold, the reaction stops. However, with an electroless gold process, Au thickness can be as great as 40 micro inches. This is not desireable for soldered connections due to gold embrittlement as gold content reaches 3% of bulk solder joint volume. This is particularly concerning with SMT devices of finer geometry such as uBGA and CSP. The ENIG finish produces a very planar surface very suitable for repeatable solder paste printing. However, there are many issues that can affect the solderability and 2nd level reliability other than the gold thickness that also need to be considered. I.e. - Phoshporus conent of nickel, nickel plating rate, nickel thickness. Typicall board specifications call out nickel thicknes = 120 - 200 micro inches & gold thickness = 3 - 5 micro inches. I hope this helps.

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Steve T.

#5212

PCB Gold Plating | 12 February, 2001

Yes this does help. Thanks for your input.

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Dave E

#5311

PCB Gold Plating | 21 February, 2001

u" are smaller. 1uM = 39.4u" and so 3-7uM = 118-275u"

Then some articles or specs really confuse things by mixing mm and uM or using u all by itself...

http://www.circuitree.com/CDA/ArticleInformation/features/BNP__Features__Item/0,2133,11666,00.html

http://www.merix.com/resourcecntr/tech/smandenig.html

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