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Black Pad?? (PICTURES)

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#57004

Black Pad?? (PICTURES) | 20 October, 2008

Good morning all, we have been having some random intermittent connections on some BGAs lately on ENIG finished boards. Can you take a quick look at this picture (link) and let me know if it looks like a possible black pad occurrence? The picture shows the pads after the part has been removed and cleaned using solder wick. The operator says this is normally what she sees when there is a BGA problem.

Oh yea, paste is/was Alpha OM-5100 NC

http://img408.imageshack.us/img408/6311/1002347qp8.jpg

http://img133.imageshack.us/img133/1424/1002349em4.jpg

Thanks in advance JD

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#57005

Black Pad?? (PICTURES) | 20 October, 2008

Any pictures of those pads prior to printing? Or how does the incoming boards look?

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#57006

Black Pad?? (PICTURES) | 20 October, 2008

No pictures pre-paste. I have noticed on a few occasions a couple of boards that look like they have a slight discoloration on some areas of the board. Kind of like a shadow almost on the gold.

Josh

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#57007

Black Pad?? (PICTURES) | 20 October, 2008

Picture (img133) sure looks like black pad. Maybe you can compare the pic's yourself with the pictures in the ITRI Report on black pad.

http://www.pwbrc.org/members/pdf/works99/Houghton.PDF

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#57008

Black Pad?? (PICTURES) | 20 October, 2008

The discoloration/shadow appearance is a clear sign of black pad which is from nickel corrosion in the gold bath.

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#57009

Black Pad?? (PICTURES) | 20 October, 2008

Yup, just read that in the link Patrick sent. Thanks again... Im going to have everyone screen the boards for this carefully before processing. I have also sent the board manufacturer an email to get their comment on the matter. No PCB vendor thinks they are ever at fault though. Should they deny any wrong doing, what is the best method of testing? Can it be done post assembly or do the boards have to be bare?

Thanks JD

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#57011

Black Pad?? (PICTURES) | 20 October, 2008

> Yup, just read that in the link Patrick sent. > Thanks again... Im going to have everyone screen > the boards for this carefully before processing. > I have also sent the board manufacturer an email > to get their comment on the matter. No PCB vendor > thinks they are ever at fault though. Should they > deny any wrong doing, what is the best method of > testing? Can it be done post assembly or do the > boards have to be bare? > > Thanks JD

I don't think there is any testing to prove any wrong doing. It could be a design issue if it is repetitive on the same pads. I could be ENiG process or from soldermask process if it is done prior to ENiG.

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#57013

Black Pad?? (PICTURES) | 20 October, 2008

Josh,

You can not check the bare boards for black pad unless you remove the gold plating. Like Robin said black pad is nickel oxidation/corrosion and a result from bad electroless nickel plating bath control. The only preventative action you take is checking the board vendors for black pad history.

This proves again how reliable lead free really is (sorry couldn't resist).

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#57014

Black Pad?? (PICTURES) | 20 October, 2008

Josh

From looking at your pix, we don't have a clue. [And we're going down to the nurse's station to get our eye checked because we don't black bubkus.] More than anything else the: * White on the pads could be solder * Copper-penny brown on the pads could be CuO

On analyzing black pad boards, look here http://www.empf.org/empfasis/feb04/0204help.htm

Here's what hypercorroded [black pad] nickel looks like http://www.smtnet.com/forums/Index.cfm?CFApp=1&Message_ID=53319

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#57015

Black Pad?? (PICTURES) | 20 October, 2008

Patrick

You're correct that black pad analysis is a distructive test.

Kicking the lead-free dog certainly is easy [and somewhat fun] to do, but black pad is an equal opportunity defect. It affects leaded boards as well as it does with lead-free.

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#57023

Black Pad?? (PICTURES) | 21 October, 2008

Dave,

I know that black pad isn't solderable by any alloy. But it's still justified to relate the nickel barrier plated boards to lead free. Before lead free the predominant board plating was HASL and OSP. These platings disappeared with the switch to lead free because of copper dissolution.

I will always remember (in a previous life) our board shop decided to switch from chemical lead/tin plating and reflow to nickel/bright tin what a nightmare that was.

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