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June 2005

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Subject:
From:
"Wenger, George M." <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Wenger, George M.
Date:
Wed, 8 Jun 2005 11:30:26 -0400
Content-Type:
text/plain
Parts/Attachments:
text/plain (262 lines)
Michel,

I'm not going to tell you that you have "Black Pad" or "Black Line Nickel" because I hate those names.  They describe an appearance rather than a failure mode.  Everything you've said so far indicates that you are experiencing the brittle interface failures that have been associated with ENIG.  If so there isn't much you can do.  If there are non-populated pads on your board, or for that matter faducials that have ENIG plating, I would measure the gold and nickel plating thickness with XRF.  One of the resent recommendations that I believe has been incorporated in the new IPC ENIG spec ( I don't remember the number but it something like IPC-4552)is for the gold plating thickness to be below 2 microinches.

As a side note,I'm not an advocate of using solder wick to clean pads especially on ENIG pads.  This process can wick-off all of the solderable "Free Tin-lead Solder" and leave behind only intermetallic compounds which if they oxidze aren't solderable using the fluxes typically used for assembly.  Using a solder-sucker seems to pull off the excess sodler but leaves behind enough "Free Tin-lead" to keep the intermetallics covered and thus preserves the pad sodlerability.

Regards,
George
George M. Wenger
Reliability / FMA Engineer
Base Station and Subsystems Group
Andrew Corporation, 40 Technology Drive, Warren, NJ 07059 (908) 546-4531 [log in to unmask]


-----Original Message-----
From: Arbour, Michel [mailto:[log in to unmask]]
Sent: Wednesday, June 08, 2005 11:15 AM
To: Wenger, George M.; TechNet E-Mail Forum
Subject: RE: [TN] Solderability issues with ENIG finish


You are right on it. They did not pass functional test then we tried to
replace the BGA.

MIchel

-----Original Message-----
From: Wenger, George M. [mailto:[log in to unmask]]
Sent: Wednesday, June 08, 2005 11:11 AM
To: TechNet E-Mail Forum; Arbour, Michel
Subject: RE: [TN] Solderability issues with ENIG finish


Michel,

I'm not sure that the conclusion the analyest made that since there was no
mud cracking seen at
Area A that black nickel was most likely not present.  The analysis and
photographs are certainly consistent with the brittle interface fractures
experienced with ENIG.  How did you discover this issue?  We're you boards
having problems passing functional test and subsequently were BGA's being
replaced?

Regards,
George
George M. Wenger
Reliability / FMA Engineer
Base Station and Subsystems Group
Andrew Corporation, 40 Technology Drive, Warren, NJ 07059 (908) 546-4531
[log in to unmask]


-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Arbour, Michel
Sent: Wednesday, June 08, 2005 10:56 AM
To: [log in to unmask]
Subject: Re: [TN] Solderability issues with ENIG finish


In our case, it does not correlate to pad size, we've had a few 0603 and
0.020" pitch pads with the same defect.



-----Original Message-----
From: Kathy Kuhlow [mailto:[log in to unmask]]
Sent: Wednesday, June 08, 2005 10:50 AM
To: [log in to unmask]
Subject: Re: [TN] Solderability issues with ENIG finish


What was the size of the BGA pad does this issue correlate to pad size? Does
anyone have background info on ENIG finish and BGA sites in particular?  I
have been going through the archives looking for that answer.

Kat

>>> [log in to unmask] 6/8/2005 9:44:57 AM >>>
The pad was populated (BGA) and the component was removed. The BGA land was
cleaned with solder wick braids and at that moment the operator noticed that
the pad did not wet completely.
The solder wick braid is composed of Rosin 2-10% and copper .



-----Original Message-----
From: Wenger, George M. [mailto:[log in to unmask]]
Sent: Wednesday, June 08, 2005 10:16 AM
To: TechNet E-Mail Forum; Arbour, Michel
Subject: RE: [TN] Solderability issues with ENIG finish


Michel,

I'll wait to comment until after I look at the picture once it is posted on
Steve's web page but I couldn't tell from your description if there was a
component on the pad and if so was it removed or was the pad that was
examined a non-populated pad?

Regards,
George
George M. Wenger
Reliability / FMA Engineer
Base Station and Subsystems Group
Andrew Corporation, 40 Technology Drive, Warren, NJ 07059 (908) 546-4531
[log in to unmask]


-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Arbour, Michel
Sent: Wednesday, June 08, 2005 9:48 AM
To: [log in to unmask]
Subject: [TN] Solderability issues with ENIG finish


> Hi ,
> We've been having some solderability problems with one of our supplier. A
> populated PCB was sent for elementary analysis and we got the results back
> from the lab.
> Before going further in the corrective action process i would like to know
> if some of you agree and support the conclusions of the report based on
> the following data.
>
> - The board sent to analysis was populated , one half of a smt pad  did
> not wet with solder the other half wetted properly
> - The problem was noticeable on approx. 2% of the lot of PCB. 2-3 pads per
> board
> - The pad could not be soldered using an iron pen
> - Solder paste is standard Sn63, Pb37
>
> Two area on the pad were analyzed, one that was wetted , the other was
> not.
> Concentrations of element found  were the following
> - On the wetted area of the pad ALIAS : "AREA B"
> 5.40% C
> 2.04% N
> 0.81% O
> 45.32% Sn
> 2.45% Ni
> 3.67% Cu
> 40.31% Pb
>
> On the unsolderable area of the pad ALIAS "AREA A"
> 6.08% C
> 9.08% P
> 9.55% Sn
> 66.62% Ni
> 3.47% Cu
> 5.20% Au
>
> The conclusion of the report states :
> Area A is a fracture surface at the intermetallic boundary while Area B is
> a fracture surface at or near the bulk solder.  No mud cracking is seen at
> Area A which indicates that black nickel was most likely not present.  The
> fact that there is a fairly large gold peak at area A indicates that there
> may not have been sufficient time to adequately form the solder joint as
> the gold may not have had time to diffuse into the bulk solder.
>
> I can post a picture of the pad if you can point me to a location
>
>
> Michel Arbour
> Kontron Canada Inc.
>

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