If youd don't include 'skip plating' below, then it may be four. We had a
very hard time to get rid of skip plating for mobile phones. I wrote this
short form then:
" common defect affecting the industry is 'skip plating', a phenomenon in
which, on an otherwise perfectly processed PCB, there are individual pads
that have an unacceptably thin nickel coating, or none at all. Several
causes of this fault are well known and understood. Definition of the
problem:
. Can be caused by contamination of the copper surface by solder resist
residues/etch resist residues (SnPb) and fingerprints.
. Inadequate activation by too low Pd content/temperature/exposure time
. Oxidation of the activated copper surface by prolonged rinsing
. Low activity of the electroless Ni bath can be caused by too low
temperature or wrong pH-level or insufficient bath loading
. Over-stabilization/contamination of the Ni bath
. Skip plating occurs only on PCBs coated with solder mask (!)
. Always affecting complete conductor chains. If one pad is inadequately
nickel plated, the same will apply to all other pads that are electrically
connected to it.
. Affects especially conductor chains or pads with smaller total area than
rest of board.
. Affects especially those conductor chains / pads that are in contact with
an imcompletely solder mask plugged via (!) "
/Inge
----- Original Message -----
From: "David D. Hillman" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Tuesday, October 12, 2010 9:17 PM
Subject: Re: [TN] Mech. damage or poor wetting?
> Hi Paul - It would be nice if we, as an industry, would be more
> descriptive in our root cause terms. When you run into the situation that
> Chris asked for everyone's input, there are three possible root causes to
> be investigated if the ENIG surface finish is suspect; (1) poor
> solderability due to incorrect plating processes; (2) brittle nickel
> interface failure due to assembly application and/or improper handling;
> (3) black pad due to incorrect plating processes. The big issue is that
> all three of these possible root causes are very similar to each other and
> require a detailed investigation to reveal which may be in play. I do not
> assign a root cause when chasing an ENIG solder joint failure until all of
> the situation data can be examined. As you detailed, sometimes a
> re-tinning operation can assist in determining which of the 3 root causes
> is in play.
>
> Dave Hillman
> Rockwell Collins
> [log in to unmask]
>
>
>
>
> Paul Edwards <[log in to unmask]>
> Sent by: TechNet <[log in to unmask]>
> 10/12/2010 12:59 PM
> Please respond to
> TechNet E-Mail Forum <[log in to unmask]>; Please respond to
> Paul Edwards <[log in to unmask]>
>
>
> To
> [log in to unmask]
> cc
>
> Subject
> Re: [TN] Mech. damage or poor wetting?
>
>
>
>
>
>
> I think this "black pad" label although, it is very visually descriptive
> of the defect, does not carry with it a singularly inclusive root cause...
>
>
> I have seen "black pad" caused by what appeared to be Ni metallization
> issues and by Ni oxidation/organic contamination...
>
> The Ni metallization issues were not re-workable without removing the Ni
> and the oxidation/contamination issue was solved by re-tinning...
>
> Any ideas as to what to call this problem so it reflects the root cause?
>
> Paul
>
> Paul Edwards
> Surface Art Engineering
>
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Phil Bavaro
> Sent: Tuesday, October 12, 2010 10:07 AM
> To: [log in to unmask]
> Subject: Re: [TN] Mech. damage or poor wetting?
>
> Thus.....etc
>
> I would want to inspect the rest of the board for more evidence of the
> black pad, such as the smaller chip caps....for it to only occur at the
> perimeter of the bga seems unlikely. On a chip cap pad which has had
> solderpaste melt and interact with the nickel underneath, the dewetting
> should be apparent.
>
> Dye and Pry can be misleading as to the cause of the dye penetration,
> especially when there are numerous possible mechanical questions.
>
> Phil
>
>
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D.
> Sent: Tuesday, October 12, 2010 9:40 AM
> To: [log in to unmask]
> Subject: Re: [TN] Mech. damage or poor wetting?
>
> It sure looks like Black Pad to me.
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Victor Hernandez
> Sent: Monday, October 11, 2010 2:41 PM
> To: [log in to unmask]
> Subject: Re: [TN] Mech. damage or poor wetting?
>
> Was this BGA reworked/repaired. Is it in close proximity to another
> BGA that was RW? Did the card/board see two consecutive thermal
> excursions?
>
>
> X"
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Thayer, Wayne - IIW
> Sent: Monday, October 11, 2010 1:55 PM
> To: [log in to unmask]
> Subject: Re: [TN] Mech. damage or poor wetting?
>
> Never mind. I just read the original post. I'm betting the whole
> shebang is due to poor wetting--that's why the correlation to the fanout
> escape.
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Thayer, Wayne - IIW
> Sent: Monday, October 11, 2010 2:52 PM
> To: [log in to unmask]
> Subject: Re: [TN] Mech. damage or poor wetting?
>
> What's going on with the picture of the cross section? The ball isn't
> wetting down the side of the plated pad.
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Chris Mahanna
> Sent: Monday, October 11, 2010 2:41 PM
> To: [log in to unmask]
> Subject: Re: [TN] Mech. damage or poor wetting?
>
> Here are a few pictures
> http://ipc-technet.groupsite.com/gallery/16011
>
> this job is a mixed bag. Currently we suspect soldering, cratering, ICT
> and t-cycling damage
>
> Chris
>
> From: [log in to unmask] [mailto:[log in to unmask]]
> Sent: Monday, October 11, 2010 2:22 PM
> To: TechNet E-Mail Forum; Chris Mahanna
> Cc: [log in to unmask]
> Subject: Re: [TN] Mech. damage or poor wetting?
>
>
> Hi Chris - do you have any pictures you can share?
>
> Dave Hillman
> Rockwell Collins
> [log in to unmask]
>
> Chris Mahanna <[log in to unmask]>
> Sent by: TechNet <[log in to unmask]>
>
> 10/11/2010 11:29 AM
> Please respond to
> TechNet E-Mail Forum <[log in to unmask]>; Please respond to
> Chris Mahanna <[log in to unmask]>
>
>
> To
>
> [log in to unmask]
>
> cc
>
> Subject
>
> [TN] Mech. damage or poor wetting?
>
>
>
>
>
>
>
> We have a BGA dye-n-pry job that shows board side sj damage with a
> strong correlation to fan-out clocking.
> We also have some microsection evidence of poor wetting.
> All damage/dye is on perimeters.
>
> Is this an indication of heat sinking and subpar wetting, or can it be
> completely mechanical? Both?
>
> Thanks
>
> Chris
>
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