I'd call it Background plating. Most prevalent on soldermask when dealing
with ENIG.
Also, I'm not sure tape testing will identify black pad nickel. I have
lifted immersion gold from eless nickel with a tape test. The exposed nickel
surface looks black on the board and black on the backside of the tape/gold
layer( it just has to look dark and everyone and his brother will announce
"Black Pad".) Usually found on fully body ENIG (no soldermask) where
circulation/filtration flowrates were excessive and caused the lead
stabilizer present in the eless nickel to preferentially plate on the
copper, usually near circuit edges and ground planes physically located
nearest the solution spargers at the bottom of the tank. XRF at this area
shows very low nickel 40-90uin and less where 150-350uin was expected and
very large gold readings, 10-30uin where usual is 2-7uin. The gold cannot
adhere to the lead/nickel deposit and can be easily peeled with a tape test
before or after any additional baking. The surface at that area will also
resemble a matte looking striated area similar to 'scalloped' edges or short
fingers reaching into the panel (thats what led me to tape test when I first
encountered this phenomenon.) Reducing the flow rate of the filtration
system eliminated this problem completely. I can't describe the relief when
the root cause was found.
However, skip nickel plating is rather easy to see. On a panel directly off
of the production line tilted at an angle there is a marked difference with
the "look" of the gold plate. When panels are baked after ENIG to fully cure
LPI or legend ink or have sat overnight the copper/gold intermetallic is
formed and looks like a dark reddish pad. I appologize for not remembering
if the pads will look more shiny or more matte, I think more shiny because
the plated copper surface doesn't get uetched as it should during ENIG
process. I blame tin strip limititations leaving nitric acid or tin
compounds inside small holes which can poison the catalyst on the ENIG
process. As John wrote, smallholes and large aspect ratios.
Russ
>From: R Sedlak <[log in to unmask]>
>Reply-To: TechNet E-Mail Forum <[log in to unmask]>, R Sedlak
><[log in to unmask]>
>To: [log in to unmask]
>Subject: [TN] ENIG-Skip plating
>Date: Sat, 30 Apr 2005 11:59:10 -0700
>
>The "skip plating" you are referring to is a lack of plating where you
>wanted it?
>Is there a common name for plating occurring where you do NOT want it...?
>How common is this problem?
>
>Rudy Sedlak
>RD Chemical Company
>
>John Burke <[log in to unmask]> wrote:
>I actually developed a test panel to trigger skip plating at various hole
>sizes/aspect rations, it is designed to find the "edge" of the fluid
>dynamics of the particular bare process. The test panel allows you to
>assess
>the line capability for high aspect ratio , thick board - small via boards,
>but like I said before you need to understand whether you are working with
>a
>skip plate problem OR a straight black pad chemistry issue.
>
>John
>
>-----Original Message-----
>From: TechNet [mailto:[log in to unmask]]On Behalf Of Vladimir Igoshev
>Sent: Friday, April 29, 2005 11:17 AM
>To: [log in to unmask]
>Subject: Re: [TN] gold vs copper plating on pcb's - Black PAD???
>
>
>If it's not the worst-worst case when the IPC test would work, then I'd say
>no. If one knew how to do it, then the person would be pretty rich, I
>guess.
>:-)
>
>Vladimir
>
>Vladimir Igoshev, Ph. D.
>Senior Materials Researcher
>Research in Motion
>451 Phillip St.
>Waterloo, ON, N2L 3X2
>
>Voice: (+1) 519-888-7465, ext. 5283
>Fax: (+1) 519-886-0863
>E-mail: [log in to unmask]
>
>
>-----Original Message-----
>From: TechNet [mailto:[log in to unmask]]On Behalf Of Kanaiyalal Patel
>Sent: Friday, April 29, 2005 1:34 PM
>To: [log in to unmask]
>Subject: Re: [TN] gold vs copper plating on pcb's - Black PAD???
>
>
>Vladimir and others,
>Are you saying that I may not be able to find out
>black pad condition on fab before relfow?
>
>re,
>Ken Patel
>
>--- Vladimir Igoshev wrote:
>
> > Yes, after reflow.
> > Regards,
> > Vladimir
> > Sent from my Blackberry Wireless
> > Vladimir Igoshev, 519-888-7465 ext.5283
> >
> >
> > -----Original Message-----
> > From: TechNet
> > To: [log in to unmask]
> > Sent: Fri Apr 29 12:17:00 2005
> > Subject: Re: [TN] gold vs copper plating on pcb's -
> > Black PAD???
> >
> > All,
> > How is to detect black pad? Can it be inspected at
> > PCB
> > level? I guess no. Is it the after reflow soldering
> > phenomena?
> >
> > Re,
> > Ken Patel
> >
> >
> > --- Werner Engelmaier wrote:
> > > Hi Bob,
> > > First, with ENIG you do not solder to gold, but to
> > > the underlying nickel;
> > > Second, soldering to Ni requires more thermal
> > > energy, thus higher temperatures, and that is
> > really
> > > bad news on top of the T-increase necessary for
> > > LF-solders;
> > > Third, the 'black pad' issue will not go away with
> > > LF-solderas,but actually may become worse.
> > > Thus, Immersion Ag is a good choice.
> > > Werner Engelmaier
> > >
> > > -----Original Message-----
> > > From: Jeffrey Bush
> > > To: [log in to unmask]
> > > Sent: Wed, 27 Apr 2005 07:14:42 -0400
> > > Subject: Re: [TN] gold vs copper plating on pcb's
> > >
> > >
> > > If you stick with ENIG and do not test Immersion
> > > Silver then I am sure
> > > you will be doing future testing to combat the
> > > issues with ENIG. Monies
> > > are being put into the development if silver and
> > > several toughed
> > > formulas are coming out that have excellent
> > > resistance to TC and do not
> > > have the issues associated with ENIG. OSP is also
> > > seeing some
> > > development, but I do not see this as a viable
> > > alternative today.
> > >
> > > Jeffrey Bush
> > > Director, Quality Assurance and Technical Support
> > >
> > > VERMONT CIRCUITS INCORPORATED
> > > 76 Technology Drive - POB 1890
> > > Brattleboro, Vermont 05302
> > > Voice: 802.257.4571.21 Fax: 802.257.0011
> > > http://www.vtcircuits.com
> > >
> > >
> > > -----Original Message-----
> > > From: Bob Arciolla [mailto:[log in to unmask]]
> > > Sent: Tuesday, April 26, 2005 4:41 PM
> > > To: [log in to unmask]
> > > Subject: [TN] gold vs copper plating on pcb's
> > >
> > > Good Afternoon all,
> > >
> > > Our company will be switching over to lead free
> > and
> > > we have received
> > > sample pcb's from one of our vendors and one board
> > > has gold (ENIG) for
> > > the traces and one has copper (OSP). From some of
> > > the emails I have seen
> > > on Technet it appears that gold is what most of
> > > companies are going to
> > > be using? Is this correct or is there some other
> > > materials we should be
> > > looking into to use? Is the gold more reliable
> > than
> > > the copper?
> > > Any input would be greatly appreciated.
> > >
> > >
> > >
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