A similar effect can be design related.
Sometimes the "black pad" effect can be mistakenly named that when it is
actually a case of skip plating.
Skip plating can have 2 results, one where the pad skips nickel completely
and the gold is deposited straight onto copper and which then diffuses into
the copper giving the typical "skip plate" effect. The second effect is
where the nickel deposit is very thin and ends up hyper corroded by the gold
chemistry giving rise to the erroneous call of "black pad".
Skip plating in this respect is caused by tin residues left in the via holes
effectively "poisoning" the nickel deposition onto the copper. This can be
heavily influenced by design where aspect ratios are high and holes are
small.
As an example it will kick in at drilled hole sizes of around 10 mils in
aspect ratios of over 10 to 1.
Kind regards,
John Burke.
------------------------------------
Avanex
John Burke
Senior Manager RoHS Compliance
[log in to unmask]
40919 Encyclopedia Circle
Fremont
CA 94538
tel: 510 897 4250
fax: 510 979 0189
mobile: 510 676 6312
------------------------------------
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Cheryl Johnson
Sent: Friday, August 12, 2005 10:20 AM
To: [log in to unmask]
Subject: [TN] osp vs enig, black pad... - renamed
Ellsworth,
Thank you for your help. My biggest concern with the osp is that we have 18
contact pads, that must remain absolutely flat (so we are not wanting to
just add solderpaste to them), so they need to be plated any way.
With OSP, how would you recommend handling our contact pads? Having 2
processes would most likely void any potential cost savings..
Several years ago, when we were concerned with "black pad", I receive this
information:
"Black pad is the result of too high phosphorous content of the nickel bath
and the organic leach out from the solder mask coating. If the phosphorous
content is too high in the nickel coating Black Pad may result during
thermal excursion in assembly. Suppliers of immersion gold have performed
extensive testing to create the condition and remedies to eliminate the
problem. They have reformulated the chemistries to better stabilize the
prosperous levels and revised analytical and bath maintenance schedules at
the user site.
Solder mask is also known to be a contributor to black pad. Typical
processing techniques allow for solder mask to be applied over the bare
copper conductors prior to electroless nickel and immersion gold. We have
heard of cases where the solder mask has contaminated the nickel bath with
organics or leach out from the solder mask. The cause for the condition can
be in the incompatibility of the solder mask and immersion gold process. A
number of solder mask types have been reformulated and designated as
"compatible" with immersion gold.
It is important to emphasize adequate bath maintenance schedules to reduce
the potential for the formation of Black Pad."
As black pad is a process related issue, we believe our process has it under
control (we have not had any issues.)
Sincerely,
-----------------------------------
Cheryl Johnson, C.I.D.+
Manager
ExcelStor US Office, Engineering Services
Email: [log in to unmask]
Tel: (303) 684-7291
Fax: (303) 684-7268
Mobile: (303) 809-5815
-----------------------------------
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Ellsworth Berkowitz
Sent: Friday, August 12, 2005 9:02 AM
To: [log in to unmask]
Subject: Re: [TN] <Misc>Re: [TN] <Misc>Re: [TN] RoHs board surface
recommendations.
In the early '97 timeframe we switched from HASL to ENIG, primarily to
achieve "flat pads" for the increasing use of fine pitch & BGAs in our
designs. Within several months of ENIG implementation, however, we
experienced the "black pad" phenomenon. We went into scramble mode to find
an alternative...
After attending the IPC Surface Finishes conference that year, we selected
OSP as our first choice finish. Immersion Ag looked very promising but we
didn't believe it was as widely available; we did continue to monitor
developments with this finish.
OSP has worked very well in our process over these years. We started to
migrate to immersion Ag in the past year, however, mostly due to issues with
ICT probing of OSP test point pads. As the complexity of our products has
increased, the designs have likewise migrated from reflow-wave to
double-sided reflow & selective solder. Wave solder more effectively
prepares the OSP test point for probing; solder paste & reflow presents more
challenge to consistently cover our typical via-in-pad test points. A whole
'nother story...
Generally we have reasonable inventory turnover, so OSP aging & degradation
over time hasn't been a problem (in a few cases of slow moving product, we
sent boards out to be re-OSP'ed). We have linked lines, so, when a work
order starts it stays on the line until all assembly & soldering is finished
(the chance for external Cu to oxidize after exposure to multiple thermal
processes is therefore very limited; our boards don't wait in lengthy
queue's after reflow or glue cure). Also, we don't bake boards.
Solder joint integrity is excellent with OSP.
We still specify OSP on low complexity designs (very few of those
anymore...).
Immersion Ag is working well; also, cost has been on par with OSP (our buyer
does a great job working with the suppliers).
Hope this helps. Contact me off-line if you have other questions.
Ellsworth D. Berkowitz, P.E.
On Thu, 11 Aug 2005 14:49:08 -0600, Cheryl Johnson
<[log in to unmask]> wrote:
>Well I am a wife, don't have a tail (hair down to my waist, though...)
>In any case, I have been using ENIG for several years with no problems.
>
>HOWEVER, recently our off shore fab house is wanting us to go to "OSP over
>copper".
>
>Any comments? Thank you!
>
>Sincerely,
>-----------------------------------
>Cheryl Johnson, C.I.D.+
>Manager
>ExcelStor US Office, Engineering Services
>Email: [log in to unmask]
>Tel: (303) 684-7291
>Fax: (303) 684-7268
>Mobile: (303) 809-5815
>-----------------------------------
>
>
>-----Original Message-----
>From: TechNet [mailto:[log in to unmask]]On Behalf Of John Burke
>Sent: Thursday, August 11, 2005 1:16 PM
>To: [log in to unmask]
>Subject: Re: [TN] <Misc>Re: [TN] <Misc>Re: [TN] RoHs board surface
>recommendations.
>
>
>Yup.......................
>
>Lets change the chemistry topic...............Ice cream anyone??
>
>John
>
>------------------------------------
>Avanex
>John Burke
>Senior Manager RoHS Compliance
>[log in to unmask]
>40919 Encyclopedia Circle
>Fremont
>CA 94538
>tel: 510 897 4250
>fax: 510 979 0189
>mobile: 510 676 6312
>------------------------------------
>
>
>-----Original Message-----
>From: TechNet [mailto:[log in to unmask]]On Behalf Of Stadem, Richard
>Sent: Thursday, August 11, 2005 1:09 PM
>To: [log in to unmask]
>Subject: Re: [TN] <Misc>Re: [TN] <Misc>Re: [TN] RoHs board surface
>recommendations.
>
>
>It must be Friday for some of us:)
>
>-----Original Message-----
>From: TechNet [mailto:[log in to unmask]] On Behalf Of Chris Ball
>Sent: Thursday, August 11, 2005 2:48 PM
>To: [log in to unmask]
>Subject: Re: [TN] <Misc>Re: [TN] <Misc>Re: [TN] RoHs board surface
>recommendations.
>
>......unnnnh........no tail.......wife..........must
>resist.........arrrrgh....
>
>
>
>
> Steve Hodge
> <[log in to unmask]> To:
>[log in to unmask]
> Sent by: TechNet cc:
> <[log in to unmask]> Subject: Re:
>[TN] <Misc>Re: [TN]
> <Misc>Re:
>[TN] RoHs board surface
> 08/11/2005 03:36 PM
>recommendations.
> Please respond to TechNet
> E-Mail Forum; Please
> respond to Steve Hodge
>
>
>
>
>
>
>
>George, I am sorry you feel you have to downgrade my opinion as being a
>sales pitch or "wife's tail". I am stating data -substantiated facts and
>I could care less about selling something to you or anyone else. A
>wife's tail? What? My wife does not have a tail. I think it should be
>"wive's tale" anyway.
>
>At 12:30 PM 08/11/2005, you wrote:
>>John,
>>
>>Your opinionated! but then too so am I. However, it sounds like our
>>opinions are based on data and not "wife's tails" or "sales pitches"
>>
>>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 John Burke
>>Sent: Thursday, August 11, 2005 2:16 PM
>>To: [log in to unmask]
>>Subject: Re: [TN] <Misc>Re: [TN] RoHs board surface recommendations.
>>
>>
>>Very nice,
>>
>>Until you consider that ENIG infringes the design rules for at least
>>one
>of
>>the top 3 global CM's due to the issues associated with it.
>>
>>If you want the number of their chief technologist who has to look at
>enigma
>>failures week in week out I will happily supply details off line.
>>
>>I personally have built hundreds of thousands of assemblies on ENIG as
>well
>>as Immersion AG.
>>
>>As for the rest, HASL is generally failure related to a complete lack
>>of understanding of tin thickness and intermetallic growth rate, OSP
>>failures generally are related to not understanding the degradation of
>>that finish with multiple reflow cycling, and personally I would never
>>use immersion
>tin
>>without some type of diffusion barrier between it and the copper if nay
>time
>>in storage was to be considered.
>>
>>The ENIG when it fails can be catastrophic............and in most cases
>can
>>be pointed back to the process at the fab house rather than what
>>happened
>to
>>it during the assembly process, unlike most of the other finish
>>defects,
>and
>>has to my knowledge resulted in multi million dollar lawsuits between
>>companies in the bay area due to failures.
>>
>>If it doesn't fail - it is fine, but the joint shear strength is less
>>than the equivalent HASL or immersion AG finish due to the Tin
>>nickel/nickel copper crystalline structure, so taking into
>>consideration the higher temperatures of lead free I would be vary
>>careful using it for area array packages using this soldering
>technology.
>>
>>For the record have been using immersion silver since 1996 as I
>>produced
>the
>>first beta site production runs using alpha level, so perhaps my views
>have
>>a little more history.
>>
>>Call me opinionated - I'll take it.
>>
>>John
>>
>>
>>
>>
>>
>>
>>
>>------------------------------------
>>Avanex
>>John Burke
>>Senior Manager RoHS Compliance
>>[log in to unmask]
>>40919 Encyclopedia Circle
>>Fremont
>>CA 94538
>>tel: 510 897 4250
>>fax: 510 979 0189
>>mobile: 510 676 6312
>>------------------------------------
>>
>>
>>-----Original Message-----
>>From: Steve Hodge [mailto:[log in to unmask]]
>>Sent: Thursday, August 11, 2005 10:44 AM
>>To: TechNet E-Mail Forum; John Burke
>>Subject: Re: <Misc>Re: [TN] RoHs board surface recommendations.
>>
>>
>>John, come on now. Anything can happen at any time. I have seen some
>>reservations from the IS users as to silver migration possibilities and
>
>>shelf life/handling issues --you might say they have not seen them
>--"yet".
>>I have had more problems with HASL, OSP and IT than I have with ENIG.
>>ENIG has longer data history than IS, so both shoes have already
>>dropped so to speak. Three years without problems, is an eternity in
>>this business, especially when we are expected to build custom
>products in 24 hours.
>>
>>
>>At 11:00 AM 08/11/2005, you wrote:
>> >with it............YET..........
>> >
>> >------------------------------------
>> >Avanex
>> >John Burke
>> >Senior Manager RoHS Compliance
>> >[log in to unmask]
>> >40919 Encyclopedia Circle
>> >Fremont
>> >CA 94538
>> >tel: 510 897 4250
>> >fax: 510 979 0189
>> >mobile: 510 676 6312
>> >------------------------------------
>> >
>> >
>> >-----Original Message-----
>> >From: TechNet [mailto:[log in to unmask]]On Behalf Of Edwin Louis
>> >Sent: Thursday, August 11, 2005 4:48 AM
>> >To: [log in to unmask]
>> >Subject: Re: [TN] RoHs board surface recommendations.
>> >
>> >
>> >We have been using ENIG now for about three years and have had no bad
>
>> >experiences with it. NASA for one does not allow the use of silver .
>> >
>> >-----Original Message-----
>> >From: TechNet [mailto:[log in to unmask]] On Behalf Of Werner Engelmaier
>> >Sent: Wednesday, August 10, 2005 4:57 PM
>> >To: [log in to unmask]
>> >Subject: Re: [TN] RoHs board surface recommendations.
>> >
>> >Hi Steve,
>> >I do not know about "bad-mouth ENIG"--I am a reliability consultant,
>> >and have had plenty of calls because of ENIG related failures, but
>> >not a one
>about
>> >iAg. On the other hand, I do not know about their respective
>environmental
>> >implications.
>> >
>> >Regards,
>> >Werner Engelmaier
>> >Engelmaier Associates, L.C.
>> >Electronic Packaging, Interconnection and Reliability Consulting
>> >7 Jasmine Run
>> >Ormond Beach, FL 32174 USA
>> >Phone: 386-437-8747, Fax: 386-437-8737, Cell: 386-316-5904
>> >E-mail: [log in to unmask], Website: www.engelmaier.com
>> >
>> >
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