Hi team - ok, I guess I'll go out and be the dissenting vote for this
discussion. First, none of the surface finishes we use today in the
electronic industry are perfect, they all have their own individual warts.
And George stated one detail very clearly - your first line of defense for
avoiding pwb surface finish problems is having a qualified board fabricator
who understands and manages their plating processes. As for ENIPIG - we
have been using the finish for over 12 years in an avionics product
environment with no issues. It still baffles me that the one industry
publication that stated tin/lead soldering and ENIPIG will result in
brittle solder joints is still cited. Yes, tin and palladium for a brittle
IMC (PdSn4) which can result in degraded solder joint integrity - tin and
gold form a brittle IMC (AuSn4) which can result in degraded solder joint
integrity and as an industry we deal with that aspect just fine so let's
please stop stating that ENIPIG and tin/lead are not compatible. Soldering
to palladium or gold containing surface finishes requires good process
control and adequate soldering process parameters.  I am in George's camp
as I am a fan of ImAg because soldering to copper is an inherently stronger
solder interface than soldering to nickel. However, ENIG is a good surface
finish with lots of applicability in many product use environments, we just
need to treat it right. I think Guy's solderability issues are plating
process related so JSTD-002/003 solderability testing supplemented by SEM
assessment may be in order to determine root cause.

Dave Hillman
Rockwell Collins
[log in to unmask]

On Tue, Jan 23, 2018 at 6:41 AM, Yuan-chia Joyce Koo <[log in to unmask]>
wrote:

> Agree with George 100%.  if you use Pb/Sn  solder and Pd containing
> finishing, you risk for brittle IMC in plate format... not sure about
> Pb-free... the Pb/Sn reaction with Pd formation of IMC is very fast if my
> memory serve me right.
> jk
> On Jan 22, 2018, at 6:39 PM, George Wenger wrote:
>
> Hi Guy,
>>
>> I'm a really old school soldering person.  There is nothing better than
>> SnPb soldering to an electroplated copper surface.  Also I still hate the
>> "Black Pad" name.  Black Pad isn't a failure mode it is a name given to
>> what you see after a failure.  Black Pad failures have been evaluated for
>> years and I still don't think they really have pinned down the cause for
>> the failure mode.  In my 45 years in the telecommunications industry the
>> one thing I learned is that solder joints made to electroless platings are
>> not as strong as solder joints made to electrolypic platings.  The attached
>> file (sorry TN will strip it but you will see it) lists some of the brittle
>> interface failures I've experienced during my years doing failure mode
>> analysis.  The common factor is solder joints made to electroless platings
>> are prone to brittle interface failures.  Although I've listed the
>> manufacturer in the attached list the failures are not due to the
>> manufacturer but to the type of surface finish. Other than immsersion tin
>> which and ENIG , which I really dislike, EPENIG is my other least favorite
>> surface finish.  It has three negatives (Pd and two electroless platings EP
>> and EN).  Pd as a top coating on a PCB does what Pd in a cars catalictic
>> converter does (i.e., it attacks crap out of the environment it is in) and
>> it is easily contaminated and loses it's solderability.  If you don't
>> dissolve all of the EPd you solder to an electroless Pd surface and if you
>> do you solder to an Eni  surface and those solder joints are not strong and
>> subject to brittle interface failure.
>>
>> I've always been a fan of IAg.  Yes silver oxidizes and yes silver
>> tarnishes but most of  the fluxes used in soldering can reduce the oxide
>> and tarnish and if the tarnish is really bad you know it by sight before
>> you do the soldering.  And the silver is so thin it dissolves into the
>> solder and you solder to the electroplated cooper below the immersion
>> silver so you have as strong a solder joint as possible.
>>
>>
>> So I'm not surprised that when you are using components with ENIG plating
>> and PCBs with EPENIG plating that you have a rash of soldering problems.
>>
>> Since you are using a WS Pb-free flux you really shouldn't be having
>> solderability issues unless your supplier is going a really crappy job and
>> your storage is terrible.  As for solder joint reliability  issues when
>> soldering to electroless platings you need to make sure you are doing
>> everything possible to make sure there is minimum stress on the solder
>> joint.  If not you are going to get "Black Pad" looking brittle interface
>> failures.
>>
>> -----Original Message-----
>> From: TechNet [mailto:[log in to unmask]] On Behalf Of Guy Ramsey
>> Sent: Monday, January 22, 2018 10:03 AM
>> To: [log in to unmask]
>> Subject: [TN] soldering problems
>>
>> So, is poor solderability like the flu . . .
>> We are having a rash of it.
>> We identified the EPENIG solder problem as a surface contaminate,
>> originating at the board house in the final rinse water.
>> We did not get to the bottom of the ENIG problem which I am thinking we
>> own.
>> Here is why.
>> The "black pads" may be found on either the board or the device. I have
>> attached a photo of each, one on the board and one on the device package.
>>
>> These are soldered with a WS Pb-free flux. We have carefully developed
>> the profile with  a long soak, to minimize the void problems on LGA. Ramp,
>> soak, and reflow are all within recommendations of the solder paste
>> manufacturer.
>>
>> Steve can you put these up for me. The problem does seem to be more
>> common on the DDR3 memory devices than any of the other BGA types.
>>
>