Hi Wayne - since we had already mentioned black pad, I figured we didn't
want to scare Murray with too many horror stories. And since he was
actually looking at an ENIG finish, the issue of gold embrittlement should
be very low unless he would have a heavy gold component case as you
described.

Dave Hillman
Collins Aerospace
[log in to unmask]

On Mon, Jan 6, 2020 at 2:05 PM Wayne Thayer <[log in to unmask]> wrote:

> Coming in late, but did anybody mention gold embrittlement? I know we've
> seen (in this forum) pictures of gold plated pads which only partially wet
> because the ratio of tin to gold was low enough that the melting point at
> the "wetting front" went above the temperature in the reflow oven. Too much
> gold is a bad thing! I see this frequently with RF devices in ceramic
> packages, where they wanted 30-50 micro inches of gold on wirebond pads, so
> they just make that the spec for the whole shooting match. Since there
> isn't much solder in the pads for these devices (often QFN), then you end
> up with embrittlement unless you pay one of our friends to solder dip the
> parts first.
>
> Wayne Thayer
>
> On Mon, Jan 6, 2020 at 11:46 AM Decker, Scott Collins <
> [log in to unmask]> wrote:
>
> > Dennis,
> >     That's the best descriptions I've seen in a long time! Thanks for the
> > process descriptions, now I can remember them too... :-) Well,
> hopefully...
> > Later...
> >
> > Scott Decker | Senior Engineer, PCB Design Services CID+ | Electronic
> > Systems Center
> > COLLINS AEROSPACE
> > 3445 S. 5th Street, Suite 170, Phoenix, AZ 85040 U.S.A.
> > Tel: 602 308 5957  FAX: 602 243 2347
> > [log in to unmask]  www.collinsaerospace.com [collinsaerospace.com
> ]
> > KE7MWT
> > CONFIDENTIALITY WARNING: This message may contain proprietary and/or
> > privileged information of
> > Collins Aerospace Systems and its affiliated companies. If you are not
> the
> > intended recipient please 1) do not disclose, copy,
> > distribute or use this message or its contents, 2) advise the sender by
> > return e-mail, and 3) delete all copies (including all
> > attachments) from your computer. Your cooperation is greatly appreciated.
> >
> > -----Original Message-----
> > From: TechNet [mailto:[log in to unmask]] On Behalf Of Dennis Fritz
> > Sent: Monday, January 6, 2020 12:46 PM
> > To: [log in to unmask]
> > Subject: Re: [TN] [External] [TN] immersion gold thickness
> >
> > Murray,
> > I suspect you are inter-mingling three kinds of plating - electroplate,
> > electroless plate, and immersion plate.  All can deposit gold.
> >
> > Electroplate is driven by an external electrical  voltage source and can
> > plate any thickness you want - easily 15 microinches if you can afford
> the
> > gold cost.   That is the oldest circuit board plating process, and is
> still
> > used for the connector contact "fingers" of circuit boards.   However, it
> > does require all the circuitry to be plated must be in electrical contact
> > with the voltage source.
> >
> > Electroless plating is "chemical" plating where two chemicals react and
> > release electrons to cause dissolved gold salts in the bath to deposit on
> > surfaces.  Electroless plating comes in two forms, depending on the bath
> > chemistry.  Catalyized electroless depends on some very thin surface
> layer
> > of a catalytic metal - like palladium - to cause the chemical reaction
> that
> > releases electrons resulting in metal deposition.  Auto-catalytic
> > electroless enables the deposited metal to further the chemical reaction
> > between the reduction chemicals - building potentially thick deposits of
> > metals.   However, autocatylitic electroless is much slower than
> > electropate, and also eats up reactant chemicals - much more expensive
> > than electrical current.
> >
> > The final plating is "immersion".  This is a chemical replacement
> reaction
> > - based on the electromotive (battery) potential. One metal is dissolved
> > and gives up electrons to chemically reduce another metal in solution.
> >  That is in the case of ELECTROLESS nickel IMMERSION gold (ENIG), that
> the
> > electrolessly deposited nickel is dissolved into a gold solution and gold
> > deposits on the surface of the nickel.  The reacation stops (thickness is
> > limited), when the dissolved gold salts in solution cannot find any more
> > available surface nickel to dissolve.
> >
> > The dissolution of the electroless nickel is essentially corrosion.
> > Excess immersion gold leaves a porous, corroded nickel underlayer - that
> is
> > generally called black pad because of its color and corroded appearance.
> >
> > Hope this helps.
> > Denny Fritz
> >
> > On Mon, Jan 6, 2020 at 11:42 AM Campbell, Murray <
> [log in to unmask]
> > >
> > wrote:
> >
> > > My original question came out of curiosity from one of Lee Ritchies
> > > fab notes stating a max of 15 micro inches of electroplated gold be
> > > applied over electroplated nickel.  We had historically called for a
> > > max of 8 micro inches of immersion gold to be applied.  I was curious
> > > why either max would be called out and why as I would prefer to just
> > > call out the min requirement as per 4552
> > >
> > > -----Original Message-----
> > > From: TechNet <[log in to unmask]> On Behalf Of Stadem, Richard D
> > > Sent: Monday, January 6, 2020 7:36 AM
> > > To: [log in to unmask]
> > > Subject: Re: [TN] [External] [TN] immersion gold thickness
> > >
> > > In addition to the black pad issues Dave mentioned, the 5 uinch limit
> > > was also to provide sufficient plating thickness to prevent oxidation
> > > of the underlying nickel, which is what you actually solder to, as
> > > well as prevent gold embrittlement in the final solder joints.
> > > At least 2 uinches is required to provide the protection, but you
> > > certainly do not want anything over 5, and never 15 uinches. I am not
> > > even sure it is possible to get 15 uinches in an immersion plating
> > > process. But whatever process that gives you 15 uinches is NOT
> > > electroless nicker/immersion gold.
> > > Odin
> > >
> > > -----Original Message-----
> > > From: TechNet <[log in to unmask]> On Behalf Of David Hillman
> > > Sent: Friday, January 3, 2020 3:44 PM
> > > To: [log in to unmask]
> > > Subject: Re: [TN] [External] [TN] immersion gold thickness
> > >
> > > Hi Murray - if you can get a true ENIG plating chemistry to put 15
> > > inches of gold thickness on a board, you would never want to use the
> > > board as the gold plating would have severe structure and/or
> > > solderability issues. The
> > > IPC-4552 specification contains the industry consensus gold plating
> > > thickness range that applies to producing an acceptable and reliable
> > > ENIG plating layer. Any gold plating thickness outside of that range
> > > would be questionable at best for quality and reliability unless you
> > > are working closely with a plating chemistry supplier who is doing a
> > > custom plating bath composition. One of the early issues of ENIG
> > > plating was the industry asking the plating chemistry suppliers to
> > > provide an immersion gold plating thickness that exceeded the
> > > acceptable physics of the plating chemistry (basically this is how we
> > discovered "black pad"!).
> > >
> > > Dave Hillman
> > > Collins Aerospace
> > > [log in to unmask]
> > >
> > > On Fri, Jan 3, 2020 at 3:30 PM Campbell, Murray
> > > <[log in to unmask]>
> > > wrote:
> > >
> > > > Happy New Year All,
> > > >
> > > > Is there any good reason to call out a maximum gold thickness /
> > > > nickel thickness on fab notes or is it sufficient to rely on simply
> > > > stating that the fabricator shall follow ipc-4552 minimum thickness?
> > > > I have seen some companies state that a maximum thickness upwards of
> > > > 15 µin to be acceptable.  Is there any value in stating an upper
> range?
> > > > I know it states in 4552 that an upper range had been debated and
> > > > not necessary but I still see an upper added to fab notes.
> > > >
> > > > Regards,
> > > >
> > > > Murray Campbell
> > > > PCB Design Specialist
> > > > [log in to unmask]<mailto:[log in to unmask]>
> > > > [cid:[log in to unmask]]
> > > >
> > > > "This message and/or attachments may include information subject to
> > > > GD Corporate Policies 07-103 and 07-105 and is intended to be
> > > > accessed only by authorized recipients. Use, storage and
> > > > transmission are governed by General Dynamics and its policies.
> > > > Contractual restrictions apply to third parties. Recipients should
> > > > refer to the policies or contract to determine proper handling.
> > > > Unauthorized review, use, disclosure or distribution is prohibited.
> > > > If you are not an intended recipient, please contact the sender and
> > > > destroy all copies
> > > of the original message."
> > > >
> > > “This message and/or attachments may include information subject to GD
> > > Corporate Policies 07-103 and 07-105 and is intended to be accessed
> > > only by authorized recipients. Use, storage and transmission are
> > > governed by General Dynamics and its policies. Contractual
> > > restrictions apply to third parties. Recipients should refer to the
> > > policies or contract to determine proper handling. Unauthorized
> > > review, use, disclosure or distribution is prohibited. If you are not
> > > an intended recipient, please contact the sender and destroy all copies
> > of the original message.”
> > >
> >
> >
> > --
> > Denny Fritz
> > Consultant
> > 812 584 2687
> >
>