TECHNET Archives

May 2013

TechNet@IPC.ORG

Options: Use Monospaced Font
Show Text Part by Default
Show All Mail Headers

Message: [<< First] [< Prev] [Next >] [Last >>]
Topic: [<< First] [< Prev] [Next >] [Last >>]
Author: [<< First] [< Prev] [Next >] [Last >>]

Print Reply
Subject:
From:
Bev Christian <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Bev Christian <[log in to unmask]>
Date:
Wed, 29 May 2013 20:16:59 -0400
Content-Type:
text/plain
Parts/Attachments:
text/plain (463 lines)
Inge,
What Mike and I are saying is that a gold atom IS a gold molecule.  I don't
like it, but that is how the term is being used.
Bev

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Inge Hernefjord
Sent: Wednesday, May 29, 2013 11:51 AM
To: [log in to unmask]
Subject: Re: [TN] Gold Removal

Mike,

I admire your patience. I absolutely agree with all that you say, classical
school stuff. I still can't see why gold should appear as molecules in a
metal interdiffusion process. I have read lots of reports about gold
migration and diffusion in gold plated semiconductors,  like MESFET, HBT.
Written by TI or NG or others, and gold is never mentioned as molecules in
the mentioned processes. Well, I stop here, let's leave the topic, I risc
fool myself.

Inge


On 29 May 2013 13:27, Mike Fenner <[log in to unmask]> wrote:

> Inge
> Try it this way
> A molecule is the smallest chemically stable form a substance can exist
in.
> The term is usually used to mean combinations of different elements but
can
> also be used to describe for example an oxygen molecule which is just a
> pair
> of oxygen atoms. A single oxygen atom is not chemically stable and will
> react with anything handy if it can, or pair up with another oxygen atom
if
> it can't. Oxygen is diatomic.
> Neon on the other hand doesn't do this so the smallest chemically stable
> unit of neon is one atom; it's monatomic in other words. By the definition
> above a neon atom is a molecule, but it wouldn't usually be thought of in
> that way.
> The problem of understanding chemical terms is that though there are laws
> of
> chemistry not all chemicals completely obey they them. The Laws can be
more
> like Rules. Things can be a bit fuzzy at the margins. At the same time
> chemical terms have entered every day use and have grown fuzzy too. So
> which
> term to describe what is also fuzzy, there can be more than one. Chemists
> know what they mean because they know the context and there are
> linguistic/social conventions as well as scientific on word use. This can
> be
> a bit puzzling for non chemists, especially engineers not familiar with
> these conventions and who like everything neat and tidy.
> (Comment: This is partially why we get into such back and forth on stuff
> like defining fluxes and how they work.)
>
> Nearly all elements are chemically active. They therefore chemically react
> to form molecules. Some of these molecules are very simple: carbon dioxide
> is CO2 and water is H2O. Some of them are more complex. One of my
favourite
> molecules is C2H6O which is more normally written C2H5OH or CH2CH3OH which
> reflect how the atoms are arranged. Its everyday name is of course ethyl
> alcohol, more formally known as ethanol. The chemistry of life is very
> complicated and some molecules are very large indeed - DNA for example.
The
> chemistry of life was originally called organic chemistry, the chemistry
of
> organisms; because carbon is intrinsic in organisms it also meant the
> chemistry of carbon.  The chemical industry has now synthesised some "life
> chemicals" ethanol being one, plus thousands of new chemicals and
continues
> to do so. So organic chemistry now is usually understood to refer to that
> part of chemistry. This leaves inorganic to describe the rest of chemistry
> not described by any of the terms evolved above.
>
> Some elements don't react at all they are inert, argon neon etc. they are
> loners. Monatomic.
> Gold is pretty well nearly inert, so stays monatomic, but under certain
> circumstances can be made to react. So it's in one the fuzzy zones
> mentioned
> above.
> When Brian comes in he may or may not feel motivated to simplify/correct
> this explanation, meanwhile I don't know if this helps or not, but as I've
> typed it I'm sending it :)
>
>
>
>
> Mike
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Inge Hernefjord
> Sent: Wednesday, May 29, 2013 7:06 AM
> To: [log in to unmask]
> Subject: Re: [TN] Gold Removal
>
> Bev,
>
> Alright. Remember that I am a fossil. We talked 'atoms'  for Solid State
> Technology and Metallurgy  in general. And molecules belonged to organic
> chemistry. Still I don't understand why gold should diffuse as gold atom
> pairs in a gold tin interdiffusion process.  But never mind, there are
more
> important things in daily life...
>
> Inge
>
>
> On 29 May 2013 02:35, Bev Christian <[log in to unmask]> wrote:
>
> > Inge,
> > Technically Richard is correct, see first meaning below.
> >
> > Random House, Dictionary.com & Funk and Wagnalls Encyclo.
> > - the smallest physical unit of an element or compound, consisting of
one
> > or
> > more like atoms in an element and two or more different atoms in a
> > compound.
> >
> > - any very small particle.
> >
> > Personally I prefer this one below, so for many elements I look at them
> as
> > monatomic and would only speak of them as "atoms", not molecules.  I
> think
> > this is where you are coming from.
> >
> > Collins English Dictionary
> > - the simplest unit of a chemical compound that can exist, consisting of
> > two
> > or more atoms held together by chemical bonds
> >
> > Regards,
> > Bev
> >
> > -----Original Message-----
> > From: TechNet [mailto:[log in to unmask]] On Behalf Of Inge Hernefjord
> > Sent: Tuesday, May 28, 2013 5:03 PM
> > To: [log in to unmask]
> > Subject: Re: [TN] Gold Removal
> >
> > What is 'Gold molecules' ?
> > I should know, but need some updating..
> > Inge
> >
> >
> > On 9 May 2013 21:26, Stadem, Richard D. <[log in to unmask]>
> wrote:
> >
> > > As an engineer, I understand metal rulers quite well. I work with
goops
> > > and glues also, and I agree that you have to have somewhat of a
> > left-minded
> > > brain to understand that part. I agree it is better left to people
like
> > > Doug and Dewey.
> > >
> > > From: [log in to unmask] [mailto:
> [log in to unmask]]
> > > Sent: Thursday, May 09, 2013 11:37 AM
> > > To: Stadem, Richard D.
> > > Cc: TechNet E-Mail Forum
> > > Subject: RE: [TN] Gold Removal
> > >
> > > Hi Dean - yes, the 1% concern is when you have a "segregated zone"
> where
> > > the gold is not uniformly distributed within the solder joint. The
JSTD
> > 001
> > > Handbook goes into fairly good depth on soldering process constraints
> > that
> > > deal with the gold distribution. Using your 1% rule would keep you out
> of
> > > trouble without question.
> > >
> > > Good discussion - better than that "goops and glues" stuff Doug was
> > asking
> > > about.  Metals rule  (Ok, please don't shoot me for that, its directed
> to
> > > Doug and Dewey).
> > >
> > > Dave
> > >
> > >
> > >
> > > From:        "Stadem, Richard D." <[log in to unmask]<mailto:
> > > [log in to unmask]>>
> > > To:        "[log in to unmask]<mailto:
> > > [log in to unmask]>" <[log in to unmask]<mailto:
> > > [log in to unmask]>>, "TechNet E-Mail Forum" <
> [log in to unmask]
> > > <mailto:[log in to unmask]>>
> > > Date:        05/09/2013 09:56 AM
> > > Subject:        RE: [TN] Gold Removal
> > > ________________________________
> > >
> > >
> > >
> > > Thank you, Dave. That is greatly appreciated! And now:
> > > The 3-5% gold content is an industry-accepted ballpark figure. Gold
> > > embrittlement can also be seen with gold percentage as little as 1%.
> Much
> > > also depends on the base metal that the SJ is formed with, and the
> > > geometrical shape of the solder joint can also contribute heavily to
> the
> > > embrittlement level. For example, gold plated wire cups are notorious
> for
> > > embrittlement if not pre-tinned properly. So are gold plated
terminals,
> > > certain types of IC and hybrid leads, and a few other configurations.
> >  For
> > > very high reliability applications, it is very very important to
> monitor
> > > the gold (and other impurity levels).
> > >
> > > From my personal experience, a limit of 1% gold works 99.99999999999%
> of
> > > the time. Several times in my career I have seen termination finishes
> > that
> > > met the 3-5% limit fail in the field later. Believe me, you do not
want
> > > that to happen to you!
> > >
> > > And when working with gold-plated parts, especially SMT connectors, it
> is
> > > always a good idea to perform XrF periodically at receiving inspection
> to
> > > make sure that the gold thickness is actually remaining within the
> > > component SCD limits.
> > >
> > > From: [log in to unmask]<mailto:[log in to unmask]
> >
> > > [mailto:[log in to unmask]]
> > > Sent: Thursday, May 09, 2013 9:13 AM
> > > To: TechNet E-Mail Forum; Stadem, Richard D.
> > > Subject: Re: [TN] Gold Removal
> > >
> > > Hi Dean - you may not be a metallurgist but you must have stayed at a
> > > Holiday Inn recently. Very very good process details. Let me change
> your
> > > last paragraph just a bit.
> > >
> > > Gold and tin will form a intermetallic compound (IMC) - AuSn4 - when
> the
> > > solder joint composition contains 3-5 weight % gold. This IMC is very
> > > brittle and will crack during vibration, drop shock or thermal cycling
> > > causing the solder joint to degrade and fail (not a porosity issue).
> The
> > > good thing is that gold diffuses into solder at a rate of 100
> microinches
> > > per second so when the procedures Dean listed are followed, there is
> very
> > > little chance of having a gold embrittlement issue. The process goal
is
> > to
> > > not allow the gold content in the solder to exceed the 3-5% range.
> The
> > > IPC JSTD 001 Handbook and the IPC AJ 820A Handbook have a very good
> > section
> > > on this issue.
> > >
> > > Dave
> > >
> > >
> > >
> > > From:        "Stadem, Richard D." <[log in to unmask]<mailto:
> > > [log in to unmask]>>
> > > To:        <[log in to unmask]<mailto:[log in to unmask]>>
> > > Date:        05/09/2013 08:30 AM
> > > Subject:        Re: [TN] Gold Removal
> > > Sent by:        TechNet <[log in to unmask]<mailto:[log in to unmask]>>
> > >
> > > ________________________________
> > >
> > >
> > >
> > >
> > > Good question, Bob.
> > > Gold does not "melt" at soldering temperatures. A dissolution process
> > > takes place, and because gold plating on component leads is so thin,
> the
> > > dissolution is typically enough to absorb all of the gold into the
> solder
> > > bath upon contact with the molten solder. This is also how a solder
> joint
> > > is formed with copper and certain other metals. Copper, gold, silver,
> and
> > > nickel do not melt at normal solder temperatures, a small amount is
> > > dissolved to form the bond with the solder, called the intermetallic
> > > formation.
> > >
> > > A double tinning method utilizes the first tin pot to dissolve and
> absorb
> > > the gold into the molten solder, and the second pot is required to
> ensure
> > > the remaining solder is relatively free of gold (the first pot has
gold
> > > levels increasing over time as the tinning is performed, so the second
> > pot
> > > is used to make sure no gold remains). The dual pot method is used
> where
> > > only a small amount of solder is used for tinning, and is thus more
> > easily
> > > filled with unwanted "impurities" (other alloys and elements other
than
> > > Sn63Pb37 or whatever the desired alloy is). The dynamic wave is simply
> > > another option for obtaining the same results, where a larger volume
of
> > > solder is pumped to provide a laminar flow that will ensure the gold
is
> > > removed and replaced with the target alloy, Sn63Pb37 as an example.
> > Because
> > > of the larger solder volume in the dynamic wave method, the gold
> content
> > is
> > > diluted such that it does not go above the limits listed in J-STD-006.
> > >
> > > When using a double pot method, the gold content must be monitored in
> > both
> > > pots. This is done with a regular pot analysis, and the data is used
to
> > > determine the frequency of solder replenishment to dilute the gold and
> > > other alloys to an acceptable level. The solder test is relatively
> > > inexpensive and can be performed by solder companies such as Alpha,
> > Kester,
> > > etc. With the laminar flow method, you still need to test at regular
> > > intervals, but because of the larger volume of solder it takes longer
> for
> > > the gold and other impurities to go above the specified limits.
> > >
> > > Tinning data should be kept to determine the frequency of sampling for
> > > test, as well as how often the solder should be refreshed with new
> solder
> > > to dilute the impurities to an acceptable level. A simple tinning log
> is
> > > valuable in determining the history (number of components tinned, what
> > > type, and when) to quantify the amount of tinning over time in order
to
> > > help determine the safe frequency for adding solder that will ensure
> the
> > > alloy will remain within spec, the spec being J-STD-006, including
> > Appendix
> > > A and B, which list the allowable levels of "impurities" (it's hard to
> > > consider how gold and silver can be considered "impurities", but it's
> all
> > > relevant to the goal of Sn63Pb37 for leaded solder, and nothing else).
> > > J-STD-006 also lists the test methods used to determine the
impurities.
> > >
> > > The concern with having gold levels above the limits in the J-Standard
> is
> > > that gold in the solder joint will nucleate through the hardened
solder
> > > joint towards the junction of the component lead and the solder,
and/or
> > the
> > > pad and the solder (the intermetallic junction). Gold wants to return
> to
> > > this intermetallic boundary, like many other elements seeking
> > equilibrium.
> > > So the gold molecules will actually travel through the solder joint
> over
> > > time (nucleation), leaving behind a more porous solder joint, which is
> > > called embrittlement, which leads to solder joint fractures and
> > potentially
> > > catastrophic electrical failure.
> > >
> > > I am not a metallurgist by training, so this explanation may be
> somewhat
> > > crude to those who are, but I think it will serve the purpose of
> > > explanation. For all of you metallurgists out there, feel free to
> expand
> > on
> > > this or correct me.
> > >
> > > Hope this helps you,
> > > R. Dean Stadem
> > >
> > >
> > > -----Original Message-----
> > > From: TechNet [mailto:[log in to unmask]] On Behalf Of Robert DeQuattro
> > > Sent: Thursday, May 09, 2013 7:28 AM
> > > To: [log in to unmask]<mailto:[log in to unmask]>
> > > Subject: [TN] Gold Removal
> > >
> > > Hello Fellow Technetter's,
> > >
> > > I have a question on J-Std-001E 4.5.1 Gold removal which states a
> double
> > > tinning process  or dynamic solder wave may be used.  Can any of you
> > > describe this process.  How is the gold actually removed?  Or is it
> just
> > > being tinned?  Gold melts at over 1000 C so I am a little confused.
> > >
> > > Thanks,
> > >
> > > Bob
> > >
> > > ______________________________________________________________________
> > > This email has been scanned by the Symantec Email Security.cloud
> service.
> > > For more information please contact helpdesk at x2960 or
> > [log in to unmask]
> > > <mailto:[log in to unmask]>
> > > ______________________________________________________________________
> > >
> > > ______________________________________________________________________
> > > This email has been scanned by the Symantec Email Security.cloud
> service.
> > > For more information please contact helpdesk at x2960 or
> > [log in to unmask]
> > > <mailto:[log in to unmask]>
> > > ______________________________________________________________________
> > >
> > >
> > > ______________________________________________________________________
> > > This email has been scanned by the Symantec Email Security.cloud
> service.
> > > For more information please contact helpdesk at x2960 or
> > [log in to unmask]
> > > ______________________________________________________________________
> > >
> >
> >
> > ______________________________________________________________________
> > This email has been scanned by the Symantec Email Security.cloud
service.
> > For more information please contact helpdesk at x2960 or
> [log in to unmask]
> > ______________________________________________________________________
> >
> >
> > ______________________________________________________________________
> > This email has been scanned by the Symantec Email Security.cloud
service.
> > For more information please contact helpdesk at x2960 or
> [log in to unmask]
> > ______________________________________________________________________
> >
>
>
> ______________________________________________________________________
> This email has been scanned by the Symantec Email Security.cloud service.
> For more information please contact helpdesk at x2960 or [log in to unmask]
> ______________________________________________________________________
>
>
>


______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask] 
______________________________________________________________________


______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please contact helpdesk at x2960 or [log in to unmask] 
______________________________________________________________________

ATOM RSS1 RSS2