>HI JK,
felt that I had to tell you that I'm using your comments. Yes, I'm
sucking and tasting and thinking. Maybe I will be more wise than before.
If something more appears, I will let you know. I use to come back, say
thank you and tell what happened next. But it can take some time. See
you at the end of the fibers./Ingemar


 Dave hit the nail on the head.  The difficulty of wire bond on gold may
have
> many root causes. Here are my 2 cents:
>
> (1) Plating problem.  Plating condition, e.g.current density, PH,
additive
> concentration variation will resulting entrapment of impurities
> (co-deposite),  sometime the Au deposite become porous.  A good
reference
> paper for Au plating is:
>         High-Performance Gold Plating for Microdevices - by A. Gemmler
> et.al. Plating and Surface Finishing, Aug. 1994, p.52
> If your vendor perform the similar analysis as indicated in the paper,
you
> would not have any worry about the wire bonding for a long time (You
will
> notice the change on the "wire bonding yield chart"  if someone
changed job
> on your vendor side. for example, an engineer or QA...or someone
decided to
> go "out sourcing", cut cost to "extend Au bath life", etc...No
kidding!)
>
> (2) Surface contamination and surface diffusion.  Poor coverage at the
edge
> of the gold pads (exposed Cu or Ni) sometime will result Cu/Ni
migrated to
> Au surface under humidity condition.  (surface diffusion is 2 order of
> magnitude high than the bulk diffusion).
> Insufficient final rinse (or delay of the final rinse, e.g. "went for
> lunch") after the plating may cause residue on the gold pad (oxidation
of
> residue...e.g.brownish look Au for KCN based plating).  Good
reference:
>         The Auger Analysis of Contaminants that Influence the
> Thermocompression Bonding of Gold. - by G.E. McGuire et.al, Thin Solid
Films
> Vol. 45, 1977. p. 59
>
> (3) Plasma cleaning does have some draw backs:  You will activated PWB
> surface too.  Plasma clean is a standard cleaning method used for
ceramic
> thin/thick film product prior to wirebond.  The work time after the
clean is
> limited to few hours (depend upon what class of clean room you are
using).
> It is costly to do surface analysis (Auger, SIMS, XPS) to define the
working
> time after plasma clean.  I usually specify on the low side (ASAP=less
than
> 0.5 hr).  UV-Ozone may be faster, but PWB damage have to be assessed
if you
> are using FR4 or polyimide.
>
> (4) Hardness of Au is a quick and cheap way to define high quality Au
(it
> does not tell you much about surface contaminant).  However, it is not
easy
> to do micro hardness (you need special machine!  $$$!).  Particularly,
when
> thickness is on the low side (< 30 micro-inches).
>
> (5) It is difficult to do cost-benefit assessment for plasma
equipment.
> Quality improvement normally take about half a year to show some
measurable
> result.  I face the same issue too.  Please accept my condonlence.
>
>  my 2 cents...Good luck.
> a pupil (jk)
>
> p.s. regarding Au quality, you may want take a look of  "The use of
SIMS to
> investigate wire bonding yield problem on gold contact" by G.R. Mount,
> et.al. MRS Symp. Proc. Vol. 390 Electronic Packaging Material Science
VIII,
> 1995 p.245
> ---------------------------------------------------------------------
> At 07:55 AM 4/21/99 -0700, you wrote:
> >All this back and forth conversation is great regarding how to bond
to Au.
> >Remember the first rule of thumb. GET TO THE ROOT CAUSE!!!!
> >
> >A eraser is simply abrading the surface, removing "crud" but also
removing
> >precious Au that you need for acceptable bonds.  The eraser does not
> >miraculously act as a vacuum but a tool to smear the crud, not remove
it.
> >If it is an organic problem that you have, plasma may work but plasma
will
> >only remove ~200-300 angstroms, not a whole lot being removed.
Plasma also
> >depends on the gas, flow, temp, electrode configuration, chamber
size.  You
> >just can't buy a plasma unit and plug it in.
> >
> >Good Luck and if more help is needed, I can be reached at
> >[log in to unmask]

> >---------------------------------------------------------------------
> > Hi, sorry to get in between. You seem to discuss what is hot also
here
> >at our company to and from. My first question would be: please,
> >gentlemen, what are you from Chuck and pupil? I have got some good
> >advice from Dave at Rockwell,  maybe we have something good to learn
> >from you too. I have tried for one year to buy an american plasma
> >cleaner, but when the economists ask  "what is the payback time" ,
then
> >what can I answer? Oh, my adrenaline...! /Regards
> >
> >                                       Ingemar Hernefjord
> >                                    Ericsson Microwave Systems


>

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