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March 2007

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From:
Wayne Thayer <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Wayne Thayer <[log in to unmask]>
Date:
Fri, 30 Mar 2007 16:10:51 -0400
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OK, so I'm a yank....

But, either Inge doesn't know how to calculate/measure adhesion, the "proper" adhesion is not the value Inge was led to expect from the material manufacturer, the substrate vendor did not handle the material property, or Inge has not treated the material properly once it got into the sphere of his influence.

I discount the first 'cause I think Inge is a pretty careful guy, and consider the last option also unlikely since properly manufactured LTCC is pretty tough stuff.

My favorite with LTCC is that DuPont used to list the flexural strength in the completely dry state.  Once any moisture gets into it due to ambient humidity, the flexural strength drops by as much as 30%!  So if you use their material in outer space where there is no moisture, their rated flexural strength is quite applicable.  Otherwise, beware!

Also, this week I got nailed by another substrate manufacturer.  This time HTCC package which Hittite uses.  It is QFN, and the package has as much plating on the QFN pads as on the wirebond sites.  WAY TOO MUCH!!  Hittite response to this is that it isn't their problem, since gold embrittlement is the assembly house's concern, not their's.

I agree that "lying" is an offensive and extreme term, and I hereby retract the suggestion.  But perhaps they left out some important information, such as maybe the adhesion when measured on Venus might be great.

Wayne Thayer

>>> [log in to unmask] 3/30/2007 3:48:23 pm >>>
Dear Doctor K.

I have to do with a very respectable German company, and these guys (all
doctors like you) only respond to facts given in a professional tone. If
I gave the littleast signal of not trusting them... we would be out..
With english ditto, I could just call 'John Smith' and say 'John, what
kind of stuff are you sending to us this time! Has your grandmother
baked the thickfilm this time?'..and I would get something crazy back...
and the negotiations would start immediately.  Americans? I don't dare
say anything, too many yanks in this club....he-he.. Seriously,
Americans are outstanding in one aspect...you get a reaction
instantly...but they can be very stubborn and hard to convince they are
wrong. Like their pr...erh  

Have a Nice Weekend all! 

Inge


-----Ursprungligt meddelande-----
Från: TechNet [mailto:[log in to unmask]] För Joyce Koo
Skickat: den 30 mars 2007 15:48
Till: [log in to unmask] 
Ämne: Re: [TN] Cofired gold

Wayne,
adhesion is depend upon the maturaty of the product and process control.
The surface roughness, cleanliness and material compatibility all play a
role.  For example, "black" substrates might have less adhesion due to
its intrinsic material composition.  I would not to call anyone "lying"
until I know more of details (Inge possibly can call them what ever he
wants after spend few thousands of his analytical work...hehehe...He is
a very rich man)...
Best regards,
                        jk my 1.72 cents

abcd 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Wayne Thayer
Sent: Friday, March 30, 2007 5:18 AM
To: [log in to unmask] 
Subject: Re: [TN] Cofired gold


Hi Inge!

I always prefer destruction.  Something about the finality of the job.

Anyway, I think you are probably going in the wrong direction.  If the
deposits are not porous, then the coverage is probably OK, and as Steve
points out, the print process doesn't have a big window for thickness
you can deposit, anyway--certainly not the factor of 3 you are
suggesting you may be thin by.

If you are ball bonding to LTCC, generally the ball goes on the part
you've mounted to it and the stitch goes on the LTCC.  Are you just
doing some kind of qualification test?

LTCC is magical stuff!  It's a miracle that the stuff holds together
during processing at all, especially during the densification phase of
the firing process.  I'd be looking for a chemistry cause for your
trouble, not print thickness.  If the firing environment got just a tad
low in oxygen, other phases of the process may have stolen the oxygen
molecules necessary for the bond between the metal and the dielectric.
That's exactly what happened to me several years ago with a big LTCC
job:  I fired on low temperature copper on one side, and on the other
side the previously fired and well-adhered gold actually fell off!

So it may be that the LTCC manufacturer was lying about the adhesion you
should have, or it may be that the substrate manufacturer messed up the
firing environment slightly.

Wayne

>>> [log in to unmask]  >>>
Ingemar,

Hmmm.  2 microns huh!  Do you think this is a 'direct write' process?
Sounds awful thin for a stencil don't you think?

I was using a Sonix acoustic microscope.  With a 200+ MHz transducer
[think it was 280 MHz] I could reasonably well pick out the outline of
major circuitry features on the underside of a flip chip, if I had it
gated properly.  

Seeing internal traces within an LTCC body was always dependent upon how
many internal ground planes and RF shields were placed inside the body
as well.  Vias above the target region were always bad news.  You are on
the surface.  You may have a chance, but am not so sure you will be able
to differentiate the top and bottom surface of the conductor when it is
that thin.  Definitely go for the reflected, high-frequency image.

Give the challenge to a really good acoustic microscope guy with a good
machine and decent software  :-)

Steve

-----Original Message-----
From: Hfjord [mailto:[log in to unmask]] 
Sent: Thursday, March 29, 2007 12:34 PM
To: 'TechNet E-Mail Forum'; Creswick, Steven
Subject: SV: [TN] Cofired gold

24 layer stack with cofired AuAg top. Lifts at ball bond pull tests,
insufficient adhesion, I would say. Should take 4,000 psi. Smashed ball
approx. 2 mil diameter. If the gold lifts at 10 grams, then you are >
one magnitude below 4,000 psi. SEM'd edges of lifted lines= 2
micrometers thick. Paste maker recommends >7 micrometers as fired.
Substrate maker denies, that's why I'm asking for method to check all
incoming parts without destruction of the gold.

Abcd recommended confocal laser, don't think that will work. VHF
transducer, not bad idea! Good. Will test that next week. Thanks. 

Inge

-----Ursprungligt meddelande-----
Från: TechNet [mailto:[log in to unmask]] För Creswick, Steven
Skickat: den 29 mars 2007 16:14
Till: [log in to unmask] 
Ämne: Re: [TN] Cofired gold

Ingemar,

Are you speaking of a standard, single print of gold which has been
co-fired into the body of the part, or possibly of a stack of inks which
has been co-fired in at one time?  

XRF comes to mind, but it will require special 'standards', and the prep
of the standards would result in the destruction of a sample of parts to
construct them ... and even then I am not sure how successful you will
be.

It sounds as though a simple profilometer won't get you what you desire
- especially since the bulk of the conductor is below the surface.  I
occasionally did internal inspection of LTCC parts back in the olden
days - but that was looking more for omissions and commissions.

I believe that acoustically, with a very high frequencurface of the
conductor.
The margin of error [due to surface imperfections] may be quite large,
however.  

Can you get them to tell you what their stencil thickness was and based
on solids content have some idea what you may have ended up with?

Will ponder further

Steve
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Hernefjord Ingemar
Sent: Thursday, March 29, 2007 9:39 AM
To: [log in to unmask] 
Subject: [TN] Cofired gold

 
Trikeman or other gnu,

Anyone know of a non destructive method to check cofired topgold
thickness (Au over LTCC)?

Inge



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