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March 2007

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Subject:
From:
"Creswick, Steven" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Creswick, Steven
Date:
Thu, 29 Mar 2007 12:57:32 -0400
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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 frequency transducer you
should be able to gate off the top and bottom surface 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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