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August 2008

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From:
Mike Fenner <[log in to unmask]>
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Date:
Fri, 15 Aug 2008 17:27:11 +0100
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Well I think it looks like what we would call it "graping"  - incomplete
coalescence. A cause is powder oxidation, but it doesn't have to be as
supplied. Could be the solder is oxidizing on reflow through flux
exhaustion. So the fix is profile or a better flux activator.


Regards 

Mike

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Friday, August 15, 2008 1:07 PM
To: [log in to unmask]
Subject: Re: [TN] NiAu Specification for Al Wedge Wire Bonding

Mornin' Inge and Everybody!

I have Inge's bony fish hanging on the wall at:

http://stevezeva.homestead.com/files/troubleshootingfishbone.jpg

I have no experience at all with wire bonding, but after looking at the
diagram, I have a question; is one of the bones under "visual inspect" from
a Tiger Woods fishbone? Hmmmm...

I heard a new term yesterday. It's called "snotballs". We were building an
assembly using SAC305 paste on a ENIG finished PCB. Loaded up a profile that
after plotting, was within all time and temperature parameters that the
solderpaste vendor recommends. After reflow the joints looked like this:

http://stevezeva.homestead.com/files/Snotballs.jpg

Of course we were very surprised at the appearance, solderballs all over the
surface of the fillets. We couldn't figure out what was wrong. After
cleaning, all the balls went away and the joints looked fine. A phone call
was made to our paste vendor, and they asked for the lot number of our
paste.
Some tests were done from the lot of paste that was shipped to us and it was
determined to be a bad lot of paste, we're getting new paste tommorrow. They
told us that the appearance was something they called; "snotballs", and was
probably due to badly oxidized powder. There wasn't a reason given of how
this happened. The paste was made last month. I'm just sharing this image so
that if you see something like this, it will give a clue that the paste is
probably bad.

Steve
  

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Hernefjord Ingemar
Sent: Friday, August 15, 2008 3:05 AM
To: [log in to unmask]
Subject: Re: [TN] NiAu Specification for Al Wedge Wire Bonding

Arnoud et netters,

I've finally found the troubleshooting fishbone for wirebonding. I will ask
Dr Gregory about presenting it on the Zevawall. Don't feel miserable when
you see it...wire bonding use to work without any of the fishbone problems.
Keep the bone, care not to loose it, worthful for production people.

Inge




-----Original Message-----
From: Hernefjord Ingemar
Sent: den 13 augusti 2008 13:12
To: 'TechNet E-Mail Forum'
Subject: RE: [TN] NiAu Specification for Al Wedge Wire Bonding

This is not a fishbone, but you can make a bone of it, if you fish...wish

Wire bonding trouble shooting list:

1. Wrong loop height
2. Improper wire diameter
3. Wire elongation not adapted to object.
4. Wire alloy (doping)
5. Wire age (some wires have limited shelf life) 6. Bonding tool radius 7.
Bonding tool face polish type 8. Bonding tool, build-up of debris in chamfer
and on face 9. Tool vibration amplitude and/or frequency inadequate 10.Bond
force not adequate 11.Bond time not adequate, frequency swing not correct
12.Microscopic damage on wire caused by burrs in the tool 13.Intermetallic
growth between wire and pad metallisation
   (about 10 compounds known, some of which very brittle) 14.Impurities on
or in the bond pads, either they are thickfilm or PWB 15.Inadequate
metallisation thickness vs. dielectric thickness 16.The ultrasonic  energy
causes delamination of bond pad metallisation 17.The wire vibrates too much
in the tool, wire gets microcracks and heel damage 18.The deformation of the
wedge/ball is not sufficient, or is overdone.
19.Insufficient number of microwelds
20.Outgassing of polymers or other stuff, which can cause bond lift or bad
bond yield 21.The bond pad micro structure (asperity)is too rough
22.Diffusion of metals or other stuff, which can change the characteristic.
23.Kirkendall voids, which makes bonds brittle and weak.
24.Maximum current exceeded in bond wire, can cause electro migration
25.Thermal moves that causes bond weakening through defects in the
crystalografic structure 26.Hydrogen bubbles in the metallisation.
27.Presence of halogens in the ambient atmosphere can reduce bond yield
28.Cratering in semiconductor bond pads, too far gone and the wire bond will
lift.
29.Fluorocarbons, chlorides or other residues from the semiconductor process
will disturb the bond process 30.The ultrasonic energy is not correctly
'grounded'(insufficient clamping)
   Especially important for large boards 31.Some wires or PWBs or substrates
should be stored in dry nitrogen
   until the day of wire bonding.
32.So called 'lubricants' may inhibit bond success, e.g. finger prints
33.Contaminations, from the machinery in automatic lines, can contaminate.
34.The superficial surface of Thickfilm gold or silver/palladium pads
contain too much of Si, Bi, or Cd 35.Corroded metallisation of bond pads.
36.Oxides on bond pads
37.Microscopic amounts of water (temporarily), from inadequate storage
38.Microscopic amounts of water from humid ambient

The list is from one of my technical reports, there may be something
missing...

Inge






-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Hernefjord Ingemar
Sent: den 11 augusti 2008 14:05
To: [log in to unmask]
Subject: Re: [TN] NiAu Specification for Al Wedge Wire Bonding

Arnaud et TNetters,

I've not found the wirebonding fishbone, it's so tiny that my cats may have
eaten it all. How ever however, another fishbone may serve some of you, I'll
send it to Dr Gregory , and well packaged so that the custom people don't
feel the smell.

Ineg




-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of arnaud grivon
Sent: den 15 mars 2007 14:51
To: [log in to unmask]
Subject: Re: [TN] NiAu Specification for Al Wedge Wire Bonding

Thanks for the cake, but coming back to the initial question, is there any
standardisation or good practices for the NiAu plating used for Al wedge
bonding?

Best regards,

A. Grivon

Hernefjord Ingemar a écrit :
> Arnoud,
>
> There is a lot to say, I send a good cake to start with ( 4Meg offline).
> If any further questions, send smoke signal. Trikeman is guru.
> Inge
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of arnaud grivon
> Sent: den 14 mars 2007 16:01
> To: [log in to unmask]
> Subject: [TN] NiAu Specification for Al Wedge Wire Bonding
>
> Hello TechNet,
>
> A question for wire bonding gurus (and I know there are some).
> What are the NiAu specifications adapted for Al wedge wire bonding?
> Ni & Au thicknesses, electrolytic or electroless, roughness, 
> hardness....
> Are there some normalized documents covering these aspects (IPC, 
> MIL...)?
> Thanks in advance.
>
> Best regards,
>
> A. Grivon
>
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