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TechNet E-Mail Forum <[log in to unmask]>, Inge <[log in to unmask]>
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Tue, 19 Aug 2008 10:44:38 -0700
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Trikeman,

Y-O-U  A-R-E  A...A...A...hmmm....A   D-O-U-N-U-T-!!!

That was the best I could find to praise you.  Excellent. I buy every line. 
Feel intuitively that your magic rod is working as always.  Yup, have Al 
wedge, will try it. As you say, one lift is one too much. The customer of 
this laser optic device is worried. I don't know what they use it for, but 
reliability is no1, they pay for that.

'Cat-eye'...good word for the phenomenon. Just now we rather call it 
'Cat-shit'.  Tomorrow, I'll sit down with the customer and go through what 
you recommend. I will start with showing a photo taken from the sky from 
your trike and ask him to contribute with a little bag of sheckels for your 
petrol consumtion..he-he.

Now, besides joking, I bow and say thanks a lot. Hope I can do something for 
you too in du time.

Inge



----- Original Message ----- 
From: "Creswick, Steven" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Tuesday, August 19, 2008 9:57 AM
Subject: Re: [TN] Wire bonding gurus ohoy!


Ingemar,

I know that you have gone home for the evening, but this will be there in 
the morning for you to ponder on.



It's my humble opinion that the 'cats-eye' pattern which you see is related 
to the dominance of U/S energy in the North-South direction of the 
transducer.  It may sound counter-intuitive, but I believe you will find the 
'cats-eye' runs East-West [perpendicular to the dominant mode of oscillation 
of the capillary] - at least that is the way it is on my machines.

I have seen this before in GaAs, InGaN, etc - but usually it is also tied in 
with cratering!  Usually putting too much energy into the crystal ... or in 
the case of Si, just putting too much energy into the bond.

With the exception of a small metallization lift in the upper right tip if 
the 'iris', your metallization appears to be intact.  It appears that the 
bond seriously attempted to adhere.


A couple things that I have experienced with chrome-gold metallizations -

- actually a chrome-gold alloy, being very hard and almost impossible to 
thermosonic gold bond to.  i.e. - you are screwed !! Big time!  Consider a 
switch to aluminum wedge bonding, if you can

- gold layer not exhibiting good adhesion to the chrome layer, and comes off 
during bonding leaving a nice little hole down to the chrome layer.  Be 
loving.  Be gentle.  Should bond like a dream if you can get enough bonded 
area to meet pull strengths.  Increase bonding temp??  Again, can you wedge 
bond?

Neither of the above would seem to apply to your part, however.



I typically run with a 90° inner chamfer and an 8° face angle.  The face 
angle predominantly being dictated by the requirements of the second bond 
surface - the softer the surface, the greater is my face angle.  Not feeling 
that the face angle comes into first bond parameters much other than by 
bond-foot length.

I believe the 120° IC would provide a greater downward vector of 
force/energy, but have not been running with that due to fear of ball 
capture issues during bonding.  Read as the 90° works fine, so am not going 
to rock the boat.

I extensively use an SPT - Small Precision Tools UTS-51KJ-CM-1/16-16mm 
15MTA - an 8° face angle, 90°IC, with 50µm hole.  Am bonding 37.5µm wire on 
100µm square pads 'til the cows come home'.  When dealing with a lot of 
LEDs, used a similar capillary with the same wire but on 75µm square pads. 
Ran like a champ!  Not an easy challenge to put down wire that large on 
those smallish pads without cratering/lifting/etc.


I'm sure you have tried all the 'normal' stuff like:

- plasma cleaning to freshen up the surface.

- Compared old vs new lots.

- Contemplated running across the EDS to check for a preponderance of chrome 
on the surface - although 2500A of Au may not do a good job of blocking out 
the rest of the chrome from the signal electrons either.

- Verify heat column temps and clamping.

- verify they are not actually over-bonding [visual observation of bonds]


Ingemar, I am at a loss to think of anything else to jot down at the moment. 
Hoping that sharing bonding tool info helps to some degree.  You've not 
really said if this is a new lot of die, or there was some other upstream 
process change, etc. that you are investigating ....so I am still shooting 
in the dark somewhat.  You are probably like me in that 'many' bond lifts is 
something like 1-2 out of a hundred or more  :-)  One is TOO many!

Steve



-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory
Sent: Monday, August 18, 2008 8:30 AM
To: [log in to unmask]
Subject: Re: [TN] Wire bonding gurus ohoy!

Mornin' Inge!

Got your picture posted, but that's all the help I can offer...I know
nothing about wire bonding.

Your picture is here:

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

Steve

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Hernefjord Ingemar
Sent: Monday, August 18, 2008 4:13 AM
To: [log in to unmask]
Subject: [TN] Wire bonding gurus ohoy!


 Hi all,

will send a picture to Steve for getting help.
Thermosonic 25um gold balls don't stick to the thinfilm gold on a optic
chip.
2,500A Au over 400A Cr. Bad yield, many balls lift. No contaminations
found.
Despite I have the good fishbone, I can't find out why the odd pattern
under lifted bals.
A guess is that the capillary have to steep chamfer angle, so that the
U/S mechanical energy becomes concentrated in the middle. Anyone with
similar experience?

Inge

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