I agree fully with you!
Have actually encountered situations where multiple [up to ~10] 50
micron wires per pad greatly increased likelihood of cratering and
lifting, whereas one 250 micron aluminum wire did not.
Yes, technically they were not EXACTLY all equal either.
Steve
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Hernefjord Ingemar
Sent: Friday, October 10, 2008 4:26 AM
To: [log in to unmask]
Subject: Re: [TN] Need soldering advice ASAP!
The production manager is hunting me for a solution, quick one. He has
proposed the operators to skip aluminium wire and parallel four 50
micron gold ball wires instead. I'm not happy with that either, because
of the risk of gold/aluminum IMC (purple plague)with high currents and
high temperature. Furthermore, using four wires in parallel does not
mean equality. What do you think?
Inge
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Creswick, Steven
Sent: den 9 oktober 2008 21:33
To: [log in to unmask]
Subject: Re: [TN] Need soldering advice ASAP!
Inge,
Metal buildup in the bonding tool causing bond lifts??
I am of the same mindset as you and Wayne present.
Very confusing
Steve
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Inge
Sent: Thursday, October 09, 2008 3:26 PM
To: [log in to unmask]
Subject: Re: [TN] Need soldering advice ASAP!
I'm surprised. Heavy wire with Al use to be very uncritical. The high
energy density use to push aside all debris and if the metallisation
isn't too
thin, a connection is easily created. And me too, also doubt about
voids.
We have already Xray'd and made bonding attempts on those with voids and
those with few or no voids. Same result. If I speak nicely to Mr
Murphy...
Inge
----- Original Message -----
From: "Thayer, Wayne" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Thursday, October 09, 2008 12:18 PM
Subject: Re: [TN] Need soldering advice ASAP!
I agree that some voids should not present a problem for the aluminum.
A test would be to look for voids on the Xray and then try bonding both
on the void and off of it to see if there is some kind of "drum effect"
going on, but I doubt it.
Wayne
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Inge
Sent: Thursday, October 09, 2008 1:30 PM
To: [log in to unmask]
Subject: Re: [TN] Need soldering advice ASAP!
Already fixed, a glass of my home made wine is already standing on my
desk!
Made on pumkins. English pumkins. American pumkins too bitter.
Bondlifting or do not stick.
No, dice or not jumping off..
Everything is checked: wire, wedge, parameters, clamps are new made,
workholder polished to best planarity, preforms are controlled etc. We
get same bad result on the other heavy wire bonders.
Frit..oufff...no-no-no..mixed
Burnish good idea, will try that.
Our feeling is that it must be either the die surface or voids.
Inge
----- Original Message -----
From: "Creswick, Steven" <[log in to unmask]>
To: "TechNet E-Mail Forum" <[log in to unmask]>; "Inge"
<[log in to unmask]>
Sent: Thursday, October 09, 2008 10:09 AM
Subject: RE: [TN] Need soldering advice ASAP!
Inge,
Maybe you've had enough nuts and should switch to a liquid??
Bonds are just not sticking???
Understanding that voiding is not desired, but what leads you to believe
that is the cause of the bonding problem? Die coming up?
Are you absolutely sure nothing has changed in the clamping of
substrate/package and that the bonding tool is firmly clamped in the
transducer?
Cd is a new one to me too...
I've had some of our thick film golds outgas substantially, although the
vacuum reflow helped a great deal.
If it is a mixed bonded gold, it is possible that you have a slightly
glass-rich surface. Some are more sensitive to furnace atmosphere
contaminates as well.
Doubt you are using a fritted gold.
Burnish before reflow if a de-wetting issue?
Steve
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Inge
Sent: Thursday, October 09, 2008 12:53 PM
To: [log in to unmask]
Subject: Re: [TN] Need soldering advice ASAP!
50%
Inge
I have to get an advice soon, because I have consumed a 250 gram box of
cashew nuts while searching for tips , and reach for another
one...burp..
----- Original Message -----
From: "Creswick, Steven" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Thursday, October 09, 2008 9:41 AM
Subject: Re: [TN] Need soldering advice ASAP!
Are the voids so huge as to PREVENT good mechanical clamping of the die
for bonding? - sorry
Steve
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Creswick, Steven
Sent: Thursday, October 09, 2008 12:37 PM
To: [log in to unmask]
Subject: Re: [TN] Need soldering advice ASAP!
Ingemar,
Ours used to be CrNiAg backside metallization.
My experience with the resultant AuSnAg alloy that forms is that once it
has reflowed, it virtually is impossible to rework [if you ever wanted
to].
Outgassing of the substrate metallization? Thin film or thick?
Obviously, thick film worse.
Are the voids so huge as to provide good mechanical clamping of the die
for bonding? It would seem to have to be absolutely terrible voiding to
cause that. Is there something else going on, like a flux, or change in
clamping, etc.
Seems like I have bonded some really badly voided parts with out issue
Steve
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Inge
Sent: Thursday, October 09, 2008 12:00 PM
To: [log in to unmask]
Subject: [TN] Need soldering advice ASAP!
Hi all, especially the Indi-man,
We have soldered IRC's power MOSFET (100-250 W) dice for a decade
without problems. They use to be vacuum soldered to a solderable gold
thickfilm
Al2O3 substrate with AuSn 50 micrometer preforms. Now there is a
production stop because of Al heavy wire wedge bonding problems. My
analysis of this case points at the presence of large voids in the
solder joints or maybe partly dewetting (FineFocus is good but the
resolution is not sufficient to make me sure), something the US
mechanical waves don't like. The die backside is plated with something
that I don't recognize: Cadmium over Silver over Nickel. What the heck
is that? Anyone who can figure out if AuSn is the best preforms for that
plating?
Thanks
/Inge
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