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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