Carey, people will get tired, this conversation a bit from PWBs, but as you are professional and kind, Carey, I feel that the chat may be accepted with some  more Bytes. Comments, see below. / Ingemar


Carey's Internet course in "dirt analysis and removal" on bond pads. Cont'd:
--------------------------------------------------------------------------
Ingemar
Your improvement by sputtering Au onto your pads indicates your surface was
dirty.  Presumably, there was a plasma clean before your deposition but, if
not, you cleaned it somehow and its not important to discussion.  You then
had a clean, oxide-free (again, Au doesn't form an oxide) surface that
allowed full contact with the wire.  This supports wire bonding is not deep,
but along the interface.

RE: How deep do you think,speaking about 25um gold wire and U/S ball bonding?




Auger analysis (a process that shoots in electrons and looks at core
electrons in atoms) would NOT have helped you because you always expect
impurities on the surface, and Auger cannot distinguish chemistry (for the
most part).

RE: at least you get an idea of what elements you have. An extremly high Carbon peak could reinforce our assumtions about epoxy contaminations, couldn't it?



It does sound like your group needs the regular input of a thin film
metallurgist/materials scientist.  I suggest you connect up with someone in
the ericsson company arena (I'm thinking on the semiconductor side since PWB
shops are not there yet) on a regular basis.  Then one can design a series
of experiments to address issues proactively (it never works in a panic,
reactive mode).  Unfortunately, board shops do not have the mentality to do
this, and the cost is high.  But soon, it will be cost-effective as board
prices climb higher as does volume/shop.

RE: I have been speaking with our wafer fab, but they had no further proposals how to indicate "dirty" gold. I said they  should because they put gold on backside of the wafers. But realized that.... backside....not so interesting for semi people.


Good luck
Carey

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