Ingemar
I thought you said you were working with heavy wire? 500uM, now
thats heavy! OK, assuming you accept that 100uM is heavy wire, you
should have little problem bonding onto chemical Ni (I guess you take
chemical to mean electroless?) We currently auto bond onto
electroless Ni-P under Au. Admittedly, we use an OE machine, and 8mil
wire (200uM) but it works fine, and foot lifts are extremely rare.
You are right in that the high %P can lead to problems due to
hardness, but using a Au layer can give its own problems. "In
theory", a well controlled process does not need the protection of Au
(and personally I try and keep the Au of any bond pads where ever
possible)
If you are experiencing a lot of foot lifts at bonding, are they
1st or 2nd bond?, also, look closely at the bond site, and check that
you are scrubbing through the Au, it can act as a lubricant and
actually inhibit bonding .
If the foot lifts occur after heat treatment, make sure that you
are forming the Al-Ni intermetallics and not the Al-Au, if the Au is
too thick, and the total bonding energy is low, you may just give
Al-Au bonding, which will decrease in strength over time at elevated
temps (due to consumption of the Au layer, and small diffusion at the
Al-Ni interface after that)
You say that Delvotec perform reference bonding on galvanic Ni, is
it a comparable plating to what you are trying in production? could
be its 10 micron thick and nice and soft, could be they are bonding to
the Al substrate, and leading you up a blind alley.(sorry any Delvotec
reps listening) From experience I have always found that an
electroless 4-6micron mid phos layer is fine, with or without Au, this
has been on both FR4 and ceramic based substrates, with an OE machine
for 5N wire 6-500uM diameter.
More detail on the nature of the problem may help, but good luck
what ever way you go!
Roger
Roger Massey
Materials Technologist
Motorola AIEG
Stotfold - UK
email [log in to unmask]
______________________________ Reply Separator _________________________________
Subject: [TN] Heavy wire Al-bonding on FR4
Author: "TechNet E-Mail Forum." <[log in to unmask]> at #email
Date: 15/04/99 17:52
Hi, all 1577 brains (most of them in UK?).
What a noise this will cause, and hopefully one or two answers will bang
into my briefcase.
Now, we bond 100um Al on Cu/Ni/Pd/Au or on Cu/Ni/Au. Different bath
suppliers, different makers. Different schools. Some say 10-12% P will
cause a too hard Nickel, and there will be problems, bond lifts, which
we also get. Delvotec (bond machine maker, good one)make all their ref.
bonding on galvanic nickelplated aluminium plates, and it works fine.
So, electrolytic and pure Nickel is wanted, but the board suppliers
don't love that, because they have to connect every single bond pad on
the FR4 board, on which the rest of pads are made for ordinary SMT
soldering. Anyone who has autobonded on chemnickel (plus Pd/Au or only
Au)? And are you then satisfied?
Ingemar Hernefjord
Ericsson Microwave Systems
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