Hi Julie,

The formation of smut is dependent on both factors -- the presence of palladium
on the copper surface and the presence of certain organic additives in your
plating bath.  If Pd activation is not used or the plating solution is
additive-free or if palladium layer is covered with a dense and thick
electroless copper deposit -- it won't form .  As far as I know the presence of
anode film is not a factor.  My guess is that this smut consists of cuprous and
cupric oxide mixture.  During electrodeposition cupric ion goes through a
cuprous state and under certain conditions may not reduce all the way to the
metallic state.  Some organic additives in your plating bath and chloride ion
may stabilize cuprous by complexing it.  Although the exact smut formation
mechanism is not entirely understood, there are some things you can do to reduce
it.  Please contact me offline if interested.

Eric Yakobson





Julie Dixon <[log in to unmask]> on 03/22/2000 11:38:29 AM

To:   [log in to unmask]
cc:
Subject:  [TN] Low Current Density Smut



Dear Net,

1. Is there a name, we use smut, for the slimy, dark brown-black deposit in
low
current density areas on panels in acid copper plating? It wipes off as a goo
down
to the foil copper.
2. Is it related to DML boards only? Palladium on surface issue?
Or is it related to DML's reaction with the brightner system in the plating
bath?
I've been told it's brightner related, but it never occurs on anything not
DML'd.

 -Cold panels 70 F almost always manifest it.
 - But recently we saw it on 74 F panels plated at 35 asf for the first 5
minutes.
   a. bath had been inactive for 5 days, but continuously filtered, and air
agitation
       had been on for 2 hours prior to plate. Anode film?
   b. design was a horrendous mismatch of copper area. We panelized best we
could
        front side-   1-9"         9-18"     the front 1-9" area smutted.
Other area were ok.
                         10x            1x
                         copper area
        back side-   1-9"         9-18"
                           1x           10x

Any experience with this? We thought we'd shelved this prob. with 98 F rinses
in the
pre plate. Sulfuric dip and plating bath are at the mercy of ambient
conditions, typic
74 F.

Thanks,
Julie

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