Tom:

I've never tried to plate solder over nickel, but nickel does passivate rapidly when exposed to
air.  Back when hand lines were used for plating nickel/gold edge connectors, it was well known
that the nickel plate had to be activated by a dip into 10% to 15% sulfuric acid.  In your case,
I'd recommend attempting to activate the nickel with an acid compatible with your plating bath
(usually fluorboric or sulfonic depending on your bath).  A 2 to 3 minute immersion in the acid
followed by a quick rinse and into the solder bath.  Given that sulfuric is normally supplied at
98% to 96% and the others are considerably weaker, you might have to experiment with the
concentration.

As I recall, the reason for acid activation between nickel and gold plating was removal of the
organics used in the nickel bath as well as the prevention of oxidation.  If the activation step
was inadequate, the gold would plate the tabs, but the end product would fail a tape test.

Don Vischulis
[log in to unmask]

Tom Bresnan wrote:

>      All:
>
>      Is there a preferred nickel I should be trying to plate solder on top
>      of? We're struggling with plating tin lead on top of nickel and it's
>      subsequent reflow after soldermask. Anyone have any suggestions? We're
>      seeing dewetting and I'm wondering how many others out there are
>      trying to do this. We currently use a nickel sulfamate bath, if that
>      has any bearing... I'm not sure of activators and such, but if you
>      think it's important, I'll find them.
>
>      Thanks in advance all...
>
>      Regards
>
>      Tom Bresnan
>      [log in to unmask]
>
>      PS. Please respond direct to me as well as to the forum. I'm presently
>      disconnected from the service.

snip--------------------------

################################################################
TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c
################################################################
To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body:
To subscribe:   SUBSCRIBE TechNet <your full name>
To unsubscribe:   SIGNOFF TechNet 
################################################################
Please visit IPC web site (http://jefry.ipc.org/forum.htm) for additional information.
For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312
################################################################