We plate tin-lead over nickel regularly, either immediately or after
  another layer of resist.  We're running a Watts bath (nickel chloride,
  nickel sulfate, boric acid) rather than sulfamate.  The activation of the
  nickel surface before the tin-lead plating is critical.  If the nickel
  plate has been dried, there's an initial PC-455 bath to clean the
  surface, then the steps are water rinse, 40% hydrochloric etch, rinse,
  10% fluoboric etch, rinse, tin-lead plating.  Once started from nickel to
  tin-lead, the timings are tightly controlled, certainly no long dwells in
  the rinses or etches.

  Steve Axdal
  [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--------------------------

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