Gabriela Bogdan wrote:
>
> Hello, TechNetters!
> Some questions about electrolessNi/Au plated circuits:
> What is the cause of shadow plating between the pad and the surrounding
> solder mask?
> Is it acceptable by IPC standards for Class2,3 if it extends to 30% of
> the distance between the
> fine pitch lands separated by ~4mil solder mask?
> It seems that the presence of the solder mask near the plating area
> enhances the occurrence of
> the phenomenon.
> Also, we see differences in the appearance of the fine pitch area
> between two different manufacturers.
> One of them gives us very clearly defined pads without any shadowing ,
> the other-shadow plating
> along the long edges of the pads, for the same artwork.
> We are concerned about violating the IPC requirements ,about the
> necessity of solder mask
> between the pads with less than 20mil pitch and about shorts after
> reflow soldering.
> Please answer me as soon as possible.
> Thank you in advance for your help,
> Gaby
>
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> ################################################################Dear Gaby,
A few potential causes of the problem you described can be traced to
solder mask bleed onto the pads or soldermask leaching onto the pads
during the electroless nickel plating process. The chemistry and plating
conditions in the nickel are fairly aggressive.
It is also possible that the electroless nickel plating solution is being
operated out of spec with respect to catalyst concentration, accelerator,
proper rinsing and nickel deposition rates.

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