Uneven electroless nickel plating has been traced in the past to following
factors

1)  Residual tin lead

2)  Overstable electroless bath (normally caused by over adds of replenishments)

3)  Excessive agitation level in the electroless bath

4)  Too low a loading factor in the electroless bath

5)  Poor solder mask development (in processes where Ni/Au is applied after
mask)


In the Technet message, tin is described as the etch resist. We have actually 
used immersion tin as a pretreatment for electroless nickel in the past. It is 
not clear whether incompletely stripped electrolytic tin might lead to 
initiation problems. However, the fact that the uneveness was visible at the 
tin strip stage suggests that the stripping or the tin deposit might be the 
problem.

The effects of traces attached to pads are usually caused by larger areas of 
copper helping to overcome the reluctance of a particular pad to initiate.

Gold thickness is normal on the dull pads, since the immersion gold bath will 
also deposit a similar thickness on bare copper.

Hope this is of some help.

The Shipley Company
John S. Grosso
Director
PWB R&D

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