I have found all the factors listed in Mr. Grosso's message to be a 
     cause of uneven plating  in our electroless nickel/immersion gold 
     plating line as well.  I'd like to add a couple more:
     
     --  incomplete removal of microetch residues before the activate step
     
     --  activate bath that is near or past the suppliers recommended metal 
     turnovers or is that is significantly under operating temperature
     
     
     
     Michael Holan
     Radian International L.L.C.
     Electronics Division
     michael_holan @radian.com


______________________________ Reply Separator _________________________________
Subject: Re: electroless nickel finish
Author:  John Grosso <[log in to unmask]> at Internet
Date:    2/20/97 12:53 PM


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
     
*************************************************************************** 
* TechNet mail list is provided as a service by IPC using SmartList v3.05 * 
*************************************************************************** 
* To subscribe/unsubscribe send a message <to: [log in to unmask]>   * 
* with <subject: subscribe/unsubscribe> and no text in the body.          * 
*************************************************************************** 
* If you are having a problem with the IPC TechNet forum please contact   * 
* Dmitriy Sklyar at 847-509-9700 ext. 311 or email at [log in to unmask]      * 
***************************************************************************
     

***************************************************************************
* TechNet mail list is provided as a service by IPC using SmartList v3.05 *
***************************************************************************
* To subscribe/unsubscribe send a message <to: [log in to unmask]>   *
* with <subject: subscribe/unsubscribe> and no text in the body.          *
***************************************************************************
* If you are having a problem with the IPC TechNet forum please contact   *
* Dmitriy Sklyar at 847-509-9700 ext. 311 or email at [log in to unmask]      *
***************************************************************************