Dear J.Janoch,

These spots are came probably due to the improper cleaning of the stencil
during the past printing process. 

It can be avoided by the  proper cleaning of the stencil by a lint free
clothe from bottom sideand make sure that no particle of solder paste should
be there.

or 

cover the gold contact area by Kapton tape before the past printing and
remove it latter on.

Br
Pankaj 

> -----Original Message-----
> From: Janoch Jirí, Ing. [SMTP:[log in to unmask]]
> Sent: Thursday, February 17, 2005 5:53 PM
> Subject:      Sn sputtering
> 
> Hello Techneters,
> could anyone solve this problem, please ? We solder PCB assembly in the
> reflow oven. PCBs have ENIG surface contact pads including solder pads.
> After reflow,  soldering is perfect, but random fade Sn spots are on the
> gold contacts. Is this phenomenon usual for reflow soldering and how to
> avoid this
> Sn sputtering ?
> Many Thanks
> J.Janoch, TSE
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