Hi I will try to help you. Solder Balls it has been the most common and the most complex reflow soldering problem. During reflow, small spherical solder powder particles of various diameters, are formed away from the main solder pool, do not coalesce and remain on the board after solidification. There are many possible causes such as: Smearing of paste on the PCB from an inadequate printing process (stencil underside wiping between prints can often alleviate this), excessive exposure of paste to an oxidizing environment, inadequate heating (too slow and uneven), too rapid a heating rate and too long a preheat profile, prompting paste dry-out. Other causes of solder ball formation include an interaction between the solder mask (as you said) and paste, insufficient flux activity, too many fines (undersized powder particles) and inappropriate volatiles in the flux for the specified reflow process. The presence of solder balls on the PCB is of concern because of their potential for creating circuit shorts and/or leakage currents. They also represent the possibility of insufficient solder in an adjacent joint that ought to have been part of a well-formed connection. I hope this will help you, Rub?n E. Irizarry-Guzm?n Operations Engineer [log in to unmask] on 03/16/98 08:06:30 AM Please respond to [log in to unmask]; Please respond to [log in to unmask] To: [log in to unmask] cc: (bcc: Ruben Irizarry) Subject: [TN] Causes & Corrective Actions for Solder Balls Good day all, I have a question relative to solder balls and hope that someone can shed some light on this issue. 1. What causes solder balls? 2. Could solder balls be the result of incompatiability between flux and soldermask? 3. How do you eliminate solder balls? 4. What is the IPC acceptability standards for solder balls? Any feedback would be greatly appreciated. Thanks to all that offer assistance. Best Regards ################################################################ TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c ################################################################ To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body: To subscribe: SUBSCRIBE TechNet <your full name> To unsubscribe: SIGNOFF TechNet ################################################################ Please visit IPC web site (http://jefry.ipc.org/forum.htm) for additional information. For the technical support contact Dmitriy Sklyar at [log in to unmask] or 847-509-9700 ext.311 ################################################################ ################################################################ TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c ################################################################ To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body: To subscribe: SUBSCRIBE TechNet <your full name> To unsubscribe: SIGNOFF TechNet ################################################################ Please visit IPC web site (http://jefry.ipc.org/forum.htm) for additional information. For the technical support contact Dmitriy Sklyar at [log in to unmask] or 847-509-9700 ext.311 ################################################################