Michael, A quick guess is you have smears of solder paste or a paste slump that leaves a paste web. It might be related to a temp profile that sputters the paste of drives off the flux before reflow. I assume you just started using a new paste from your description, you might keep searching. I don't know about the acceptability of small solder balls but they sure don't look good. I had an old paper on Solder Beading, see: www.kondner.com/files/Solder_Beading.pdf Not exactly what you are seeing, the beads are typically larger than what paste smears leave. But, it might help Bob K. -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Forrester, Michael (H USA) Sent: Wednesday, November 30, 2011 10:39 PM To: [log in to unmask] Subject: [TN] Real World Acceptability of Solder Balls. I have a PCA 6"X4" with a 144 pin LQFP on it. The lead spacing is 0.5 mm which leaves about 0.2 mm space in-between the pins. The board goes through SMT reflow and a selective wave. We are seeing various degrees of solder balls/spheres. The balls we see are basically two sizes 40-45um and 70-80um. The solder paste is a size mesh 3, which would explain the smaller balls. At this time I am not sure where the larger ones are coming from? We see around the LQFP any where from 2-5 balls and literally hundreds of balls. The solder paste is a no-clean and then the board is cleaned. The reason for using no-clean is because of the process wait time from reflow to cleaning. The vendor does not want to leave an aqueous flux on the board for an extended period of time. My basic question is: Is there an IPC specification(or general rule of thumb) on the acceptability of solder balls? I understand that the presence of solder balls is a process indicator and that IPC-610 states: Solder balls are not entrapped, encapsulated or attached or can become dislodged in the normal service environment. Does this really mean that if I find a single ball that is not entrapped/attached, this is a reason for rejection? Is this practicable or is there a spec./industry standard that says something like if you have X balls smaller than X in an area X, this is acceptable? In the real world, are companies holding the zero tolerance on solder balls? Thank you in advance. Best Regards, Michael Forrester Sr. Product Engineer CSMTPE Siemens Healthcare Diagnostics 101 Silvermine Rd. Brookfield, CT 06804 PH: (203) 740-6452 ---------------------------------------------------------------------------- --- This message and any included attachments are from Siemens Healthcare Diagnostics and are intended only for the addressee(s). The information contained herein may include trade secrets or privileged or otherwise confidential information. Unauthorized review, forwarding, printing, copying, distributing, or using such information is strictly prohibited and may be unlawful. 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