Flux specs such as IPC J004 are qualitative rather than quantitative. In other words what the residue does/doesn't do is measured, not how much of it is there. I offer the following for information. Some paste suppliers give percent residue remaining numbers for their products but this is by no means consistent. Not all do and those that do don't do it on every product! As a guide a resin based no clean will leave about half its starting flux content as residue, usually slightly more. The number will go up and down slightly according to product. Small changes can also be made with profile. Low residue types are, but require inert atmosphere to make up the loss of protection from the resin. They are not much used in SMT. When evaluating residues by TDS number you need to make sure that your "units" are the same. Some suppliers reference a percent of the flux and others of the paste. The 50% number I quoted is of the flux. Remember that in round numbers the flux is only 10% of the paste so as a proportion of the paste that would be 5%, which sounds pretty good. It will look a lot more though. This is by weight; by volume the flux/solder ratio is closer to 50:50. So if the starting flux is half the printed volume and half of that remains after reflow that's 25% of the print volume remaining. The residues can also be in slightly different places. They can spread out, sit on the joint and so on. Sod's Law (Murphy's in US) predicts that if its important residues will be where you don't want them. In your case under devices :) Whether this has any significance in manufacturing or service life you will have to determine. Regards Mike Fenner Bonding Services & Products M: +44 [0] 7810 526 317 T: +44 [0] 1865 522 663 -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Thayer, Wayne - IS Sent: Monday, November 05, 2012 11:50 PM To: [log in to unmask] Subject: [TN] Limits on flux residue Is there a spec somewhere which limits the amount of residue allowed for no clean processing? I just saw a board where a BGA was about 70% "underfilled" by flux residue. No, this was not a flux/underfill product! A quick look at JSTD-001 Section 8 didn't seem to have specific guidance on this condition. Wayne Thayer ________________________________ Email addresses of ITT Exelis employees have changed from itt.com to exelisinc.com. Please update your favorites and contact information to reflect these changes. This e-mail and any files transmitted with it may be proprietary and are intended solely for the use of the individual or entity to whom they are addressed. If you have received this e-mail in error please notify the sender. Please note that any views or opinions presented in this e-mail are solely those of the author and do not necessarily represent those of Exelis Inc. The recipient should check this e-mail and any attachments for the presence of viruses. Exelis Inc. accepts no liability for any damage caused by any virus transmitted by this e-mail. ______________________________________________________________________ This email has been scanned by the Symantec Email Security.cloud service. For more information please contact helpdesk at x2960 or [log in to unmask] ______________________________________________________________________ ______________________________________________________________________ This email has been scanned by the Symantec Email Security.cloud service. For more information please contact helpdesk at x2960 or [log in to unmask] ______________________________________________________________________