You probably need to perform a gage R&R to know whether the scale is going to be usable for this experiment. If 3 people could measure the same 5 serialized samples 5 times, in randomized order of samples each time measured and randomized sequence of people to measure, you could determine the minimum difference in weight the scale can discern. The rule of thumb is you need resolution 4x the difference you expect to measure, and is preferred to be 10x the difference expected. Dick Krug, CSSBB, CSMTPE SMT Process Engineer Sparton Corporation 30167 Power Line Road Brooksville, FL 34602-8299 p (352) 540-4012 (Internal Ext. 2012) [log in to unmask] -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Robert Kondner Sent: Monday, January 30, 2012 1:02 PM To: [log in to unmask] Subject: [TN] Measured Water on Board after Rinse Hi, I finally received my little scale with .01g resolution. Not a lot but good enough for government work! J So I took a small board I make, 2 x 2 inches, weighted, rinsed, shook off and air gunned. (26cm sq) See: www.kondner.com/files/smallbrd.jpg Initial Weight: 17.81 gram After Rinse and shake: 18.00 After blow off: 17.83 After blow off I had .02g of water. Given my poor scale resolution let say .03g or .03ml. After the board dried some I noticed it was down to 17.80. I must have removed some dust. Assuming really poor rinse water at 100mg of NaCl equiv per L we can expect 3 * 10**-6 g or 3 ug on the 26 cm sq PCB. Actually the surface area with the second side and parts is probably several time that but let's use just the two sides of the PCB or 52 cm sq. Wow even without the water blow off the tap water is a non-issue. If I simply rinse in distilled I am fine. Good, I can trash the blow off process if rinse in distilled. 3ug / 52 = .058 ug / cm sq Holy Cow, did I get all the conversions and math right? Actually the final water related remaining contamination is probably 10% of that as most tap water is cleaner and not all dissolved solids ate as ionic as NaCl. The normal NaCl found in epoxy laminates or uncured solder mask and silk screen ink Ionics are probably more of a problem. Summary: Rinse water quality is only a TINY fraction of what goes into total board cleanliness. It is not the quality of the rinse water. The quality of the wash, getting the wash material FLOWING under parts is the killer. And getting the contaminated wash water removed is VERY important. As for the nature of the rinse water it is a complete don't care. Bob K. OK: Tear into me. I saw the movie "The Grey" with my son over the weekend. I am ready to be attacked by a pack of wolves. J ______________________________________________________________________ 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] ______________________________________________________________________ --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 16.0 To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives For additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 ----------------------------------------------------- ______________________________________________________________________ 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] ______________________________________________________________________ --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 16.0 To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives For additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 -----------------------------------------------------