I would suggest that the 1.56 microgram value was a default suggestion for all three classes of hardware and is easily achieved. There is substantial data suggeseting that as the PWA designs go to tighter spacings (circuit and part/board) and higher speeds, this requirement will probably get tighter. Below is a summary of some literature on this subject that I collected for our management. a) "For bare PWB levels of contamination in the 1 microgram NaCl (eq)/ cm2 ranges (6.45 microgram/in2 )...are reasonably consistent with leakage requirements of today's devices."- A Correlation between Surface Insulation Resistance and Solvent Extract Conductivity Cleanliness Test, A. Chan and T. Shankoff, Circuit World, Volume 14, #4, 1988, pp. 23-26 b) Summary of Contamination Limits; Process Stage: Bare PWBs before solder mask, contamination limit (actual production) 1 microgm/cm2 (6.45 microgram/in2); after assembly limit is 1.5 micrograms/cm2 - Bellcore Standard TR-NWT-000078 c) "Many assembly manufacturer's use a bulk resistivity limit of 1.0 to 3.3 microgram/square INCH of NaCl as their cleanliness requirement test for incoming boards" - Component Cleanliness, T. Munson and M. Ford, Circuits Assembly, March 1993 d) "(Permissible Ionic Contamination) For surface mounted assemblies this level is better set at 0.5 microgram/cm2..." - A Scientific Guide to Surface Mount Technology, C. Lea, Electrochemical Publications, 1988 e) (Suggested Arbitrary Limit Values for Ionic Contamination as Measured by a Commercial Instrument) Aerospace/military applications - 1 microgram/cm2 Ultra-critical SMC application - 0.5 microgram/cm2 - Cleaning and Contamination of Electronic Components and Assemblies, B. N. Ellis, Electrochemical Publications, 1986 f) "...a chloride contamination of greater than 4 microgram/in2 resulted in a loss of insulation resistance, development of corrosion and blistering in the conformal coating." - Evaluation of Salt Contamination on Insulation Resistance, C. Littlefield, EM/P 120, (~1975) g) "A study done by the Naval Weapons Center (China Lake, CA) showed that certain types of fluxes used in PWB processing would fail SIR testing even after meeting the requirements of MIL-P-28809" - No Clean Fluxes: New Technology Needs New Test, E. Small, Circuits Manufacturing, December 1989 ______________________________ Reply Separator _________________________________ Subject: PCBA Ionic Contamination Levels Author: [log in to unmask] at esdigate Date: 10/3/95 3:41 PM ANSI/J-STD-001 and other specifications require ionic contamination levels of less than 1.56 micrograms/cm2 (10.06 micrograms/in2). This is a reasonable level for overall ionic contamination on Class 3 PCBA's, and is a good maximum level for monitoring the cleaning process. But, what about maximum levels for Class 1 (Consumer) and Class 2 (Industrial) grade PCBA's ? Afterall, there are different levels for rosin residues. Does anyone have ACCEPTABLE (maximum) levels for ionic contamination on Class 1 and Class 2 PCBA's ? Thanks . . . Ed Valentine ([log in to unmask]) ProTronics, Inc. Knightdale, NC Phone: (919) 217-0007, FAX: (919) 217-0050 ******************************************