Paresh Patel wrote: "We have one SM chip on our boards which is put on by a contractor. Lately, we are seeing excessive flux residues on and around the pads. The residues have look of frosted crystals. The flux used is a no-clean flux. Is it acceptable for these residues to be there? Will it create any problem now or later? What is acceptability standard?" You should determine the nature of the residue before making any conclusions but this information may be of some help. Alliant Techsystems participated in a CRADA, the final report is called "Evaluation of Low-Residue Soldering for Military and Commercial Applications:A Report from the Low-Residue Soldering Task Force." In the study, comparisons were made between 'low residue' assemblies that were cleaned prior to conformal coat and those that were processed without a cleaning step. One of the sub-groups processed at Alliant Techsystems was soldered using low residue flux and then cleaned using a solution of 75%IPA:25%water in an Ionograph. I did not work on the project, but, if I remember correctly, this sub-group was 'ugly' ( the residue from the no clean flux was only partially removed and had turned white) but performed well in the testing. At one time, copies of this report were being distributed by a member of the task force from Sandia National Labs but I think he has move on to a different organization. The report has been summarized in several trade magazines. If you need help locating a copy, you might ask the technical librarian at the EMPF ( 317-226-5623). Good luck. Mary Davis Sr. Materials & Process Engineer Alliant Techsystems 206-356-3311 e-mail: [log in to unmask] *************************************************************************** * TechNet mail list is provided as a service by IPC using SmartList v3.05 * *************************************************************************** * To unsubscribe from this list at any time, send a message to: * * [log in to unmask] with <subject: unsubscribe> and no text. * ***************************************************************************