Too true. It's due to the fact that UR materials are generally solvent-resistant, whereas AR materials generally have little or no solvent resistance, hence the ease of rework. All that you are doing adding a UR over an AR is re-solvating the acrylic material with the solvents in the UR. So you then have a mixture of acrylic and UR polymers in solvent and as the solvent evaporates you get a combination of chemistries left behind. The two polymer types are rarely compatible, and you would usually end up with either a very hazy coating or a gooey mess as Ramon describes (technical term, we use it often ;-) Best Regards, Phil. -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Dehoyos, Ramon Sent: 05 March 2007 14:15 To: [log in to unmask] Subject: Re: [TN] Use of Type AR Conformal Coating for Military PCBs UR over AR does not work. The coating combination becomes gooey. AR over UR works well. Ed Mines can explain the chemical aspects of this result. Ramon -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Hernefjord Ingemar Sent: Monday, March 05, 2007 8:51 AM To: [log in to unmask] Subject: Re: [TN] Use of Type AR Conformal Coating for Military PCBs Echo... Except for Toluene....banned in Europe...we use a Thinner. Inge -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Douglas O. Pauls Sent: den 5 mars 2007 14:36 To: [log in to unmask] Subject: Re: [TN] Use of Type AR Conformal Coating for Military PCBs Good morning Les, Rockwell Collins is one such company. Many of our military products require a type AR coating for reworkability. We have used Humiseal 1B31 successfully on military product for many years. We have applied by HVLP spray, automated/programmable spray, dip coating, and brush coating. You can get the minimum 1 mil by brush coating with the as-supplied viscosity. You have to thin the material to spray, but you can usually get the minimum 1 mil in a single pass. Any adverse concerns (e.g., solder joints, solder mask, etc.)? Not really. The biggest concerns are flooding of connectors as the material spreads and wicks. Any humidity test results? Yes. We regularly pass MIL-STD-810 and DO-160E humidity testing. Method of coating removal? The material dissolves in toluene so most rework methods involve first dissolving the material in toluene. Rework using either AR or UR coatings. We recoat with 1B31 after rework. I have not investigated rework with a UR over 1B31. Doug Pauls - Bogert <[log in to unmask]> Sent by: TechNet To <[log in to unmask]> [log in to unmask] cc 03/02/2007 04:55 Subject AM [TN] Use of Type AR Conformal Coating for Military PCBs Please respond to TechNet E-Mail Forum <[log in to unmask]> ; Please respond to - Bogert <[log in to unmask]> March 2, 2007 I am seeking info on any military folks who coat their assemblies with Type AR coating. How do you apply it/ how many spray coats on each side of the assembly are needed to achieve the min J-STD-001 thickness? Any adverse concerns (e.g., solder joints, solder mask, etc.)? Any humidity test results? method of coating removal? Rework using either AR or UR coatings. --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 15.0 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 Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 ----------------------------------------------------- --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 15.0 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 Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 ----------------------------------------------------- --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 15.0 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 Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 ----------------------------------------------------- --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 15.0 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 Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 ----------------------------------------------------- --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 15.0 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 Please visit IPC web site http://www.ipc.org/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815 -----------------------------------------------------