Most conformal coating chemistries are compatible with SMT, with the possible exception of rigid resins such as acrylic (AR) and epoxy (ER). Resilient materials such as silicone (SR) and urethane (UR) work very well. For ultimate protection, you may consider Paraxylene (XY) - but only as a last resort. Paraxylene requires a very specialized application process ($$$$$). The key is to provide the printed wiring assembly with effective coverage and protection for the expected operating environment, without adversely affecting component strain relief or thermal dissipation. For conformal coating, more is not necessarily better, and thin coatings are better than thick. All conformal coatings present some mechanical load to the component's leads and solder joints, and have a thermal "blanketing effect" by reducing the assembly's ability to dissipate heat. Because of the increased thermal density of SMT, anything that impedes the ability to shed heat must be understood and taken into consideration of the overall design. Obviously, you would not want to use a coating design that would cause a device (or board) to overheat and fail. Also, you and your customer must decide how much pain you are willing to endure if rework is desired. Silicone and urethane is easily removed and replaced for rework, paraxylene is extremely difficult to cut through and boards coated with paraxylene are generally considered "unrepairable". Bob Cooke -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Douglas O. Pauls Sent: Monday, July 12, 2004 7:43 AM To: [log in to unmask] Subject: Re: [TN] conformal coating on SMD Yes they can. There are dozens of varieties and chemistries of coatings. I suggest that you get a copy of the IPC Conformal Coating Handbook for further education. Doug Pauls Murulidhara <rpcblab_bgp@ITIL To: [log in to unmask] TD.CO.IN> cc: Sent by: TechNet Subject: [TN] conformal coating on SMD <[log in to unmask]> 07/12/2004 03:59 AM Please respond to "TechNet E-Mail Forum."; Please respond to Murulidhara Dear Technetters, I want know whether PCB assemblies with surface mount components can be conformal coated. If so, what type of conformal coating compound for SMD components? Thabks in advance --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 1.8e 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 847-509-9700 ext.5315 ----------------------------------------------------- --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 1.8e 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 847-509-9700 ext.5315 ----------------------------------------------------- --------------------------------------------------- Technet Mail List provided as a service by IPC using LISTSERV 1.8e 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 847-509-9700 ext.5315 -----------------------------------------------------