Hi, Steve I wanted to clear up a common assumption, very common but not always true. Preheating SMT chip caps and resistors to 130-150 deg. C. and immersing them in 500 deg. F (260 C) molten solder for (typically) 2-3 seconds in the wave solder process is not always worse than subjecting them to convection reflow temperatures (especially those where the MRT is above 225 C for more than 30 seconds) for a full 7-8 minutes or longer. I have had more instances where the convection reflow process induced or contributed to reliability issues more often than I have with wave solder. There have been several times where I saw component fallout on parts that were convection-reflow soldered, whereas the same part never failed when wave-soldered on other assemblies. With a small contribution to the Doug Pauls Mountain Dew Fund, it depends on the components and the circuit board type. But I do agree with your statement that a good selective wave fixture that protects the part is usually the best option. -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Gregory Sent: Monday, June 16, 2008 10:05 AM To: [log in to unmask] Subject: Re: [TN] Glue Mask Requirements Hi Natasha! Most of the time, I just leave it up to my stencil vendor to create my epoxy stencils for me when I have to use them. They do that from the solder paste layer. Personally, I try to avoid using epoxy whenever I can, I just do a double-sided reflow if there is SMT components on both sides of the board. If I need to wave the board and the volume justifies it, I'll get a selective wave solder fixture made which will mask off the SMT on the bottom of the board. If it's a low volume board, and depending on the amount of PTH components there are, I'll just have the PTH hand-soldered. A few reasons I don't like using glue are: - It's messy - There always seems to be handling issues with the boards after the parts are epoxied on. - It can't be too good on SMT parts being immersed in a 500-degree wave Steve -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Natasha Baker Sent: Monday, June 16, 2008 8:25 AM To: [log in to unmask] Subject: [TN] Glue Mask Requirements Hi All, I have a question regarding the glue mask when designing PCBs. I am ordering the IPC SM-817 which provides requirements for surface mounting adhesives, but am unsure if it will provide requirements specifically on dimensions for the glue mask. Are there concrete rules for glue mask dimensions? Or, should the glue mask just follow the component outline? Also, is it always necessary to use a glue mask, or only when components are placed on both sides of the board? Best Regards, Natasha --------------------------------------------------- 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 -----------------------------------------------------