Within the new IPC spec for PWB handling there will be instructions for how to determine the optimum bake time/temperature for any given PWB. This procedure will allow you to scientifically determine the optimum bake time to get to a moisture level less than 20%. It will also tell you how to determine just how long any given assembly or circuit board can remain out, unprotected from humidity, before it should be re-baked, and just how to determine the bake time based on the time exposed. For most substrates, a moisture level less than 20% of its saturated moisture weight is usually sufficient to prevent damage during reflow, wave solder, or hot gas rework. Of course, this is a guideline. There could be some substrate materials out there where a moisture content above 20% of saturated weight can lead to damage during thermal excursions, but I cannot find any information or data suggesting that. So there will be a caveat within the procedure that a sample should be tested to qualify the process for "unusual substrate materials". Following this procedure will allow you to determine the shortest/lowest acceptable time/temperature such that the amount of oxidation is minimized, and the amount of baking that could possibly be harmful to the PWB or the CCA is minimized. -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Joe Macko Sent: Thursday, August 28, 2008 11:46 AM To: [log in to unmask] Subject: Re: [TN] Moisture in PCB Assemblies Denny, We have always treated FR4 PCBs as moistures sensitive and baked them out before reflow to be safe. Everyone has there own idea about bake out time and temperature and most CMs do consider the PCB moisture sensitive. We bake for 5-6 hrs at 110 C. Boards are generally used within 2-weeks of bake out. Best Regards, -joe "This e-mail and any attachments are solely for the use of the addressee and may contain L-3 proprietary information that may also be defined as U.S. Government export controlled technical data. If you are an unintended recipient of this e-mail, use, disclosure or distribution of its content is prohibited. Please notify the sender by return e-mail and immediately delete this message." From: TechNet [mailto:[log in to unmask]] On Behalf Of Dennis Fritz Sent: Wednesday, August 27, 2008 7:10 AM To: [log in to unmask] Subject: Re: [TN] Moisture in PCB Assemblies Bill, There has been some speculation that with the higher assembly temperatures of lead-free, that PCBs should have a Moisture Sensitivity Level - just like the components being mounted on them.? However, I don't think JEDEC will step up to the plate to adopt anything to do with PCBs.? So, it would be the job of the IPC to do that.? With the upcoming IPC meeting in late September, Schaumburg, Illionois, now would be a good time to debate the need for circuit board MSL levels. As pointed out, the group working on Storage and Handling will go a long way, but moisture absorbsion propensity is also a property of the resin/glass composition of the board.? How about it TechNetters? Denny Fritz MacDermid, Inc. -----Original Message----- From: [log in to unmask] To: [log in to unmask] Sent: Tue, 26 Aug 2008 7:19 pm Subject: [TN] Moisture in PCB Assemblies Fellow TechNetters:? I was asked a question by a valued customer if there is any other references made to moisture in raw PCBs and populated assemblies other than the J-STD-033 and also the IPC rework standards.? I've looked in IPC Standards I have on file however I could not find any references/guidlelines at all.? Can anyone out there shed some light on this??? I thank you folks in advance for your efforts on my behalf. Bill Black Medco Q.A. Manager Tel:? 631-667-9699 E-Mail:? [log in to unmask] --------------------------------------------------- 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 ----------------------------------------------------- -----Original Message----- --------------------------------------------------- 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 -----------------------------------------------------