I agree with your observations. We do prebake some boards, including all field returns requiring rework with convection or radiation transfer tools. But, not as a standard practice. J-STD-001 broaches the subject, saying that it can be done. The HDBK-001 expands on the information. Remember the IPC standards are consensus standards. The committees working on them understand that standard requirements end-up on contracts. So, work of the committees respects "The Principles of Standardization". These are listed on the inside front cover of the J-STD-001. The principles make it very difficult to make suggestions or recommendations within the text of a standard. I don't think there is a consensus for a standard requirement. They may be a consensus on good advice, for now. But, in a book it would become obsolete as materials improved, or changed (things will get worse with Pb-free solder for awhile). This is a good place to get current advice. My advice is to bake boards when you have reason to be concerned. 1. Bad past experience 2. High layer count and very expensive-rare components 3. Field return that requires hot air rework -----Original Message----- From: TechNet [mailto:[log in to unmask]]On Behalf Of Stadem, Richard Sent: Monday, October 10, 2005 10:34 AM To: [log in to unmask] Subject: [TN] (tn)(pwb) When do you need to bake a circuit board prior to assembly? Are there standards? Fellow technetters, some questions. I know that it is sometimes necessary to pre-bake pwb's when there is a chance that moisture could damage the board when it goes into reflow, or when it is subject to hot-gas rework. I understand most OEM's and CEM's do not bake as a matter of standard procedure simply because they usually do not need to, and baking will diminish solderability. Nearly all of the delamination issues I have ever seen were invariably caused by some type of prepreg lamination deficiency. Most of the time nearly any standard .062" multilayer FR-4 pwb can be reflowed without pre-bake without danger of delamination, at standard 63/37-based reflow temperatures. Typically the boards are still dry, and even if they are not, the prepreg holds up during reflow and rework. Are there standards for pwb handling that spell out what type(s) of prepreg materials should be used for different types of pwb's , what the proper storage methods are, when pre-baking should be performed, at what temperature and time, etc? Is there a standard that tells us that certain board types or configurations should be baked (or which ones do not need to be)? Is there anything out there that provides proper storage methods for pwb's? If no standard exists, should not there be one? --------------------------------------------------- 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 847-615-7100 ext.2815 ----------------------------------------------------- --------------------------------------------------- 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 847-615-7100 ext.2815 -----------------------------------------------------