On a closely related topic, we've been working with Intel on issues related to strain/deflection of the PCB around BGAs. This has become a critical issue for RoHS parts and processes. Some overview information can be found at: http://www.smta.org/files/oregon_chapter_presentation0615-1.pdf Frank Joyce is very willing to work with other interested parties in the industry on this. Industry Guidelines: IPC/JEDEC 9704 contains the Printed Wiring Board Strain Gage Test outlines (how to perform tests). IPC/JEDEC 9702 contains the Monotonic Bend Characterization of Board Level Interconnects. Thanks, Cheryl Tulkoff Senior Reliability Engineer Phone:(512) 683-8586 Fax: (512) 683-8847 National Instruments 11500 N. Mopac Expressway Building A Austin, TX 78759-3504 "Brooks,Bill" <[log in to unmask] > To Sent by: TechNet [log in to unmask] <[log in to unmask]> cc Subject 02/10/2006 01:00 Re: [TN] Populated PCB deflection PM spec? Please respond to TechNet E-Mail Forum <[log in to unmask]> ; Please respond to "Brooks,Bill" <[log in to unmask] > Alan, I will attempt to address your question as best I can given the information you provided. A properly designed non-flexing enclosure with rigid mounting for the board should restrain the rigid board from flexing. If it isn't properly restrained, it isn't designed correctly to survive for long. How long must it survive the potential stress it will encounter? Which particular mode of 'flexing' are you most concerned about? A pressure from a human finger pressing a switch or button? Or, perhaps the flexure that happens under continuous sinusoidal vibration at some given frequency? Or perhaps instantaneous shock of some given number of g-force in inch/lbs? Or simply the expansion and contraction of the material over temperature... perhaps all four? The survival of the circuit depends on it NOT being stressed beyond its ability to recover intact. Work hardening of solder joints and the components mounted to the board through that solder joint can cause them to fail. Repeated flexing can cause breakdown of the epoxy/fiberglass board, glass fibers, or other materials, or even the copper conductors and their adhesion to the board material can suffer from work hardening and structural failure can be a possibility... if the vibration is intense enough and sustained over a long period of time. As far as my seeing a spec that calls out an acceptable maximum single flexure of a rigid board electrical assembly, I really have not seen anything that specifies a restriction on that particular design feature. Most requirements are saying that it must not fail given a certain maximum or minimum environmental exposure. If you were using Flex circuit materials it would really be able to survive a lot of flexing, but the components might not... it all depends on how you protect the solder and components from being exposed to undesirable stresses that cause failures. Your board may survive a tremendous flex of many inches... once, or twice, but if you repeat it over and over, eventually you will find the breaking point and the weakest link will fail. Each board will be different depending on the modulus and tensile strength or even ductility of the materials involved and what amount of stress is being applied to the assembly and where and how often and at what temperature and humidity. Sorry it isn't a simple yes or no question... I don't suppose that any of that helped with your question a bit. Best regards, Bill Brooks - KG6VVP PCB Design Engineer, C.I.D.+, C.I.I. Tel: (760)597-1500 Ext 3772 Fax: (760)597-1510 Datron World Communications, Inc. _______________________________________ San Diego Chapter of the IPC Designers Council Communications Officer, Web Manager http://dcchapters.ipc.org/SanDiego/ http://pcbwizards.com -----Original Message----- From: Alan Young [mailto:[log in to unmask]] Sent: Friday, February 10, 2006 9:49 AM To: [log in to unmask] Subject: Re: [TN] Populated PCB deflection spec? Hi, Here is a question that has just popped across my desk from an engineer. A board has been populated (All SMT - 0402's, BGA's, etc.) mounted into its housing on stand-offs. How much deflection is acceptable if the board has not been properly supported in the middle? Is there a specification for this? Thanks In Advance. Alan. --------------------------------------------------- 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 -----------------------------------------------------