Do we have an IPC test method to cover the measurement of localized flatness? If not, do we need one? Mike Hill -----Original Message----- From: IPC-600-6012 [mailto:[log in to unmask]]On Behalf Of Montgomery, Scott D Sent: Wednesday, May 10, 2006 6:02 PM To: [log in to unmask] Subject: Re: [IPC-600-6012] IPC-6012B Bow and Twist Requirements I also concur that not all designs need to be tighten. If there is a concern for bow and twist for a specific family of components, we will define a localized flatness for those component areas on the fab drawing. This has worked very well. My recollection is that less than 5% of our boards were scraped by the fabricator due to out-of-spec flatness. Thanks Scott -----Original Message----- From: Mark Harvey [mailto:[log in to unmask]] Sent: Wednesday, May 10, 2006 2:43 PM To: [log in to unmask] Subject: Re: [IPC-600-6012] IPC-6012B Bow and Twist Requirements Concur. If a design requires a tighter tolerance than they should identify that on the print or by spec. Forcing all product to that will drive up cost for all. True story some designs do need a tighter tolerance. -----Original Message----- From: Franklin D Asbell [mailto:[log in to unmask]] Sent: Wednesday, May 10, 2006 1:15 PM To: [log in to unmask] Subject: Re: [IPC-600-6012] IPC-6012B Bow and Twist Requirements I don't believe tightening these requirements would benefit all companies as a whole. The problems I've seen experienced are isolated to specific designs, on specific equipment. I would propose something more clarified in respect to customers (i.e. assemblers) and suppliers reviewing designs more closely together. Customer A may have equipment to handle a certain amount of warp (as noted below) while Customer B may not, Customer B could then tighten this specific tolerance to a certain supplier who might make adjustments for a certain amount of additional processing or even yields. A general tightening of bow/twist may cause acceptable product to be scrapped that might otherwise be used if pre-fabrication including fabrication requirements discussions were performed. Franklin D Asbell -----Original Message----- From: IPC-600-6012 [mailto:[log in to unmask]] On Behalf Of John Perry Sent: Wednesday, May 10, 2006 2:49 PM To: [log in to unmask] Subject: [IPC-600-6012] IPC-6012B Bow and Twist Requirements Colleagues, IPC continues to receive queries from industry as to whether or not there will be a tightening of the bow and twist requirements for printed boards that are given in both IPC-2221A and IPC-6012B. I would like the members of this forum to provide their feedback on these requests. There are currently two arenas where we are getting requests for alteration to the requirements: BGA devices and screen printing technology. Regarding BGA technology, Don Dupriest of Lockheed Martin Missiles and Fire Control provided a .ppt file at the IPCWorks 2005 meeting for these groups where the recommendation for bow and twist acceptance for isolated BGA areas is 0.50%. This presentation file is available at http://www.ipc.org/committeedetail.asp?Committee=D-33A Within "Drafts", under the titled "PCB Bow and Twist - BGA Devices" Regarding screen printing technology, we recently received the following request: We had a board that was slightly warped, make contact with and damage the camera in one of our screen printers. Of course, when I measured the bow and twist, it was well within acceptable limits for bow and twist. My question is this: Are the bow and twist specifications tight enough? For over 15 years, I have been "jumped on" by the line operators and maintenance guys to fixed warped boards only to find that the boards are usually not any where near the limits. Since I have worked for multiple companies, I see that this is an industry wide dilemma. Board manufacturers typically can hold bow and twist requirements, but different SMA machines (especially screen printers) aren't able to run a board that has bow or twist near but within the specification limits. Should I be asking why machines built for the surface mount industry can't run boards that meet industry specifications, or if the specifications that once fit, are in need of revision? Larry D. Roberts Quality Engineer Andrew Corporation Thanks for taking the time to review and respond to these industry requests. Regards, John Perry Technical Project Manager IPC 3000 Lakeside Drive # 309S Bannockburn, IL 60015 [log in to unmask] 1-847-597-2818 (P) 1-847-615-7105 (F) 1-847-615-7100 (Main) ________________________________________________________________________ ____ _ Scanned by Sanmina-SCI eShield ________________________________________________________________________ ____ _ ________________________________________________________________________ _____ Scanned by Sanmina-SCI eShield ________________________________________________________________________ _____