Daan, Boards which are badly warped then post-baked for stress relief will warp again once heat is applied. If these see more than one heat cycle, the second pick and place operation could be a very large problem. We have also been concerned (although we have no data) that boards with high pin count small ball BGAs may suffer fractured joints once the board warps again in assembly and then cools post assembly. There are 2 possibilities about the material and the "inspections" - one is that the material itself did not meet the specifications. I have found that a board shop needs to have vigilance regarding the quality of the incoming laminate. Yes, it should all be ship-to-stock, but I have seen too many times when the laminate or prepreg was out-of-specification, it was shipped to the fabricator, and the fabricator used it. All of a sudden, on a part that was running fine, there is warpage. That should signal a review of the material; some testing; some tracability to see how many boards and which boards used that material etc. The fabricator should have a audit or quarterly (monthly? semi-annual?) test and qualification retention procedure for the laminate. Also, arrangements where the fabricator has turned over the laminate stores to the laminate supplier (they manage min/max levels based on counts or some other measure; and they are responsible for managing shelf-life and establishing a FIFO system) absolutely need to audit that department *as though it were not within it's 4 walls*. I have audited many shops and have found out-of-date prepreg on more than one occassion (sorry laminate makers - but you need tighter controls). The other possibility about "inspections" is that the layup person didn't "inspect" the material that was kitted for the job; an operator is responsible to pull all the materials (cores and prepregs) require to build up the panel, and those materials are grouped together and sent into the layup area. It is highly possible to kit the wrong prepregs when it is a manual operation. In that case the layup person may or may not have a procedure to verify the materials prior to making the multilayer. So, that could be the inspection step referred to. In that case the corrective action belongs entirely to the fabricator; they should have the controls to keep that from occuring. Prepregs that are "cross-plied" to each other will warp and that warp will only be temporarily disguised by a wieghted bake and will return again. You need to go deeper and have them say more about the root cause besides "inspections"? At what stage in the process? What are the inspections designed to find ? Valerie "d. terstegge" <[log in to unmask]>@listserv.ipc.org> on 05/22/2003 04:13:45 AM Please respond to "TechNet E-Mail Forum." <[log in to unmask]>; Please respond to "d. terstegge" <[log in to unmask]> Sent by: TechNet <[log in to unmask]> To: [log in to unmask] cc: Subject: [TN] Bad laminate and warped board Hi Technet, I recently received some boards that were warped outside the IPC specifications and I complained about it to the manufacturer. Their answer is that the problem was caused by variations in laminate and prepreg, where the operater didn't do the prescribed material-inspections. They will rework the boards by applying pressure at a temperature higher then Tg, to release the stresses in the material. Some questions: Whats' the proper way for a bare board manufacturer to control the quality of laminates and prepregs with regards to flatness ? Is it common practice to rely on an incoming inspection ? If a board is flattened, will it remain flat after soldering ? I know that with an unblanced design the problem will always re-occur, but I'm not sure what will happen when it's the laminate-quality that caused the problem. Daan Terstegge Thales Communications Unclassified mail Personal Website: http://www.smtinfo.net --------------------------------------------------- Technet Mail List provided as a free 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/html/forum.htm for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ----------------------------------------------------- --------------------------------------------------- Technet Mail List provided as a free 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/html/forum.htm for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 -----------------------------------------------------