In a message dated 1/20/99 5:12:47 PM Pacific Standard Time, [log in to unmask] writes: << We have been seeing boards come off our reflow oven with bow and twist that exceeds IPC specs. Our vendor insists that we are the only customer that complains about this. We had our reflow oven calibrated and it looked fine. The only thing about the profile that may be suspect is the cooling rate may be a little too fast. According to the vendor, they put all of their boards through a de-warping process. The vendor has tweaked their de-warping process to cool slower in an effort to make the problem go away. My question is: This is our first bout with warping, what should we be looking at for a cause? Is it normal for a pc board vendor to have to de-warp boards? Regards, Ken Nevius Veeder-Root Altoona, Pennsylvania >> Good Morning Ken! When you say the boards are exceeding IPC specs, is it that statement in the -610B that says: " Bow and twist after soldering shall not exceed 1.5% for through-hole and .75% for surface mount."? Is it just exceeding those specs, or is it truely creating a problem in the rest of the assembly process, or in the form, fit, and function at the end use of the product? The reason I ask is that there has been times in the past where the attention was focused purely on numbers in a spec, rather than looking at things from a practical point of view. We all would like to have boards that are flat as a pool table, but because of different things, many times that doesn't happen. I guess it could be caused by something your fab vendor is doing, but in my experience, most of the time it has something to do within the layout of the whole assembly. Either the copper isn't balanced throughout the fab, or with the way the component mass is distributed throughout the board. The above comments go without saying that the warping isn't being induced by doing something wrong in reflow such as running a heavy, dense, board on the edge rails without some sort of center support. But getting back to the warp itself, is it really causing a problem somewhere? Just as the statement says at the end of the paragraph about bow and twist in the -610B: "Before dispositioning completed assemblies with bow and twist as scrap, it is recommended to have in mind how the PWA's in question are mounted on their final destination run evaluations. Keep in mind form, fit, and function without jeopardizing reliability. Hope this helped a bit... -Steve Gregory- ################################################################ TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c ################################################################ To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body: To subscribe: SUBSCRIBE TechNet <your full name> To unsubscribe: SIGNOFF TechNet ################################################################ Please visit IPC's web site (http://www.ipc.org) "On-Line Services" section for additional information. For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312 ################################################################