Hi John, Be careful your 'modified fixture' allows unrestrained expansion in the x and y planes, otherwise the constraint of movement in this plane will want to pop the board up or down in the z direction. If that movement is constrained too, you could build up damaging internal stress levels as the board fights the constraints. Since your solder joints have probably cooled in a deformed shape to match the warped board, I think your plan to go up to the liquidus point of your solder is a good one. Alternately, you could try and heat the board to a lower temperature (110 degrees say, for FR-4 with a Tg of 125 - just enough so the FR-4 is soft enough to remould in a flatter shape) very slowly (so that board deformation change is less than the creep rate of solder) and allow the creep properties of the solder to allow SJ movement to the new board shape. Others on this list (Werner are you there?) probably have some good input on those 2 different strategies. In either case, I think you'd want to control the cool down rate very carefully (i.e. do it slowly), to try and keep the temperature through the thickness (z direction) of the board as uniform as possible. For bare boards, the most severe warpage is typically noted around Tg (say 120-125 for difunctional FR-4) because there are dramatic changes in the mechanical (young's modulus and shear modulus) and thermal (CTE) material properties around this temperature. Thus, even relatively small temperature differentials can create temporarily highly unbalanced lamina stacks. So if you go up to 220, slow your cooling rate to its lowest value between 145 and 105 degrees C. (for 125 Tg material). Good luck! Andy ---------- From: [log in to unmask] [SMTP:[log in to unmask]] Sent: Thursday, October 09, 1997 4:28 AM To: [log in to unmask] Subject: [TECHNET] Fixing Warped Assemblies Address, I have a recent lot (100 pieces) of assemblies with enough warp in the longest edge to keep the assembly from plugging into the backplane. As a flag, the warp should have been caught by operators following Wave, but was not. I have a solution to ensure future assemblies are not affected. I am also in the process of modifying the Wave fixture for low mass assemblies and the Wave Process Flow Procedures. There are three options I have come up with to (temporarily) fix the warp problem, such that the field engineers can insert the assemblies. OPTIONS: 1. Bake assemblies in oven at X temperature for X time with applied weight; or 2. With the modified wave fixture, which ensures rigid stability in all regions, re-solder assemblies via wave soldering; or 3. Run assemblies through the Convection Reflow Oven at X temp for X time with the modified fixture holding the assembly in place I have opted to go with Option 3 and would like to hear others experience(s) or any other avenues of thought. I am thinking the assemblies shall be run at a maximum of 220?C for 55secs max. (ramp up temp/time is not included) at 1.12cm/sec using a Heller 1500 Reflow Oven. My insanity is to bring the fab temperature as close to the fabs Tg to minimize if not eliminate any Warp Memory. Granted, this is another thermal excursion, but lets approach as if there are no alternatives and components can withstand. Thank you John Gulley Inet Inc. Plano, TX 75075 972-578-3928 ############################################################## TechNet Mail List 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 web site (http://www.ipc.org/html/forum.htm) for additional information. For the technical support contact Dmitriy Sklyar at [log in to unmask] or 847-509-9700 ext.311 ############################################################## ############################################################## TechNet Mail List 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 web site (http://www.ipc.org/html/forum.htm) for additional information. For the technical support contact Dmitriy Sklyar at [log in to unmask] or 847-509-9700 ext.311 ##############################################################