Howdy Vic., Here are some insights I have on this subject. Q: I just wonder if it is possible to forget all the preheat, ramp up periods and go straight into the spike zone where solder paste will melt at that temperature? A: I don't think it's wise to do that. Typically, the thermal profile is defined by the flux chemistry. Each stage of the profile has a specific purpose. For example: Preheat - to fully preheat the SMT assembly to temperature 100 to 150C Soak - to ensure flux activation and achieve uniform heating Reflow - accomplish solder reflow (for 63/37=> 183 C) Cooling - to allow fine grain form within joint If you go directly into the "spike zone", you will experience one or more of the following problems. (Depend on your time) - Cold Solder - Solder Balls - Solder Splash - Board Warp - Component Crack The key to have a perfect profile is to have uniform heat transfer throughout the board. If you are really interested in removing preheat and ramp up periods, you should try Vapour Phase soldering where time is the main parameter of control. Hope this helps !! Michael Yuen ---------- From: TechNet-request To: TechNet Subject: Changing of reflow profile. Date: Monday, July 01, 1996 10:38PM Hi, I am a student doing research at the temperature issue during the IR reflow process. As I know that there is a well-defined temperature profile for the PCB when passing through the oven. I just wonder if it is possible to forget all the preheat, ramp up periods and go straight into the spike zone where solder paste will melt at that temperature? What are the potential problems I have to face in this context, excluding the thermal mass issue? Any input is appreciated. Thanks in advance. Vic. [log in to unmask]