Hi Wagner, Your observations are correct. The oven takes ~8 minutes to reach the shutoff temp, and probably 4-5 minutes to get back down to 50 deg C. It doesn't follow the approved reflow profile. I plotted the curve and it's a classic natural log ( Same as an triangular RC charge/discharge profile). for prototyping I think it's fine though. The heating profile is slow enough so that it sits at the preheat temperature long enough to evaporate the solder paste solvents. It doesn't have the rapid temp rise to the reflow point. My plans for the future???? are to use a 2nd micro to control the oven via the serial port to hold it at the preheat temp properly. As for the rapid temp to reflow, I am thinking of putting an IR ceramic heater in the top of the oven as a booster. Some other guys who have done a similar thing with an unmodified oven can be found at; http://www.seattlerobotics.org/encoder/200006/oven_art.htm Cheers, Peter Homann mailto:Peter.Homann@adacel.com Adacel Technologies Limited, 250 Bay St, BRIGHTON, 3186, AUSTRALIA http://www.adacel.com Telephone +61 (3) 8530 7777, Facsimile +61 (3) 9596 2960 Mobile 0421-601 665 -----Original Message----- From: pic microcontroller discussion list [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Wagner Lipnharski Sent: Monday, 18 November 2002 2:03 PM To: PICLIST@MITVMA.MIT.EDU Subject: Re: [EE]My PIC controlled SMT Reflow oven was RE:[EE] Hot air soldering = cheap was Re: [EE]: Printer to PCB? Peter Homann wrote: [snip] > Basically it worked like this. > > 1. The board was put in the oven > 2. The Start/Stop button was pressed. (The heater and fan turned on. > The LCD displays the current temperature) > 3. When the temp reaches the "Hi" set point (218 degs C) the Heater > turns off and the fan stays on to help cool the oven. (also the oven > door is opened at this point. > 4. When the temp reaches the "Lo" set point (50 Degs C), the fan > turns off. > 5. Take the board out and start again. > > The relays were to control the heating element and the fan. The rotary > encoder was for entering the Hi and Lo set points. > > If a "D" character is sent over the RS232 I/F, the oven will reply > with the current temp. > > Eventually I plan to replace the 84 with a 628 with twice the code > space. That way I can add to the RS232 command and have it controlled > by a computer or another PIC. The idea is to control the oven to get > a proper SMT temp profile. Peter, it is interesting. I always tought to test the single temperature slope as your solution does. The recommended paste soldering says a dual temperature slope, increase temperature to a certain point, hold there during some time, then increase temperature to a second setpoint, hold for a short time and turn off everything, just keep the fan active to cool it down. The first temperature slope is to heat everything, board, components, solder paste, and create a pre-solder environment, the second slope quickly melts the paste instantly, so, melting temperature is applied very briefly reducing the probable thermal damage to components. How long your oven takes to reach 2180C ? How long to cool down to 500C ? Probably you found a simpler way to do the same job. Did you ever logged the internal temperature in time (plotted a graph) ? Thank you. Wagner. -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads