Real reflow lines do the first side with slightly higher melting temperarture solder then flip the board and use a slightly lower temp solder for the second side. The reflow ovens control the temperature VERY well (+/-.5C) and the bottom side (the side not getting the components ) is usually about 5C lower than what the top side is seeing. (top and bottom being the side getting the parts at this moment and the other side respectfully)
Mark -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Randall Nortman Sent: October 11, 2005 9:39 AM To: [email protected] Subject: Re: gEDA-user: Cheap 4 layer manufacturer? On Tue, Oct 11, 2005 at 10:12:02AM -0400, DJ Delorie wrote: > > > The oven a 1500-watt Oster, and was $60 at Target. It's got four > > heating elements (two top, two bottom) and, as I mentioned, a > > /me wonders if it's better to only heat the board from the bottom > (i.e. move all the heating elements to the bottom). For BGAs that > would mean that the heat didn't have to go through the heat-sensitive > BGA to get to the solder balls. Not a good idea if you want to be able to do boards with components on both sides. When doing the second side, there will be components on the bottom, and I think you would get them too hot by the time the top got hot enough to melt the solder there. I wonder -- do the real reflow ovens use bottom heat on the first side and then switch to top heat when doing the second side? Randall
