The thermal mismatch could be a problem, but I think a far bigger problem is the thermal mass you need to heat up in order to reflow the solder. To reflow the part, you must feed it enough energy to bring it up to the melting point of the solder. A larger thermal mass needs more heat to reach the same temperature as a smaller part. Therefore, you will need to either: 1. Slow down your conveyor, possibly keeping the part in other stages of the reflow process too long; or 2. Apply a higher temperature in the reflow section of the oven. If you have other parts on the board, they will get damaged. The board itself may burn. If you really have to reflow the body of this part (and I wouldn't recommend it), try putting the one part on, reflow it at a high temperature, then place the componentsand reflow it at the regular temperature. Keep in mind this thermal mass may draw heat away from nearby components. Alan Hilton Emulation Technology ------- Forwarded Message Follows ------- Date: Thu, 27 Jun 1996 07:23:42 -0700 From: Eli Dallal <[log in to unmask]> Organization: Tadiran Telecommunications Ltd. To: [log in to unmask] Subject: TO220 reflow soldering Dear Techneters For years we have been reflow soldering TO 220 transistors to ceramic substrates to provide good thermal dissipation . now we want to use FR4 boards . Our intention was to bend the TO220 leads and insert them in pths and reflow solder the body of the transistor to the board on a suitable land and later wave solder the leads . But I was told that in pcbs it is customary to use screws and nuts or eylets instead of soldering .One explanation was that there is a big thermal mismatch but no one seemed to know for sure . What I would like to know if anyone has any experience in reflow soldering TO220 s to pcbs and if anyone knows why it should not be done. thanking you Eli Dallal process engineer Tadiran telecommunications =========================================================== Alan Hilton, P.Eng. Phone: (408) 982-0660 X213 R&D Engineer Fax: (408) 492-9170 Emulation Technology, Inc. eMail: [log in to unmask] 2344 Walsh Avenue Santa Clara, USA 95051-1301