Hi Eli - We have soldered TO 220s to organic substrates (FR4, BT, etc.) with very few problems. The reflow profile needs to be looked at for each assembly so that you heat up the all of the components uniformly but there is no "magic" in the process. I would not use any attachment hardware unless your use environment (e.g. lots of vibration) requires it - attachment hardware will increase your cost via assembly cycle time and material costs. Dave Hillman Rockwell Collins [log in to unmask] ______________________________ Reply Separator _________________________________ Subject: TO220 reflow soldering Author: [log in to unmask] at ccmgw1 Date: 6/26/96 11:37 PM 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