Hi TechNet! Oh boy, another question for the metallurgists!! A eutectic transformation is when a liquid converts to two or more intimately mixed solids! Many metals have eutectic points on their phase diagrams. The reason to use a eutectic alloy of solder is that in manufacturing you can use the convenient liquid/solid switch as the on/off switch to facilitate handling, processing etc. The true eutectic for tin/lead is 61.9%tin/38.1%lead (183C)- everyone calls 63/37 or 60/40 eutectic but they are really near eutectic alloys. As for 62Sn, 36Pb, and 2Ag there is some literature published that shows the alloy is better in reliability than 63/37 - there is also data that says 62Sn, 36Pb, and 2Ag is no different than 63/37 so you will have to review the data to form an opinion. When chip capacitors didn't have barrier metals the 62Sn/36Pb/2Ag was used to help slow down leaching of the PdAg alloy off the chip capacitor end cap. Barrier metals are used by most chip capacitor fabricators today so leaching isn't an issue any more. Your "pasty" range of the 62Sn, 36Pb, and 2Ag alloy isn't very big so I don't think any preheater adjustments are necessary. Hope this is helpful. Dave Hillman Rockwell Collins [log in to unmask] ______________________________ Reply Separator _________________________________ Subject: Sub: Solder Paste Plastic or Eutectic Author: [log in to unmask] at ccmgw1 Date: 11/21/96 4:49 PM Question: If I have a solder paste that is 62Sn, 36Pb, and 2Ag, is this a Eutectic or Plastic range solder paste? 63Sn/37Pb is a Eutectic solder with a freeze point at 361 degrees "F". I am using a ESP paste at the above mix. The range of this solder is 354 - 372 degrees. If so it would seem to be a plastic solder. If this is true then I need to readjust my preheat temperatures at Wave Solder to compensate for the 354 degree low end of the solder paste to prevent reflow. Is this paste Eutectic or Plastic? Has anyone experienced this? Do I need a 62/36/2 paste like this? Why would a regular 63/37 paste work? *************************************************************************** * TechNet mail list is provided as a service by IPC using SmartList v3.05 * *************************************************************************** * To unsubscribe from this list at any time, send a message to: * * [log in to unmask] with <subject: unsubscribe> and no text. * *************************************************************************** *************************************************************************** * TechNet mail list is provided as a service by IPC using SmartList v3.05 * *************************************************************************** * To unsubscribe from this list at any time, send a message to: * * [log in to unmask] with <subject: unsubscribe> and no text. * ***************************************************************************