Hi Ryan, Solder becomes liquid [not liquidous] when it exceeds its Liquidus temperature. If it is on a non-solderable surface, no metallurgical bond will form no matter how long it sits there in liquid form. On a solderable surface, it takes thermal energy, the amount will depend on the metals involved, to bring the base metal into solution with at least one constituent of the solder to form an intermetallic compound layer. The longer the time and the higher the temperature above Liquidus, the thicker the IMC layer. Also note, the IMC layer will also grow when the solder is not in liquid form by diffusion, but much slower. If the solder in liquid form is in contact with the base metal too short a time and/or the temperature of the solder/soldering surfaces is too low, the metallurgical bond [i.e. the formation of the IMC] may be inadequate for the requirements we impose on the solder. If you use vapor phase soldering, you can have the assembly at the vapor temperature for the time required for good soldering. In reflow and wave soldering, because longer dwell times equal ever higher temperatures, we have to worry on the one hand, about being in the peak reflow zone/solder wave too long and doing damage to the rest of the assembly, and on the other hand being there too shortand not get proper metallurgical bonds on all the solder joints in the assembly. A very fine balancing act, indeed! Werner Engelmaier Engelmaier Associates, L.C. Electronic Packaging, Interconnection and Reliability Consulting 7 Jasmine Run Ormond Beach, FL 32174 USA Phone: 904-437-8747, Fax: 904-437-8737 E-mail: [log in to unmask], Website: www.engelmaier.com --------------------------------------------------------------------------------- Technet Mail List provided as a free service by IPC using LISTSERV 1.8d To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt delivery of Technet send the following message: SET Technet NOMAIL Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail Archives Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ---------------------------------------------------------------------------------