Impact of Lead Free Soldering Processes on the Reliability of Electromechanical Switching Devices

摘要

Various effective and draft legislations and rules in Europe (WEEE - Waste Electrical and Electronic Equipment ROHS - Restrictions on the use of certain substances and ELV - End of life of vehicles) and Japan (Recycling Law for Home Electric Appliances) have either targeted restrictions or a full ban on the use of lead, to be enforced from 2001, 2003 and 2006 onwards. Up to now, mainly tin-lead alloys have been used in electronics. The process temperatures usually applied have been in the range of 230℃. All currently discussed lead-free alternatives for professional electronics need process temperatures which are at least 20° higher. In addition, the process duration is significantly longer. The combination of higher process temperatures and longer duration, results in a significant thermal stress on electromechanical devices. Especially the precision mechanics of electromechanical relays must withstand the solder process with maximum process temperatures of 255℃ without dimensional changes. During the transition from tin-lead to lead-free soldering processes all combinations of component surfaces and solder must be possible. The selection of pure Sn100 or SnCu0.7 as terminal surface allows mixed assemblies with tin-lead as well as lead-free solders. All tested combinations of terminal surface, PCB surface and solder showed good results. From these results it can be concluded that mixed assemblies are possible during the transition time without any negative impact on the reliability of the electronic devices.