Impact of lead-free soldering processes on the performance of signal relay contacts

Up to now, mainly tin-lead alloys have been used in electronics. The process temperatures usually applied have been in the range of 230°C. All currently discussed lead-free alternatives for professional electronics need process temperatures which are at least 30° higher. In addition, the process duration is significantly longer. The combination of higher process temperatures and longer duration together results in a significant thermal stress on the precision mechanics of the relay. In order to guarantee proper functioning of the relay after the solder process with maximum process temperatures of 255°C, the dimensional changes of the plastic parts must be less than a few micrometers in order to guarantee stable contact forces. The outgassing of the used insulating and sealing materials must be minimal in order not to pollute or contaminate the contacts. With the lead-free version of the IM relay, an identical performance and the same reliability during electrical and climatic endurance tests can be expected, even though relays were processed with typical lead-free soldering processes with temperatures up to 255°C.