LEAD FREE SOLDERING - IMPACT ON ELECTROMECHANICAL RELAYS

摘要

On the basis of existing European regulations (ROHS Restrictions on the use of hazardous substances, WEEE Waste from electrical and electronic equipment) and upcoming similar Chinese regulations, many commonly used materials such as lead and cadmium will be forbidden in relay designs in the near future. For telecom and signal relays, lead-free soldering processes will have a major impact on designs and reliability in service, as the peak soldering temperature for SMD (Surface Mounted Devices) will increase by about 30℃ and will reach 250℃. In order to withstand the extremely high peak temperatures, the designs have to be modified and high-temperature-resistant materials have to be used. While soldering through-hole components (THT) does not require higher specifications for the components, the soldering process for lead-free surface mounted devices (SMT) depends much more on process parameters such as overheating of the components, ambient gas in the oven and solder paste used. SMD solder tests were performed with lead-free relays at 255℃. When proper materials are used and tried and tested manufacturing processes are applied, a similar reliability in service can be achieved for electromechanical relays after lead-free soldering. Special care must be taken with respect to moisture absorbed by the plastics. To ensure proper performance during the SMD soldering, dry packing of electromechanical relays must be considered.