Reflow of lead-free solder by microwave heating

Abstract

Recently, the use of solder containing lead in the interconnection between printed substrate and electric packages has been prohibited since lead may have a bad influence on humans and the environment. Today Sn-Ag-Cu alloys (SnAgCu) are used in general as a substitute of Sn-Pb alloys (SnPb). However, the melting point of SnAgCu is higher than that for SnPb which may induce damages in the substrate and packages. To solve this problem, the reflow of lead-free solder by microwave heating was studied. The microwave heating system worked at 2.45 GHz frequency on TE10 mode. The most suitable heating location in the waveguide and the most suitable microwave power were investigated by measuring the temperature of the substrate and the solder simultaneously. After the solder was heated up to the melting point of 493 K, solder-mounted was achieved. The intermetallic chemical compound between the solder and Cu was observed by SEM and it was also analysed by the cross-section of the solder using EDX.