The Restriction of Hazardous Substances (RoHS) has been enforced a law to restrict the use of hazardous materials in electronic and electrical industries. Hence, it leads to the development of lead-free solder among the electronic industry. SnAg, SnCu, SnAgCu, and SnZnBi solders are found to be alternatives to replace SnPb solder alloys. However, they still have many problems, such as large undercooling and large intermetallic compounds are still present in the solder alloys. Later, researchers come up with the idea of adding alloying elements to lead-free solders to further enhance the properties of lead-free solders. This review paper is aimed to analyze and summaries the effects of germanium (Ge) addition to lead-free solders focusing on its microstructure and thermal properties. The Ge has an almost similar crystal structure as pure tin (Sn), so it is expected that the properties of the lead-free solder could be enhanced by adding an appropriate amount of Ge. Nevertheless, Ge has a unique characteristic as it could act as an antioxidant agent in the lead-free solders.
